Herb Fertilizer Guide · Updated August 2026
Best fertilizer for herbs: feed the herb you are actually growing.
The best fertilizer for herbs is not one product but one of two feeding programs, because rosemary and basil want opposite things from you. This guide sorts your herbs into those two groups, gives you the manufacturer application rates for pots, beds, and hydroponics, and shows you how to read the plant when something goes wrong.
See the quick answerThe short version
What Is the Best Fertilizer for Herbs?
The best fertilizer for herbs depends on which of two groups you are growing. Lean-feeding Mediterranean herbs, mostly woody sub-shrubs — rosemary, thyme, oregano, sage, marjoram, lavender, plus the herbaceous tarragon — do best on a lean, potassium-forward feed applied about once a month, such as Pepper & Herb Fertilizer 11-11-40 at 1.5 g per plant. Soft leafy herbs — basil, cilantro, parsley, mint, dill, chives — do best on a moderate-nitrogen, high-potassium leafy-green formula fed little and often, such as Lettuce Fertilizer 8-15-36 at 1–3 g per plant every 10 days. In containers and hydroponics, pair either one with a separate calcium source; in garden soil with regular compost, most herbs need very little beyond that[1][2].
Quick facts: fertilizing herbs
- Woody Mediterranean herbs (rosemary, thyme, oregano, sage, lavender): 11-11-40 at 1.5 g (about ¼ tsp) per plant in 1 gallon of water, monthly; skip feeding during winter dormancy. Over-feeding lowers flavor and aroma intensity and invites root and stem rot[1].
- Soft leafy herbs (basil, cilantro, parsley, mint, dill, chives): 8-15-36 at 1 g per plant while young and 3 g per plant in active growth, each in 1 gallon of water, every 10 days.
- Label notation: the three numbers are N–P₂O₅–K₂O. 11-11-40 runs a 3.6:1 K₂O:N ratio; 8-15-36 runs 4.5:1. Both are NPK-plus-micronutrient base formulas carrying EDTA-chelated iron, manganese, zinc, and copper. Neither contains calcium, so neither is a stand-alone complete nutrient solution — both are designed to be paired with a separate calcium source.
- pH targets: 6.0–7.0 in soil for most culinary herbs[2]; in hydroponic solution 5.8–6.3 on the 11-11-40 program and 5.6–6.2 on the 8-15-36 program, and never above about 6.5 if you rely on EDTA-chelated iron.
- Calcium and magnesium come from a separate product (Cal-Mag Plus) when you grow in containers, coco, or on RO or distilled water. Do not irrigate routinely with sodium-softened water — see water quality.
- Organic beds: a light per-plant nitrogen source for the leafy group only, plus kelp meal for trace minerals. Mediterranean herbs in amended soil usually need nothing.
- Edible-crop checkpoint: ask for the dated heavy-metal report for the product and lot you buy — worth doing for anything applied to a crop you eat.
Rates above are Greenway product guidance from the live product pages (retrieved August 24, 2026); if a product page and this article disagree, the product page governs. The rest of this guide is the agronomy behind those numbers and how to adjust them for your water, light, and soil.
Two kinds of herbs
Best Fertilizer for Basil, Mint, Parsley, and Other Common Herbs
Sort the herb first, then pick the program. Nearly every herb-feeding mistake comes from treating rosemary like basil. The two groups are a working heuristic for feeding, not a botanical division — individual herbs still vary, so treat the rates as starting points and adjust to what the plant does.
Lean-feeding Mediterranean herbs — rosemary, thyme, oregano, marjoram, sage, lavender, winter savory, and the herbaceous tarragon — are mostly shrubs or sub-shrubs from sunny, dry, stony ground. Extension guidance is consistent: they grow best on light, sharply drained soil that is not especially fertile, and highly fertile conditions produce excess foliage that is poor in flavor[1][2]. They are harvested a few stems at a time, so they never need to rebuild a whole canopy. A lean, potassium-forward feed once a month during active growth is enough; in a compost-amended bed, one light application at the start of the season is often all they get.
Soft leafy herbs — basil, cilantro, parsley, mint, dill, chives, chervil — are the opposite case. They prefer richer, evenly moist soil[2], and you harvest them by cutting the whole plant back every week or two, which removes most of the nitrogen just invested in leaves. Feed them the way leafy greens are fed: moderate nitrogen, high potassium, small doses, short intervals. Too much nitrogen still costs flavor and shelf life — it just takes more of it than with thyme.
| Herb | Group | Base product | Container rate (per plant, in 1 gal water) | How often | Notes |
|---|---|---|---|---|---|
| Basil | Soft leafy | Lettuce Fertilizer 8-15-36 | 1 g young; 3 g in active growth | Every 10 days | Rich, well-drained soil; harvest before flowering to keep flavor[2]. Sensitive to low magnesium and iron in hydroponics[5]. |
| Mint | Soft leafy | Lettuce Fertilizer 8-15-36 | 1 g young; 3 g in active growth | Every 10 days | Prefers rich, moist soil and part shade; confine to a container or it spreads[2]. |
| Parsley | Soft leafy | Lettuce Fertilizer 8-15-36 | 1 g young; 3 g in active growth | Every 10 days | Biennial with a taproot; rich, moist soil, tolerates light shade[2]. |
| Cilantro | Soft leafy | Lettuce Fertilizer 8-15-36 | 1 g young; up to 3 g in active growth | Every 10 days | Bolts in heat regardless of feeding — cool-season timing matters more than fertilizer[2]. Stay at the low end. |
| Dill, chives, chervil | Soft leafy | Lettuce Fertilizer 8-15-36 | 1 g young; 3 g in active growth | Every 10 days | Cut back regularly to keep fresh growth coming. Chervil is one of the few herbs that wants moderate fertility even in soil[1]. |
| Thyme | Mediterranean | Pepper & Herb 11-11-40 | 1.5 g | Monthly; none in winter dormancy | Full sun, very well-drained soil that stays dry[2]. Excess nitrogen gives soft, weak growth. |
| Rosemary | Mediterranean | Pepper & Herb 11-11-40 | 1.5 g | Monthly; none in winter dormancy | Dry, sunny, well-drained sites[2]. Over-fertilizing causes more problems than under-fertilizing. |
| Oregano, marjoram, sage, lavender, tarragon | Mediterranean | Pepper & Herb 11-11-40 | 1.5 g | Monthly; none in winter dormancy | Full sun and excellent drainage[2]; flavor and aroma intensity are typically higher in plants grown lean. Wet feet, not hunger, kills most sage; lavender needs the sharpest drainage of the group. |
If you own only one of the two products, you can still feed both groups: soft herbs on 11-11-40 take the woody-herb rate on the lower side plus a light nitrogen companion during heavy cutting (Greenway product guidance); woody herbs on 8-15-36 take the 1 g young-plant rate no more than monthly. The plant will tell you if you got it wrong — see diagnosing herb fertilizer problems.
Why plant family is a rough guide, not the rule
Basil and rosemary share a botanical family (Lamiaceae), which is why family alone does not predict feeding — growth habit and harvest pattern do. Umbellifers (parsley, cilantro, dill) and alliums (chives) behave like the soft group; sub-shrubs behave like the woody group whatever their family. Peppers are not herbs, but they are the other crop 11-11-40 was built for and take roughly twice the woody-herb rate; that program lives in Best Fertilizer for Peppers.
Reading the label
NPK Ratios for Herb Fertilizers: What the Numbers Mean
The three numbers on a fertilizer label are the guaranteed analysis of nitrogen (N), available phosphate (P₂O₅), and soluble potash (K₂O), in that order. Nitrogen is expressed as the element; phosphorus and potassium are expressed as their oxide equivalents, which is the standard across the U.S. fertilizer industry. So 8-15-36 means 8% N, 15% P₂O₅, and 36% K₂O by weight — not 36% elemental potassium.
Nitrogen drives leaf and stem growth. Herbs harvested for foliage rely on it to rebuild the canopy after each cutting. But nitrogen is also the nutrient herb growers most often overdo: very fertile conditions produce lush, soft leaves that lack flavor and are more prone to root and stem rot[1][2]. That is why a purpose-built leafy formula like 8-15-36 keeps nitrogen at a moderate 8%, and why the woody group gets nitrogen only in small monthly doses.
Available phosphate (P₂O₅) supports root establishment, energy transfer, and early growth. Herbs are not heavy phosphorus users, and in garden soil phosphorus should be applied to soil-test need rather than by habit — excess phosphate can interfere with zinc and iron uptake. In soilless media and hydroponics, where there is no soil reserve, the 11–15% P₂O₅ in these base formulas covers the requirement.
Soluble potash (K₂O) regulates water relations inside the plant: it controls the guard cells that open and close stomata, is required for the activity of dozens of enzyme systems, and drives the transport of sugars and secondary compounds. In aromatic herbs, adequate potassium supports overall plant function and is one of several inputs behind flavor and aroma intensity, alongside genetics, light, harvest timing, and temperature. It is not a lever you can push without limit: excess potassium antagonizes calcium and magnesium uptake, and basil is sensitive to magnesium shortfall[5].
Why sun and lean soil matter more than fertilizer for aroma
The aromatic compounds that give basil, mint, and thyme their character are produced in tiny glandular structures on the leaf surface called trichomes. Extension guidance is that these compounds are produced in the greatest quantity when plants receive plenty of sun, and that over-fertilizing lowers their concentration[1][2]. Good nutrition keeps the plant healthy enough to make them; it does not substitute for light, and more fertilizer does not mean more flavor.
That is why the two Greenway herb programs look the way they do. 11-11-40 (3.6:1 K₂O:N) supplies potassium-dominant nutrition with just enough nitrogen for a plant that is never cut hard. 8-15-36 (4.5:1 K₂O:N) supplies moderate nitrogen for a plant that is cut hard every week, with high potash to support water regulation and enzyme activity — though texture and post-harvest quality depend on the whole nutrient and environmental program, not potassium alone. Both carry EDTA-chelated iron, manganese, zinc, and copper plus boron and molybdenum, and both deliberately leave calcium out (see water quality).
Related reading: What’s the Function of Potassium in Plants? · What’s the Function of Nitrogen in Plants?
The trace package
Why Chelated Micronutrients Matter for Herbs
Iron, manganese, zinc, copper, boron, and molybdenum are needed in parts per million rather than percentages, but they are as essential as N, P₂O₅, and K₂O. The problem with the first four is chemistry: as metal ions in solution they react with oxygen and hydroxide, and above about pH 6.5 they precipitate into forms roots cannot absorb[3]. Iron is the textbook case — abundant in most soils and still one of the most common deficiencies, because it is present but unavailable.
Chelation solves availability rather than supply. A chelating ligand such as EDTA wraps the metal ion in a ring that shields it from those reactions, keeping it dissolved and plant-available until a root exchanges it out[3]. Stability falls off gradually as pH rises rather than failing at a single point, and each ligand holds on over a different range: EDTA holds iron well through about pH 6.5 and retains very little by 7.5; DTPA is only partly effective at 7.5; EDDHA holds into strongly alkaline conditions[3]. In soilless media and hydroponics, where pH drifts between reservoir changes, chelated form is the difference between a micronutrient on the label and one that reaches the plant.
Boron and molybdenum do not form the same insoluble compounds, so they are supplied as boric acid and sodium molybdate without chelation. When you compare herb fertilizers, look for the chelated forms named on the label (Fe-EDTA, Mn-EDTA, Zn-EDTA, Cu-EDTA), and keep your solution pH under about 6.5, where EDTA still holds most of its iron. If your soil or water runs persistently above pH 7, a DTPA iron source is the steadier choice for correcting chlorosis.
Related reading: Sulfate vs. Chelated Fertilizers: What’s the Difference? · browse the micronutrients & chelated fertilizers collection.
The overlooked variable
Water Quality and Herb Fertilization
If herbs struggle despite a sensible feeding program, test the water before you raise the rate.
Water chemistry decides how a fertilizer performs, and it matters most in exactly the situations where herbs are usually grown: small pots, windowsills, and recirculating reservoirs. Two measurements tell most of the story. pH is the water’s acidity. Alkalinity is its buffering capacity — the load of bicarbonate and carbonate it carries — and it is alkalinity, not pH, that has the larger effect on root-zone chemistry[4]. Water with high pH but low alkalinity is usually harmless. Water with high pH and high alkalinity acts like a dilute limestone solution: it pushes root-zone pH up over time, most severely in small containers that have little buffering, and it produces trace-element deficiencies and calcium–magnesium imbalances[4].
Three water problems that look like fertilizer problems
- Hard, high-alkalinity water. Root-zone pH creeps upward, iron and manganese lock out, and the new leaves yellow between the veins even though both metals are in the fertilizer[3][4]. Adding more iron treats the symptom; the fix is pH correction or blending in RO or rainwater. Municipal water commonly runs pH 7.0–8.5 because of the carbonates added to protect pipes[5].
- RO or distilled water. These carry almost no calcium or magnesium, and since neither base formula contains calcium, all of it must come from a separate product. Cal-Mag Plus 2-0-0 is built for this: roughly 5 ml of stock per gallon on medium tap water and the full 10 ml per gallon on RO, always into the water first.
- Sodium-softened water is a different problem, and Cal-Mag does not fix it. A conventional ion-exchange softener removes calcium and magnesium by replacing them with sodium, and adding a calcium supplement does not remove that sodium. Extension guidance is not to use sodium-softened water for irrigation; take water from an unsoftened outdoor tap or bypass line, or use rainwater or remineralized RO instead. If your softener runs on potassium chloride rather than sodium, test the water before you build a feed program around it.
- High sodium or chloride. Osmotic stress from salty water shows as leaf-tip burn and marginal scorch that is indistinguishable from fertilizer burn. Only a water test separates the two.
Moderate alkalinity, about 30–60 ppm as calcium carbonate, is actually useful — it supplies some of the calcium and magnesium soluble fertilizers leave out[4]. Above roughly 30 ppm calcium in the source water, start Cal-Mag Plus low and add only what a water report shows you need.
Water checklist before you raise a fertilizer rate
- Measure pH. Root zone or solution: correct to 6.0–7.0 for herbs in soil, and 5.6–6.3 for hydroponics depending on the program (see the rate tables).
- Get an alkalinity number. A pH test alone does not tell you alkalinity[4]. Your utility’s water report or a $15–30 irrigation water test will.
- Hard water? Blend with RO or rainwater, or acidify carefully; keep the EDTA-chelated iron in your fertilizer working by holding solution pH under 6.5.
- RO or distilled water? Add Cal-Mag Plus first, separately, every time. Sodium-softened water? Do not use it — switch to an unsoftened tap, rainwater, or remineralized RO.
- Tip burn that persists after pH and rate are correct? Test for sodium and chloride.
Before you buy
Choosing the Best Herb Fertilizer for Your Garden
The two-program approach works well for most herb growers, but your water, your soil, and what else is growing in the pot change the answer. Find your situation below.
| Your situation | Best approach |
|---|---|
| Growing woody Mediterranean herbs (rosemary, thyme, oregano, sage, lavender) in pots, beds, or hydroponics | Pepper & Herb 11-11-40 at the woody-herb rate: 1.5 g per plant monthly in containers, 1 g per plant established in hydroponics. Let them run lean; in amended garden soil, one light feeding at the start of the season is often enough. |
| Growing soft leafy herbs (basil, cilantro, parsley, mint, dill, chives) | Lettuce Fertilizer 8-15-36 at the seedling and active-growth rates, every 10 days in containers; in hydroponics, hold EC toward the low end of the lettuce bands. |
| A mixed herb pot or bed with both groups | Feed to the group that dominates, or split the planting. If you own only 11-11-40, use the woody-herb rate on the soft herbs and add a light nitrogen companion during heavy cutting; if you own only 8-15-36, give the woody herbs the 1 g rate no more than monthly. |
| Herbs growing alongside peppers | One bag of 11-11-40, two rates — 3 g per pepper every 2 weeks, 1.5 g per woody herb monthly. Move soft herbs to their own pot. |
| Established garden soil with regular compost | Test first, and work to an annual nitrogen budget. Mediterranean herbs usually need nothing beyond compost. Soft herbs benefit from a light per-plant nitrogen side-dress of Blood Meal 13-0-0 and a trace-mineral base from Kelp Meal 2-0-4 (see organic options below). |
| Strictly organic program | 11-11-40 and 8-15-36 are synthetic blends and are not OMRI Listed®. Use the organic program: kelp meal (repackaged from OMRI Listed® material) plus, for the leafy group only, blood meal (the 40 lb bag is repackaged from OMRI Listed® material). |
| Hard water, or persistent yellowing that feeding does not fix | Test water alkalinity and root-zone pH before adding anything. Bicarbonate-driven pH rise is the most common cause of “deficiency” in fed herbs[4]. |
| RO or distilled water, or coco coir | Add Cal-Mag Plus first, separately, at every feeding: about 5 ml stock per gallon on medium tap water, 10 ml per gallon on RO. Coco binds calcium and needs it regardless of water hardness. Sodium-softened water is not suitable for irrigation at all — Cal-Mag does not remove the sodium. |
| Interveinal chlorosis on new growth | Check pH first (soil at or below 7.0; solution 5.6–6.3 by program). If pH is right, supplement with chelated iron; if iron does not resolve it within two weeks, manganese is the next thing to test. |
| Soil test shows already-high phosphorus or potassium | Skip the base formula. Supply only what is short — usually a little nitrogen for the leafy group and nothing for the woody group. |
| Seedlings, transplants, or herbs on an indoor windowsill | Use the seedling rates for the first 2–3 weeks. Indoors, halve the container rate and stretch the interval; slow-growing plants take up far less than the label assumes[5] — see indoor herbs. |
Soil pH and herb nutrition
Most culinary herbs perform well at a soil pH of 6.0–7.0[2]; the woody Mediterranean group tolerates the upper end of that range and slightly beyond. Outside it, even a well-formulated fertilizer underperforms because of nutrient lockout — iron and manganese above about 6.5–7.0, phosphorus at both extremes. Check pH before adding fertilizer whenever growth is poor despite regular feeding. Clemson bases herb fertilizer and lime recommendations on a soil test rather than a standard rate[2]; most university labs run a pH, organic matter, and macronutrient panel for $15–30. For the mechanics, see Why Soil pH Plays a Bigger Role in Your Garden Than You Might Think.
Application rates
How to Fertilize Herbs
Every rate below is Greenway product guidance as published on the live product pages, retrieved August 24, 2026. The product page and registered label govern if anything here ever disagrees.
Lean-feeding Mediterranean herbs in containers — Pepper & Herb 11-11-40
Concentration: 1.5 g (about ¼ tsp) of 11-11-40 per gallon of water — one plant’s allotment.
Application volume: apply over already-moist media until the root zone is evenly wet and a little drains from the bottom, then stop. A 6-inch pot takes far less than a gallon; a large patio pot or several small pots will use the rest. Do not force a full gallon through one small container.
Dose received: up to 1.5 g per plant per feeding — less if the plant is small and you apply less than its full gallon.
How often: monthly during active growth; none during winter dormancy.
Worked example: six rosemary plants = 6 × 1.5 g = 9 g mixed into 6 gallons, divided among the six pots, once a month.
At potting: ¼ tsp per gallon of potting mix, mixed in once.
Between feedings: about 5 ml of Cal-Mag Plus stock per plant on RO or distilled water; flush the pot with plain water once a month.
Soft leafy herbs in containers — Lettuce Fertilizer 8-15-36
Concentration: 1 g (a scant ¼ tsp) of 8-15-36 per gallon of water while the plant is young; 3 g (a generous ½ tsp) per gallon in active growth — one plant’s allotment at each stage.
Application volume: apply over moist media until the root zone is evenly wet with slight drainage. Small pots take a fraction of a gallon; use the remainder on the rest of the planting.
Dose received: up to 1 g per young plant and 3 g per established plant per feeding, scaled to how much of the gallon that plant actually gets.
How often: every 10 days.
Worked example: four basil plants in active growth = 4 × 3 g = 12 g mixed into 4 gallons, divided among the four pots, every 10 days.
Herb note: stay on the 1 g and 3 g steps. The 5 g rate on the lettuce label is for filling a mature head, not for cut-and-come-again herbs, and Greenway product guidance for leafy herbs is to run slightly below lettuce.
At potting: ½ tsp per gallon of potting mix. Between feedings: about 5 ml of Cal-Mag Plus stock per plant; flush monthly.
Hydroponic herbs — per plant, either program
Neither 11-11-40 nor 8-15-36 is a stand-alone hydroponic solution — both are NPK-plus-micronutrient base formulas with no calcium. A workable herb reservoir is the base formula plus Cal-Mag Plus, plus calcium nitrate on RO or low-alkalinity water. The table below is Greenway’s published per-plant program with all three parts: multiply every column by your plant count, mix into the reservoir, then bring the volume up until you hit the target EC.
EC is not a completeness check
EC measures total dissolved ions. It tells you how concentrated a solution is, not whether calcium, magnesium, nitrogen, and the micronutrients are in balance — two solutions at the same EC can be nutritionally very different. Use the elemental ppm column as the real target and treat EC as a working check once the recipe is right. If you are running a commercial or high-value herb crop, have a nutrient program validated against a solution analysis rather than relying on a general-purpose table.
Cal-Mag Plus amounts are ml of prepared stock (2.5 lb of powder dissolved per gallon of water). Order of addition: water first, then Cal-Mag Plus, then calcium nitrate if used, then the base fertilizer last — never combine the calcium products with the base formula in concentrated form. Then set pH and verify EC.
| Herb group / product | Stage | Base fertilizer per plant | Cal-Mag Plus stock per plant | Calcium nitrate per plant (RO / low-alkalinity water) | Water per plant | Approximate elemental ppm at this rate | Final EC (mS/cm) | pH |
|---|---|---|---|---|---|---|---|---|
| Mediterranean herbs — 11-11-40 | Seedling / transplant | 0.4 g | 2 ml | 0.3–0.5 g | 0.6–0.8 gal | N 30–40, P 8–10, K 40–50, Ca 35–50, Mg 5–7 | 0.8–1.0 | 5.8–6.3 |
| Mediterranean herbs — 11-11-40 | Established, mature | 1 g (about ⅕ tsp) | 6 ml | 0.6–1.0 g | 0.8–1.0 gal | N 55–70, P 13–16, K 88–110, Ca 55–75, Mg 6–7 | 1.2–1.5 | 5.8–6.3 |
| Soft herbs — 8-15-36 | Seedling / transplant | 0.8 g | 3 ml | 0.4–0.6 g | 0.8–0.9 gal | N 35–45, P 16–18, K 74–83, Ca 35–45, Mg 3–4 | 0.8–1.0 | 5.8–6.2 |
| Soft herbs — 8-15-36 | Cut-and-come-again growth | 1.5 g | 6 ml | 0.6–1.0 g | 0.8–0.9 gal | N 85–100, P 29–33, K 133–150, Ca 60–80, Mg 6–7 | 1.2–1.6 — hold to the low end for herbs | 5.6–6.0 |
Worked example: eight basil plants in cut-and-come-again growth on RO water = 8 × 1.5 g = 12 g of 8-15-36, 8 × 6 ml = 48 ml of Cal-Mag Plus stock, 8 × 0.8 g = 6.4 g of calcium nitrate, and about 7 gallons of water, adjusted until the reservoir reads about 1.2–1.4 EC. Replace the solution every 7–14 days — commercial basil guidance calls for a full replacement every 1–2 weeks[5] — and top up with plain water, not more fertilizer, in between. On the 500 scale, ppm = EC × 500; on the 700 scale, ppm = EC × 700. Companion calcium products are in the hydroponic nutrients collection. Skipping the calcium components leaves this program well short of the calcium and magnesium levels used in published hydroponic basil work, so treat them as required parts of the recipe rather than optional extras.
In-ground and raised beds — fed by area, not by plant
Beds are fed per 100 square feet, so plant count does not change the amount; split it evenly and water it in. For 1,000 sq ft, multiply by ten.
- Mediterranean herbs (11-11-40): 0.25 lb (about 113 g) per 100 sq ft worked into the top few inches once before planting — light feeding only, then let them run lean. Drip fertigation: 0.125–0.25 lb per 100 gallons of irrigation water, monthly.
- Soft herbs (8-15-36): 1 lb per 100 sq ft plus 2 inches of compost before planting; then 0.25 lb (about 113 g) per 100 sq ft side-dressed every 2 weeks during cut-and-come-again harvest, sprinkled around the plants without touching stems. Drip fertigation: 0.5 lb per 100 gallons, weekly in active growth.
- Soil test first. These are general rates for medium-testing soils; a current soil test and your local extension office set the final number.
Foliar feeding on herbs: avoid it on any herb you will eat fresh. For transplant establishment only, Greenway product guidance for 11-11-40 is 1–2 g per gallon during transplant week, stopping at least 14 days before harvest. Each product page carries a calculator that sizes these rates to your plant count or bed area, and the free fertilizer calculator covers the rest of the catalog.
Three common application mistakes
- Feeding dry plants. Water with plain water first. Concentrated solution on a dry root zone burns root tips.
- Never flushing. Soluble fertilizer salts and hard-water minerals stay behind when water evaporates, compete with roots for moisture, and can shift media pH and block nutrient uptake[6]. Flush containers from the top with at least three times the pot volume of plain water[6], and empty the saucer so the salts do not soak back in. University of Maryland Extension suggests leaching indoor plants every 4–6 months[6]; Greenway product guidance for herbs on a regular liquid-feed program is monthly, because you are adding salts far more often than a houseplant owner does.
- Feeding a stressed plant. A wilted, root-bound, or diseased herb cannot use fertilizer. Fix the cause first; fertilizer applied to a stressed plant rarely helps and often makes it worse.
Windowsills and grow lights
Best Fertilizer for Indoor Herbs and Windowsill Gardens
Indoor herbs are the same plants on a different budget: light sets the growth rate, and growth rate sets nutrient demand. In a University of Florida trial, hydroponic basil grown indoors under modest light produced roughly a quarter of the fresh weight of the same basil in a greenhouse and took up far fewer nutrients — so much less that a reservoir run on the greenhouse schedule without replacement climbed above 5 mS/cm by week six. The authors concluded that indoor programs need reduced fertilizer input, not the commercial rate[5].
Salt buildup is the indoor failure mode. A slow-growing plant in a small pot leaves most of what you apply behind. The white crust on the soil surface or pot rim is fertilizer and hard-water salts; they compete with roots for moisture, scorch leaf tips and margins, and can push media pH out of range[6]. Those symptoms are frequently misread as deficiency and treated with more fertilizer, which makes them worse.
Fungus gnats are a fertilizer-adjacent problem. Constantly moist indoor mix attracts them, and their larvae feed on fine roots — a chewed root system shows deficiency symptoms on a perfectly good feeding program. If symptoms appear suddenly in a stable indoor pot, let the surface dry between waterings and check root health before touching the fertilizer.
Indoor herb feeding recommendations
- Rate: half the container rate for herbs in ordinary window light — about 0.75 g of 11-11-40 per woody herb, or 0.5–1.5 g of 8-15-36 per soft herb, each in 1 gallon of water. This is research-derived guidance for low light, not a label rate[5].
- Interval: woody herbs every 6–8 weeks; soft herbs every 2–3 weeks, and only while they are being cut and regrowing.
- Under grow lights: move back toward the full container rate and interval as light increases; growth rate and demand scale together[5].
- Flush: from the top, with at least three times the pot volume of plain water[6]; let it drain completely and empty the saucer. Monthly on a regular feeding program (Greenway product guidance); every 4–6 months is UMD’s interval for lightly fed indoor plants[6].
- Water temperature: room temperature. Cold tap water on a warm indoor root zone slows uptake.
- Countertop hydroponic units: use the seedling rates from the hydroponic table and replace, rather than top up, the solution on schedule.
Read the plant
Diagnosing Common Herb Fertilizer Problems
Most herb nutrient problems show visible symptoms well before they cost you a harvest, and most are not shortages at all — they are pH, water, or root problems that look like shortages. Confirm before you treat.
| Symptom | Possible causes | How to confirm | What to do |
|---|---|---|---|
| Yellowing that starts on the older, lower leaves and moves up | Nitrogen running short (common in heavily cut soft herbs); or overwatering and root damage | Check the roots and the media. White, firm roots in mix that is not waterlogged point to nitrogen. | Soft herbs: feed at the active-growth rate and recheck in 10–14 days. Woody herbs: this is rarely hunger — fix drainage first. |
| Yellow new leaves with green veins (interveinal chlorosis on young growth) | Iron or manganese unavailable — usually high root-zone pH or high-alkalinity water, not a shortage in the fertilizer[3][4] | Measure solution or root-zone pH; get the water’s alkalinity from your utility report or a test. | Correct pH first. If pH is already right, apply Chelated Iron EDTA (1 tsp per gallon foliar, or 2–3 ppm Fe in a reservoir). If two weeks of iron changes nothing, test and treat with Chelated Manganese EDTA. |
| Yellowing between the veins on older leaves, especially basil | Magnesium shortfall, often induced by high potassium or calcium rather than true absence[5] | Older leaves first, veins stay green. In hydroponics, compare your Cal-Mag dose against the tables above. | Add or increase Cal-Mag Plus (it supplies magnesium as well as calcium); do not stack extra potassium on top of a high-potash base. |
| Brown, crisp leaf tips or scorched margins | Soluble-salt buildup from feeding or hard water; low humidity; sodium or chloride in the water[6] | Look for white crust on the media or pot rim; test the water if it recurs after flushing. | Flush with three times the pot volume of plain water[6], cut the rate by a quarter to a half, and empty the saucer after watering. |
| Lush, soft growth that wilts easily; weak aroma | Excess nitrogen — typically a woody herb being fed like basil, or low light[1][2] | Compare what you applied against the woody-herb rate; check hours of direct sun. | Skip one or two feedings, move woody herbs to the monthly 1.5 g rate, improve light, harvest more often. |
| Stunted growth with good leaf color | Root-bound container, overwatering, cold root zone, or pH out of range | Slide the plant out and look at the root ball; check pH. | Repot, fix drainage, or correct pH. A fertilizer change alone will not resolve this. |
| Wilting in a hydroponic system despite plenty of solution; roots brown, slimy, and sour-smelling | Root rot — Pythium spp. is the primary hydroponic root-rot pathogen, though other water molds can be involved, usually alongside warm, oxygen-poor solution | Healthy roots are white and firm; brown, slimy roots indicate rot but not which organism. A lab or extension diagnostic confirms it. | Not a nutrition problem. Aerate, cool the solution, sanitize, and follow the recovery steps in Root Rot in Hydroponics. |
| Purple or reddish tint on the undersides of young leaves | Often phosphorus uptake limited by a cold root zone rather than a shortage in the fertilizer — but purple pigment also comes from cultivar genetics, high light, and other stresses | Check root-zone temperature and whether the cultivar is naturally purple-tinged; cold-driven symptoms typically fade as it warms. | Warm the root zone. Do not add phosphate on a just-in-case basis; excess P₂O₅ interferes with zinc and iron. |
Document before you treat
Photograph the symptom, note whether it started on old or new leaves, and record pH and EC if you have them. Deficiency symptoms in herbs mimic disease and salt injury, and treating one as the other makes things worse. Greenway’s deficiency diagnosis tool walks the pattern; see also 8 Reasons Why Plant Leaves Turn Yellow and Fertilizer Toxicity vs. Nutrient Deficiency. Many county Cooperative Extension offices offer low-cost plant diagnosis.
Meals and biostimulants
Organic Fertilizer for Herbs
The two crop formulas above are synthetic blends and are not OMRI Listed®. If you grow to organic standards, herbs are among the easiest crops to feed, because most of them want so little. The program splits the same way the rest of this guide does.
Lean-feeding Mediterranean herbs: compost, drainage, and a trace-mineral base
In a bed amended with moderate compost, rosemary, thyme, sage, and oregano usually need no added nitrogen at all — extension guidance is that highly fertile soil works against them[1][2]. If you want a biostimulant and broad trace-mineral base, Kelp Meal 2-0-4 (repackaged from OMRI Listed® Ascophyllum nodosum) fits: 1 tsp mixed into the backfill of each transplant hole, or 0.5–1 lb per 100 sq ft worked into the top 3 inches of a new bed; in containers, 0.5–1 tbsp per gallon of potting mix at potting time. At 2% nitrogen and slow microbial release it will not push soft growth. Skip nitrogen meals on this group entirely.
Soft leafy herbs: a light nitrogen side-dress plus kelp
Basil, parsley, cilantro, and mint that are cut every week do need nitrogen returned to them. Blood Meal 13-0-0 is the fastest-releasing organic source, with a typical response in 1–3 weeks in warm, moist soil; the 40 lb bag is repackaged from OMRI Listed® material. Greenway product guidance: in containers, 1–2 tsp per gallon of potting mix at planting, then 1 tsp per 6-inch pot side-dressed monthly during active growth; in beds, 1–2 tsp per plant monthly. Work it into the top 2–3 inches, keep it off the stems and the harvestable leaves, and water it in. Feed per plant rather than broadcasting a bed rate. Blood meal is 13% nitrogen, so the general bed-preparation rates on the product page put well over 1 lb of actual nitrogen per 1,000 sq ft into a single application — more than a low-demand crop like herbs needs and above the usual single-application guideline. Work from a soil test and an annual nitrogen budget for the bed, and count every source, including compost. Pair it with kelp meal at the rates above for trace minerals. Because release depends on soil microbes, expect little from either meal in soil below about 50–55°F, and do not expect either to work in a hydroponic reservoir — that is where the soluble formulas belong.
Handling blood meal
- It attracts animals. The smell draws dogs, cats, raccoons, and rodents, which will dig in a freshly amended bed or pot. Always work it into the soil rather than leaving it on the surface, and water it in.
- Wear a dust mask. It is a fine, dusty powder; avoid breathing it and mix on a still day.
- Over-application burns. At 13% nitrogen it is concentrated for an organic input — too much causes leaf burn and forces soft, floppy growth on exactly the herbs you want compact.
- It is a nitrogen-only input. It supplies no phosphorus, potassium, or micronutrients; pair it with compost and kelp meal rather than using it alone.
Organic program at a glance
- Mediterranean herbs: compost + kelp meal at planting; nothing else.
- Soft herbs: compost + kelp meal at planting; per-plant blood meal side-dress monthly while cutting, to a soil test.
- Hydroponics: organic meals are not a fit; use the soluble programs.
- More in the organic fertilizers collection and Best Organic Fertilizer for Vegetables.
Greenway Biotech herb program
Two formulas, one calcium companion, one chlorosis fix
Every product below is CDFA registered, 100% water-soluble, and blended in Madera, California. Ask for the dated heavy-metal report for your product and lot — a relevant checkpoint for anything applied to a crop you eat. Full lineup: peppers & herbs collection.
Pepper & Herb Fertilizer 11-11-40
Potassium-forward base formula with chelated micros. Monthly at 1.5 g per plant for rosemary, thyme, oregano, sage, lavender — and the peppers next to them.
Soft leafy herbsLettuce Fertilizer 8-15-36
Moderate nitrogen, high potash, chelated micros. Every 10 days at 1–3 g per plant for basil, cilantro, parsley, mint, dill, chives.
Calcium & magnesiumCal-Mag Plus 2-0-0
The separate calcium and magnesium source both base formulas are designed around. Goes into the water first; required on RO or distilled water and in coco.
Chlorosis fixChelated Iron EDTA 13%
For yellow new growth with green veins once pH is confirmed at or below 7.0. Foliar at 1 tsp per gallon, or 2–3 ppm Fe in a reservoir.
Mixing and compatibility
Dissolve each product separately in its own bucket before it goes into the reservoir or watering can, and never combine a calcium concentrate (Cal-Mag Plus, calcium nitrate) with a concentrated phosphate- or sulfate-containing fertilizer — insoluble calcium phosphate and calcium sulfate precipitate out and neither nutrient reaches the plant. In the diluted working solution, water goes in first, calcium second, the base fertilizer last; then adjust pH and verify EC. Jar-test any combination you have not run before. Questions about a specific setup: questions@greenwaybiotech.com · (562) 351-5168 · Mon–Fri 7AM–5PM PST.
Summary
Key takeaways
- The best fertilizer for herbs is a program, not a product: woody Mediterranean herbs get a lean, potassium-forward monthly feed; soft leafy herbs get moderate nitrogen and high potassium little and often.
- Woody herbs (rosemary, thyme, oregano, sage, lavender): Pepper & Herb 11-11-40 at 1.5 g per plant in 1 gallon of water, monthly, none in winter dormancy. Over-feeding this group lowers flavor and aroma intensity and encourages rot[1][2].
- Soft herbs (basil, cilantro, parsley, mint, dill, chives): Lettuce Fertilizer 8-15-36 at 1 g per plant while young and 3 g in active growth, in 1 gallon of water, every 10 days.
- Labels read N–P₂O₅–K₂O. Neither formula contains calcium, so neither is a stand-alone complete solution; add Cal-Mag Plus separately, first, on RO or distilled water and in coco. Do not irrigate with sodium-softened water.
- Water alkalinity, not pH alone, drives most “deficiencies” in fed herbs[4]. Keep soil pH at 6.0–7.0 and solution pH at 5.8–6.3 so EDTA-chelated iron stays available[3].
- Indoor herbs grow slower and take up less: halve the rate, stretch the interval, and flush pots with three times their volume of plain water[6] — monthly if you feed monthly[5]. In compost-amended garden soil, woody herbs usually need nothing and soft herbs take a light blood meal side-dress plus kelp meal — soil-test first.
Questions we get
Frequently asked questions
What is the best fertilizer for herbs in pots?
It depends on the herb. Woody Mediterranean herbs in pots do well on Pepper & Herb 11-11-40 at 1.5 g per plant in 1 gallon of water once a month. Soft leafy herbs do well on Lettuce Fertilizer 8-15-36 at 1–3 g per plant in 1 gallon every 10 days. Pots have no soil reserve, so add Cal-Mag Plus separately on RO or distilled water (sodium-softened water is not suitable for irrigation), and flush each pot monthly with three times its volume of plain water[6].
What fertilizer is best for basil?
Basil is cut hard and often, so it does well on a moderate-nitrogen, high-potassium leafy formula such as Lettuce Fertilizer 8-15-36: 1 g per plant while young, 3 g in active growth, in 1 gallon of water every 10 days. In hydroponics, 0.8 g per plant at transplant and 1.5 g established, EC at the low end of 1.2–1.6, pH 5.6–6.2 by stage (see the hydroponic table). Basil is sensitive to low magnesium and iron[5], so keep Cal-Mag Plus in the program and pH under 6.5, and harvest before it flowers[2].
Should I fertilize rosemary and thyme the same as basil?
No. Rosemary and thyme come from lean, dry ground and lose flavor and aroma intensity when fed like a leafy crop; over-fertilizing them also encourages root and stem rot[1]. Give them 11-11-40 at 1.5 g per plant monthly, nothing in winter, and prioritize drainage. In a compost-amended bed, one light feeding at the start of the season is often all they need.
Can I use Pepper & Herb 11-11-40 on basil, cilantro, and parsley?
You can, but it is not the first choice. Greenway product guidance sends soft leafy herbs to Lettuce Fertilizer 8-15-36, which is fed in smaller, more frequent doses that match a cut-and-come-again harvest. If 11-11-40 is what you have, use the woody-herb rate (1.5 g per plant) on the lower side and add a light nitrogen companion during heavy cutting cycles.
Can you over-fertilize herbs?
Yes, and it is more common than under-fertilizing, especially in containers and with the woody group. It shows as lush, soft growth that wilts easily, brown leaf tips from salt injury, and weaker aroma. Flush the container with three times its volume of plain water[6], skip the next one or two feedings, and resume at a lower rate.
How often should you fertilize herbs?
Woody Mediterranean herbs: monthly during active growth, never during winter dormancy. Soft leafy herbs in containers: every 10 days while they are being cut and regrowing. Indoor herbs in window light: half the rate on a longer interval — every 6–8 weeks for woody herbs, every 2–3 weeks for soft herbs. Hydroponic systems: replace the solution every 1–2 weeks and top up with plain water in between[5].
Are there organic fertilizer options for herbs?
Yes. For woody herbs, compost plus Kelp Meal 2-0-4 (repackaged from OMRI Listed® Ascophyllum nodosum) at planting is usually enough. For soft herbs, add Blood Meal 13-0-0 — the 40 lb bag is repackaged from OMRI Listed® material — at 1 tsp per 6-inch pot or 1–2 tsp per bed plant, side-dressed monthly while you are cutting — dose per plant rather than broadcasting a bed rate, and work to a soil test. Both meals release through soil microbes, so they work in soil and potting mix but not in hydroponics.
Why are the leaves on my basil turning yellow?
Look at where it starts. Older, lower leaves first usually means nitrogen is running short in a heavily cut plant — or that the roots are waterlogged, so check the media first. Yellow new leaves with green veins point to iron or manganese locked out by high pH or high-alkalinity water; correct pH before adding chelated iron. Yellowing between the veins on older leaves points to magnesium, which basil is sensitive to[5]; Cal-Mag Plus supplies it.
About this guide
Review & sources
Reviewed by Amir Tajer, B.S.M.E., QAL — Co-Owner & Technical Director, Greenway Biotech, Inc. Reviewed against University of Maryland, Clemson, UF/IFAS, and UMass Extension guidance and University of Florida hydroponic basil research (HortScience, 2020). Last updated August 24, 2026. Disclosure: Greenway Biotech manufactures, packages, or sells the Pepper & Herb Fertilizer 11-11-40, Lettuce Fertilizer 8-15-36, Cal-Mag Plus, Chelated Iron EDTA, Blood Meal, and Kelp Meal discussed in this guide (the meals are repackaged, not manufactured); organic alternatives and situations where these products are not the right fit are covered above. Application rates are Greenway product guidance as published on the live product pages, retrieved August 24, 2026.
Sources
- Care of Herbs and Starting Herbs from Seed — University of Maryland Extension
- Herbs (HGIC 1311) — Clemson University Home & Garden Information Center
- Understanding and Applying Chelated Fertilizers Effectively Based on Soil pH (HS1208) — UF/IFAS Extension
- Water Quality: pH and Alkalinity — UMass Extension Greenhouse Crops and Floriculture Program
- Solis-Toapanta, Fisher & Gómez (2020). Growth Rate and Nutrient Uptake of Basil in Small-scale Hydroponics. HortScience 55(4):507–514 — University of Florida IFAS (open-access PDF hosted by Purdue Extension; DOI 10.21273/HORTSCI14727-19)
- Mineral and Fertilizer Salt Deposits on Indoor Plants — University of Maryland Extension
