Fertilizers

NPK stands for nitrogen (N), phosphorus (P), and potassium (K) — the three primary macronutrients plants need in the largest quantities. The three numbers on every fertilizer bag (e.g., 10-10-10 or 46-0-0) are the guaranteed analysis: the percentage by weight of available N, P₂O₅ (phosphate), and K₂O (potash) in that order. A bag labeled 21-0-0 contains 21% nitrogen and no phosphorus or potassium. A 4-18-38 label means 4% nitrogen, 18% phosphate, and 38% potash. Note that P and K values are expressed as P₂O₅ and K₂O rather than elemental phosphorus and potassium — this matches how soil fertility is reported on fertilizer labels industry-wide. Secondary nutrients (calcium, magnesium, sulfur) and micronutrients (iron, zinc, manganese, copper, boron, molybdenum) are listed separately when present in guaranteed amounts.

Not all water-soluble fertilizers are approved for certified organic production — most synthetic water-solubles (Urea, Calcium Nitrate, MAP, MKP, Potassium Sulfate) are not OMRI listed and are not permitted in certified organic programs. However, some water-soluble products derived from organic sources may qualify. If organic certification matters for your operation, check individual product pages for OMRI status and consult your certifying agency. For home gardens without certification requirements, synthetic water-solubles are widely used alongside organic amendments.

Soil application delivers nutrients to the root zone — either as a dry broadcast/incorporation or dissolved in irrigation water (fertigation). Nutrients are taken up through the root system over time. Foliar feeding involves spraying a dilute fertilizer solution directly onto leaves for rapid absorption through the leaf surface — useful for correcting acute deficiencies quickly or supplementing during high-demand growth stages. Foliar feeding is not a substitute for healthy soil nutrition; it's most effective as a targeted supplement. Only water-soluble fertilizers should be used for foliar applications. Apply in the early morning or evening when temperatures are below 85°F and foliage is dry — never during heat stress or midday sun.

Most nutrient deficiencies produce visible symptoms on leaves — the pattern tells you which nutrient is involved. Yellowing that starts on older, lower leaves typically indicates nitrogen or magnesium deficiency (mobile nutrients). Yellowing between leaf veins on young, new leaves (interveinal chlorosis) is the classic sign of iron, zinc, or manganese deficiency (immobile micronutrients). Stunted new growth with short internodes suggests zinc deficiency. Purple or reddish leaf undersides can indicate phosphorus deficiency, especially in cold soils. A soil test is the most reliable way to confirm which nutrients are genuinely deficient before purchasing amendments. Our free deficiency diagnosis tool walks you through symptom location, pattern, pH, and growing method to narrow it down.

Yes. Products in this collection are CDFA registered and manufactured under quality-controlled conditions at our Madera, California facility. Organic products are derived from natural plant, animal, or mineral sources. Synthetic fertilizers are manufactured to food and agricultural grade standards. All products are third-party tested for heavy metals — results are available on our Heavy Metal Analysis page. Follow recommended application rates on individual product pages. For edible crops, avoid applying any fertilizer directly to foliage within 2 weeks of harvest.

Yes — free shipping on all orders over $100 to the continental United States. All products are shipped from our Madera, California facility. For questions about your order, contact us at questions@greenwaybiotech.com or call (562) 351-5168, Monday–Friday 7AM–5PM PST.