Lettuce & Leafy Greens — Fertilizer Guide
The best fertilizer for lettuce is the one that matches how you grow.
There is no single fertilizer that is best for every lettuce planting. In soil, the right choice starts with a soil test. In containers and hydroponics, a fully water-soluble program with managed strength (EC) and pH typically works best. For growers who want one measurable, water-soluble base fertilizer for lettuce and other label-listed leafy greens, Greenway Biotech's Lettuce Fertilizer 8-15-36 is a strong fit — this guide covers exactly when it is, when it isn't, and the verified rates for soil, containers, and hydroponic systems.
Find your growing method Jump to application rates36%
Soluble potash (K₂O) for water regulation and crop quality
3g
Labeled soil rate per plant, every 4–6 weeks
2.0EC
Never exceed in hydroponic lettuce — under 1.8 during head fill
0Ca
Calcium in the bag by design — supply it separately
The Science
What Nutrients Does Lettuce Need?
Lettuce is grown for its leaves, not flowers or fruit — and that shapes its entire nutritional profile.
Lettuce benefits from a steady, moderate supply of all three primary macronutrients across its short life cycle, plus secondary nutrients and a complete micronutrient package. Because the harvested product is the leaf itself, quality traits like crispness, color, and post-harvest holding matter as much as raw growth rate.
Nitrogen (N): Leaf Development Without Excess
Nitrogen drives chlorophyll production and the rapid cell division lettuce is known for. Too little, and plants grow slowly with pale older leaves. Too much — especially in warm weather — and tissue becomes overly succulent, flavor turns bitter, and leaf nitrate levels climb. A moderate nitrogen supply, such as the 8% total N in an 8-15-36 grade (7.5% nitrate, 0.5% ammoniacal per the registered label)[1], can support healthy leaf development without those downsides. For a deeper look, see our article on the function of nitrogen in plants.
Available Phosphate (P₂O₅): Roots, Membranes, and Energy Transfer
Phosphorus — listed on fertilizer labels as available phosphate (P₂O₅) — supports root establishment, cell membrane integrity, and energy transfer (ATP) throughout the plant. Lettuce needs adequate phosphate, but the correct amount depends on what your soil already holds or what your complete hydroponic recipe supplies. Many established garden soils already contain sufficient phosphorus; University of Minnesota Extension recommends a low- or no-phosphorus fertilizer unless a soil test specifically calls for more[3]. See the function of phosphorus in plants for more detail.
Potassium (K₂O): Water Regulation, Stress Tolerance, and Quality
Potassium — listed on labels as soluble potash (K₂O) — regulates water movement through the plant via stomatal control, is required for the activity of dozens of enzyme systems, and supports cell turgor in a crop that is mostly water. Field research on lettuce shows that correcting a potassium shortfall can improve growth and certain quality traits, with a nonlinear response — more potassium is not automatically better, and the right rate depends on the soil or the complete nutrient solution[4]. Cultivar, temperature, irrigation consistency, and harvest timing also shape final quality. For more, see our guide on the function of potassium in plants.
Secondary Nutrients: Calcium, Magnesium, and Sulfur
Calcium, magnesium, and sulfur are secondary macronutrients — needed in smaller amounts than N-P-K but in far larger amounts than micronutrients. Calcium is especially consequential for lettuce: it is the nutrient at the center of tip burn, the most common disorder in hydroponic production (covered in its own section below). Magnesium sits at the center of the chlorophyll molecule; a shortfall shows as interveinal yellowing on older leaves and, in hydroponics, is usually addressed through a Cal-Mag product or Epsom Salt guided by a water test.
Micronutrients and Chelation: What pH Actually Does
Iron, manganese, zinc, copper, boron, and molybdenum are all required in small amounts. Availability is pH-dependent, but in different directions: as pH rises above roughly 6.5, iron and manganese in simple mineral form increasingly precipitate and become unavailable — the classic high-pH lockout behind interveinal chlorosis on young leaves. At excessively low pH the problem reverses: iron and manganese become more soluble, and toxicity rather than lockout becomes the risk.
Chelation improves solubility and reduces precipitation, but the useful range depends on the chelating agent. EDTA-chelated iron, manganese, zinc, and copper — the forms in 8-15-36[1] — hold up well in mildly acidic to near-neutral systems, which covers the pH ranges lettuce is grown in. Where iron deficiency persists under strongly alkaline conditions, correct pH and alkalinity where practical, or step up to a chelate built for higher pH such as Chelated Iron DTPA (with EDDHA-type chelates as the option of last resort for persistently alkaline soils). Our comparison of sulfate vs. chelated fertilizers covers the chemistry in depth.
🔬 Did You Know?
An NPK grade describes the bag, not the plant. At the labeled soil rate of 3 grams of 8-15-36 per plant, each application delivers about 0.24 g nitrogen, 0.45 g available phosphate (P₂O₅), and 1.08 g soluble potash (K₂O). The nutrient dose a plant actually receives depends on both the percentage and how much you apply — which is why the rate tables below matter more than the three numbers on the front of any bag.
The Direct Answer
What Is the Best Fertilizer for Lettuce?
For most soil growers, the best fertilizer for lettuce is whichever formula supplies what a current soil test says is missing — often that means moderate nitrogen with little or no additional phosphate or potash[3]. For container and hydroponic growers, a fully water-soluble, high-potash base fertilizer with chelated micronutrients typically works best, managed to a target solution strength (EC) and pH.
Greenway Biotech Lettuce Fertilizer 8-15-36 is built for that second job: a 100% water-soluble base fertilizer registered for lettuce, kale, spinach, Swiss chard, arugula, bok choy, microgreens, and other leafy crops listed on its CDFA-registered label[1]. It supplies 8% nitrogen, 15% available phosphate (P₂O₅), 36% soluble potash (K₂O), and six micronutrients — iron, manganese, zinc, and copper as EDTA chelates, with boron and molybdenum in highly available mineral form. It contains no calcium or magnesium by design (concentrated calcium and phosphate form insoluble calcium phosphate together), so those nutrients must come from your source water or a companion product. It is made in the USA at our Madera, CA facility and independently lab-tested for heavy metals[6].
When 8-15-36 Fits — and When to Choose Another Approach
| 8-15-36 tends to be a good fit when… | Choose another approach when… |
|---|---|
| You want one fully soluble base fertilizer for a label-listed leafy crop | A soil test shows phosphorus (P₂O₅) or potassium (K₂O) is already high — feed only what the test calls for |
| You grow in containers or hydroponics and can measure grams, pH, and EC | You want a single product that already contains calcium and magnesium |
| Your calcium plan is settled — source water, Cal-Mag Plus, or Calcium Nitrate | You cannot measure or control solution strength reliably |
| You value a documented guaranteed analysis, registered label, and lab testing | You want a certified-organic-only program — see our organic fertilizer guide instead |
How 8-15-36 Compares to Other Formula Types
| Formula Type | Best Suited For | Consideration |
|---|---|---|
| ⭐ 8-15-36 specialty (this guide) | Hydroponics, containers, and quality-focused soil growers | Chelated micronutrients included; no calcium or magnesium — pair with a calcium source |
| Balanced (20-20-20 or similar) | General vegetable gardens where lettuce is one of many crops | Often more phosphate than a tested soil needs; may lack micronutrients |
| Organic amendments (Blood Meal, Bone Meal) | Building long-term soil fertility pre-plant | Slow, microbe-dependent release; not suitable for hydroponic reservoirs |
Decision Framework
Choose by growing method, then pick the rate.
| Your Situation | Recommended Approach |
|---|---|
| Garden soil, no current soil test | Get a soil test first ($15–30 at most extension labs)[3]; until then, use the labeled 3 g per plant rate and skip extra phosphate or potash products |
| Soil test shows high P₂O₅ or K₂O | Reduce or skip those nutrients; a nitrogen-only source such as Blood Meal 13-0-0 may cover the gap |
| ⭐ Hydroponic system (most common use for this product) | 8-15-36 as the base nutrient; account for calcium and magnesium from water or companion products; never exceed 2.0 EC |
| Containers, coco coir, or perlite | Per-plant liquid feeding on the container schedule below; inert media buffer nothing, so treat calcium like a hydroponic grower would |
| Tip burn appearing on inner leaves | Work through the tip burn section below — check EC, airflow, and moisture before reaching for more calcium |
| Microgreens or baby leaf | Cotyledon-stage microgreens (7–14 days): quarter-strength after cotyledons emerge, one feeding is usually enough. Baby leaf (3–4 weeks): 50–75% strength every 5–7 days |
| Other leafy greens (kale, spinach, chard, bok choy) | Same product, same method-based rates — these crops appear on the registered label[1] |
Soil & Containers
How Often Should You Fertilize Lettuce?
Rates below match the CDFA-registered product label (updated March 25, 2025) and the live Lettuce Fertilizer 8-15-36 product page. Weight first; volume approximations second.
In-Ground and Raised Beds (Labeled Rate)
The registered label directs 3 grams (approximately ½ teaspoon) of 8-15-36 per plant every 4–6 weeks, starting at planting and ending just before first harvest[1]. Delivered as a liquid feed, that works out to:
Mix: 12 grams (approximately 1 tablespoon) per gallon of water
Apply: 1 quart (4 cups / 32 fl oz) of solution per plant, at the base — not over the foliage
Dose received: 3 grams per plant — the labeled rate
Coverage: One gallon of mixed solution feeds 4 plants
Frequency: Every 4–6 weeks during active growth
For larger beds fed by area rather than per plant, the product page's bed program is: 1 lb per 100 sq ft worked in pre-plant with compost; then 0.25 lb (~113 g) per 100 sq ft side-dressed every 2 weeks for cut-and-come-again greens, or a single side-dress at heading for head lettuce; or 0.5 lb per 100 gallons of irrigation water weekly through drip. Because area rates are set per 100 sq ft, plant count doesn't change the amount. Confirm bed rates against a current soil test[3].
Containers and Pots (Per-Plant Program)
Containers are fed per plant, with the fertilizer amount stepping up by stage while the water volume stays at one gallon per plant. At the active-growth stage:
Mix: 3 grams (a generous ½ teaspoon) into 1 gallon of water
Apply: The full gallon to one plant, onto already-moist media, then water in with plain water
Dose received: 3 grams per plant
Coverage: One gallon of mixed solution feeds 1 container plant
Frequency: Every 10 days; flush containers with plain water once monthly to reset salts
| Stage | 8-15-36 per plant | Notes |
|---|---|---|
| At potting | ½ tsp per gallon of potting mix, blended in | Top-dress again at 3 weeks |
| Seedling / young | 1 g (a scant ¼ tsp) | Begin once first true leaves develop |
| ⭐ Active growth | 3 g (a generous ½ tsp) | The workhorse rate for most of the crop cycle |
| Mature / large head | 5 g (approximately 1 tsp) | Reduce feeding 2 weeks before harvest |
Pair container feeding with Cal-Mag Plus 2-0-0 at about 5 ml of prepared stock per plant between fertilizer feedings to help keep calcium supplied to fast-growing tissue.
Pre-Plant Soil Building
Where a soil test shows genuine gaps, slow-release organics build baseline fertility ahead of transplanting: Blood Meal 13-0-0 for nitrogen (release slows notably in soils below 55°F, so early-spring plantings often benefit from a soluble feed while it activates) and Bone Meal 3-15-0 only where the test shows phosphorus is actually limited. Our guide to the best fertilizers for a vegetable garden covers broader amendment strategy.
Foliar Feeding (Supplemental Only)
The label's foliar direction is 1 gram per plant every 1–2 weeks, beginning once first true leaves have developed[1]; the product page expresses the same job as a spray concentration of roughly 1.7–3.4 g per gallon of finished spray depending on purpose, never exceeding 3.4 g per gallon. Spray only in early morning or late afternoon, never on heat-stressed plants, and stop all foliar feeding 7 days before harvest — fertilizer residue on leaves destined for the salad bowl is unacceptable.
⚠️ Keep Fertilizer Solution Off the Leaves
For root feeding, apply solution at the base of the plant. Lettuce foliage is delicate and can develop burn spots where fertilizer solution sits on it, especially in sun or heat. Foliar feeding is a separate, deliberately dilute technique with its own rates — not a side effect of sloppy watering.
Timing Across the Season
Most lettuce reaches harvest in 45–80 days, so the feeding window is short — typically just one or two applications after the initial planting-time feed. Lettuce is a cool-season crop that grows best with nights near 50°F and days below roughly 70°F; bolting risk rises with sustained warm spells, long days, and intense light, and University of Minnesota Extension notes that multiple days above about 75°F can trigger flowering in susceptible cultivars[3]. Heat tolerance varies considerably by variety, so in warm regions lean on Batavia and Summer Crisp types and time plantings for your local shoulder seasons rather than relying on a single universal temperature cutoff.
Hydroponics
How to Fertilize Hydroponic Lettuce
In hydroponics, the plant receives exactly what the complete solution contains — nothing more. Think in terms of the whole recipe, not one bag.
Lettuce's fast growth, compact roots, and tolerance for close spacing make it one of the most popular crops for NFT, DWC, Kratky, and ebb-and-flow systems. Penn State Extension's approach to hydroponic recipes is the right mental model: every ingredient contributes nutrients (calcium nitrate adds nitrogen along with calcium; magnesium sulfate adds sulfur along with magnesium), source-water minerals count toward the total, and calcium must be kept out of concentrated contact with phosphates and sulfates[5]. For system setup basics, see how to build your own hydroponic garden.
The Complete Stack
Base nutrient: Lettuce Fertilizer 8-15-36 — NPK plus six micronutrients; contains no calcium or magnesium.
Calcium (and magnesium): Cal-Mag Plus 2-0-0 as the standard companion, or Calcium Nitrate 15.5-0-0 on RO or soft water — noting they are not interchangeable: Calcium Nitrate adds nitrate nitrogen along with calcium, Cal-Mag adds magnesium and some nitrogen, and either raises final EC.
Source water: Test it. Water above roughly 30 ppm calcium already carries part of the requirement; above about 80 ppm, Cal-Mag may not be needed at seedling and vegetative stages at all. Add calcium and magnesium at rates your water test justifies, not by default[5].
Hydroponic Rates (Per Plant)
Everything in this table is per plant — multiply each column by your plant count, mix into the reservoir, then top up water until the meter reads the target EC. The EC column is the final measured value after all components are mixed. Cal-Mag amounts are ml of prepared stock.
| Stage | 8-15-36 | Cal-Mag Plus stock | Calcium Nitrate (RO/soft water) | Water per plant | Final EC | pH |
|---|---|---|---|---|---|---|
| Seedling / transplant | 0.8 g | 3 ml | — | 0.8–0.9 gal | 0.8–1.0 | 5.8–6.2 |
| ⭐ Vegetative | 1.5 g | 6 ml | 0.6–1 g (optional) | 0.8–0.9 gal | 1.2–1.6 | 5.6–6.0 |
| Mature / harvest | 1.7 g | 8 ml | 1–1.7 g (head fill) | 0.8–0.9 gal | 1.4–1.8 max | 5.5–6.0 |
Worked example — 60 plants in vegetative growth on RO water: 60 × 1.5 g = 90 g of 8-15-36, plus 60 × 6 ml = 360 ml Cal-Mag stock, plus 60 × 0.6–1 g = 36–60 g Calcium Nitrate (optional at this stage), into roughly 50 gallons of water — then top up until the reservoir measures 1.2–1.6 EC. Replace recirculating solutions every 7–14 days, or sooner if EC drifts more than about 0.5 mS/cm between top-offs. These figures are starting targets: reduce concentration in heat, low airflow, or whenever tip burn recurs, and let your calibrated meter — not the table alone — make the final call.
Mixing Order (Non-Negotiable)
- Fill to full water volume first. Concentration errors compound when you dose into a half-full reservoir.
- Dissolve Calcium Nitrate completely (if using, on RO/soft water), with the pump running.
- Add Cal-Mag Plus stock and allow full circulation.
- Add pre-dissolved 8-15-36 last, from the far side of the reservoir.
- Adjust pH, then verify final EC with a calibrated meter.
⚠️ Never Combine Calcium and Phosphate Concentrates
Concentrated calcium and phosphate react to form insoluble calcium phosphate — locking out both nutrients and clogging lines and emitters. Keep them in separate stock containers, pre-dissolve each independently, and only let them meet in the fully diluted reservoir[5]. This is also why 8-15-36 contains no calcium: with 15% available phosphate (P₂O₅) in the bag, calcium has to travel separately.
🔬 Did You Know?
Hydroponic lettuce often reaches harvest faster than soil-grown lettuce — but the speed comes from the whole controlled environment, not just dissolved nutrients. Managed light, temperature, oxygenated root zones, spacing, and continuous water availability each contribute. Under comparable environmental stress, hydroponics loses much of its head start. More in our guide to the best fertilizers for hydroponics.
The #1 Lettuce Disorder
Tip burn is a calcium transport problem.
Tip burn — the brown, crispy margins on young inner leaves — is a localized calcium deficiency in rapidly expanding tissue, and it frequently develops even when the root zone contains plenty of calcium. UC IPM's assessment is blunt: tip burn is rarely the result of low soil calcium; the usual drivers are water stress, low evapotranspiration, rapid growth, and head formation, which shelters inner leaves from the transpiration stream that carries calcium[2]. Foliar calcium can help exposed leaf tissue it directly contacts, but it cannot reach the susceptible tissue inside a forming head in time — and in California lettuce districts, adding calcium to soil that already has enough is generally ineffective[2].
Note where the damage sits: on the youngest leaves at the center of the head, while the outer wrapper leaves stay clean. That location is the diagnostic — salt burn and heat scorch hit the exposed outer margins first, so if the browning is on the outside of the plant, you are looking at a different problem with a different fix.
What that means in practice: first verify the complete program supplies adequate calcium (source water plus companion products), then manage the transport side — consistent moisture, final EC under 1.8 during head fill and never above 2.0, real air movement across the canopy, moderate growth rate, sensible spacing, and cultivar choice, since susceptibility varies widely[2]. Adding more calcium on top of an adequate program will not fix tip burn when transport is the limiting factor.
Beyond Lettuce
One label, the whole leafy family.
The registered label lists lettuce alongside kale, microgreens, broccoli, collard greens, spinach, cabbage, beet greens, watercress, Swiss chard, arugula, endive, bok choy, and turnip greens[1] — so the same method-based rates above apply across the family. Two scaled exceptions from the product page: baby leaf production (3–4 weeks to harvest) runs at 50–75% of standard concentration every 5–7 days, and microgreens (7–14 days) run at 25% concentration after cotyledons emerge, where a single feeding is usually sufficient because early growth draws mostly on seed reserves. Lettuce varieties themselves differ more in timing than nutrition: loose-leaf types mature fastest (roughly 40–55 days) and carry the highest hydroponic tip burn risk, romaine runs 60–80 days and appreciates consistent nitrogen across its longer season, and dense-heading butterhead and crisphead types deserve the most airflow and EC discipline during head fill.
Diagnosis Before Treatment
Lettuce problems: confirm first, then correct.
Leaf symptoms overlap. Before adding any nutrient, check moisture and roots, check temperature and airflow, measure pH and EC, and review what was recently applied.
The fastest split in the table below is which leaves are yellow. Nitrogen is mobile, so the plant strips it from the oldest leaves first — they yellow uniformly, veins included. Iron is immobile, so a shortfall shows on the newest growth as yellow tissue between veins that stay green. Get that one observation right and half the table rules itself out.
| Symptom | Possible Causes | How to Confirm | Corrective Action |
|---|---|---|---|
| Pale yellow older leaves, bottom up | Nitrogen deficiency; natural senescence; saturated or damaged roots; low EC | Check roots and drainage first; in hydro, measure EC; N shortfall shows as uniform yellowing that climbs the plant | If confirmed, feed at the standard rate for your method; recheck new growth in 1–2 weeks. Overlapping look-alikes in our guide to why leaves turn yellow |
| ⭐ Brown, crispy inner leaf tips | Tip burn — calcium transport failure[2] | Inner young leaves affected while outer leaves look fine; EC above 1.8; still air; recent growth spurt | Drop EC below 1.8, improve canopy airflow, steady the moisture, and verify the program's calcium; see the tip burn section above |
| Yellow between veins on young leaves | Iron or manganese lockout at high pH; high-alkalinity water; root stress | Measure pH of soil or solution — lockout is likely above ~6.5; check alkalinity of source water | Correct pH first; if deficiency persists, supplement with Chelated Iron EDTA or Chelated Manganese EDTA |
| Scorched brown margins on outer leaves | Fertilizer burn or salt buildup; heat or water stress; drift injury | White crust on media or container rim; recent over-application; hot dry spell in the log | Flush soil or media with plain water; resume at half rate; in hydro, dilute the reservoir to target EC |
| Small, cupped, slow leaves | General underfeeding or low EC; cold media; root restriction; potassium shortfall is only one of several candidates | Measure EC and check root health before blaming any single nutrient; confirm with a soil or tissue test if it persists | Correct the confirmed cause; where a test shows potassium (K₂O) is genuinely low in soil, Potassium Sulfate 0-0-53 is a targeted supplement |
| Purpling on stunted seedlings | Cold-soil phosphorus uptake slowdown; cultivar pigmentation; root injury | Check soil temperature — below ~55°F, P uptake slows even in P-rich soil; some varieties are simply red | Warm the soil before transplanting and use a soluble feed for immediate availability; do not add phosphate to warm, tested soil |
| Rapid bolting (flower stalk) | Heat, long days, and high light — not a nutrient problem[3] | Multiple days above ~75°F in the forecast log; long-day season; bitter flavor developing | Switch to heat-tolerant Batavia or Summer Crisp types, use partial shade, and time plantings for cooler windows — do not change fertilizer |
💡 Document Before You Treat
Photograph symptoms before changing anything. If the issue doesn't improve within 10–14 days of a confirmed correction, send photos with your soil, water, or reservoir readings to your local cooperative extension office — California growers can access UC Cooperative Extension diagnostics at low or no cost. Our guide to essential micronutrients covers visual identification across vegetable crops in more depth.
Build the Program
The base, plus what completes it.
Lettuce Fertilizer 8-15-36
Water-soluble NPK plus six micronutrients for every label-listed leafy crop. CDFA registered, lab tested.
Essential pairCal-Mag Plus 2-0-0
Calcium and magnesium for tip-burn-prone leafy crops — the standard hydroponic companion.
RO waterCalcium Nitrate 15.5-0-0
Calcium with a nitrate boost for RO or soft-water reservoirs, especially at head fill.
Test-confirmedPotassium Sulfate 0-0-53
Targeted potassium (K₂O) for soils a test shows are genuinely short.
Common Questions
Lettuce fertilizer, answered.
What is the best NPK ratio for lettuce?
There is no single best ratio for every planting. In soil, the right ratio depends on a current soil test — many garden soils need little or no added phosphate. In containers and hydroponics, a high-potash, moderate-nitrogen grade such as 8-15-36 works well as the base of a complete program, because leaf quality and water regulation lean on potassium (K₂O) while excess nitrogen degrades flavor, shelf life, and leaf nitrate levels. The dose delivered matters more than the numbers on the bag.
How often should I fertilize lettuce in a garden bed?
The registered label rate is 3 grams (about ½ teaspoon) per plant every 4–6 weeks, from planting until just before first harvest. Because lettuce matures in 45–80 days, that usually means one or two feedings per planting after the initial dose. Containers run a different program: per-plant staged feeding every 10 days with a monthly plain-water flush.
Can I use the same fertilizer for hydroponic and soil lettuce?
Yes — a fully water-soluble product like 8-15-36 works in both, at different rates for each method. In hydroponics you also take on the jobs soil quietly does for you: supplying calcium and magnesium (from source water or companion products), and holding pH and EC in range. Slow-release organic fertilizers are not suitable for hydroponic reservoirs.
Why do my hydroponic lettuce leaves have brown tips?
That's tip burn — a localized calcium deficiency in fast-growing inner leaves, usually caused by transport failure rather than too little calcium in the reservoir. Verify the complete program supplies calcium, then fix transport: keep final EC under 1.8 during head fill, improve air movement across the canopy, keep moisture consistent, and choose less-susceptible cultivars. Pouring in extra calcium rarely fixes it on its own.
Does Lettuce Fertilizer 8-15-36 contain calcium?
No, by design. Concentrated calcium and phosphate form insoluble calcium phosphate, and this formula carries 15% available phosphate (P₂O₅). Supply calcium separately — Cal-Mag Plus or Calcium Nitrate — at a rate your water test supports, and never combine calcium and phosphate concentrates before full dilution.
Can I use lettuce fertilizer on spinach, kale, and other leafy greens?
Yes — kale, spinach, Swiss chard, arugula, collard greens, cabbage, bok choy, endive, watercress, beet greens, turnip greens, broccoli, and microgreens all appear on the registered label. Use the same method-based rates, scaling down to 50–75% strength for baby leaf and 25% for microgreens after cotyledons emerge.
My lettuce has yellow older leaves. Is that a nitrogen deficiency?
Possibly — nitrogen is mobile, so a shortfall shows first as uniform yellowing on older leaves that climbs the plant. But saturated roots, natural senescence, and low solution strength look similar, so check roots, drainage, and EC before feeding. Yellowing between green veins on young leaves points instead to iron or manganese lockout from high pH — correct the pH first rather than adding more fertilizer.
About This Guide
Review & sources
Reviewed by Amir Tajer, B.S.M.E., QAL — Co-Owner & Technical Director, Greenway Biotech, Inc. Last updated: August 12, 2026.
Sources consulted: the CDFA-registered Lettuce Fertilizer 8-15-36 product label (updated March 25, 2025), UC Statewide IPM Program, University of Minnesota Extension, Penn State Extension, and peer-reviewed research in Agronomy. Application rates in this guide are drawn from the registered label and the live product page, verified August 2026.
Disclosure: Greenway Biotech manufactures the Lettuce Fertilizer 8-15-36 discussed in this guide. Its limitations, soil-test considerations, and alternative approaches — including organic amendments and balanced fertilizers — are covered above.
Sources:
- Lettuce Fertilizer 8-15-36 — CDFA-Registered Product Label, updated 03-25-2025 (PDF)
- Tipburn / Lettuce — UC Statewide IPM Program, UC ANR
- Growing Lettuce, Endive and Radicchio in Home Gardens — University of Minnesota Extension
- Hong et al., Effects of Nitrogen, Phosphorus, and Potassium Applications on the Growth, Yield, and Quality of Lettuce — Agronomy 12(10):2477, 2022
- Hydroponics Systems: Calculating a Nutrient Solution Recipe — Penn State Extension
- Lettuce Fertilizer 8-15-36 — Independent Heavy Metal Analysis, AgroLab, Dec 2024 (PDF)