Nutrient Timing, Proportions, Forms, and Micronutrient Management for Outdoor and Indoor Growing

1. Macronutrients and Their Roles

– Nitrogen (N): Drives leafy growth and stem development. Crucial early but must be reduced at flowering.
– Phosphorus (P): Encourages strong root systems, early vigor, and flower initiation.
– Potassium (K): Regulates water, disease resistance, fruit fill, and flavor quality.
– Calcium (Ca): Essential for cell walls and preventing blossom end rot.
– Magnesium (Mg): Central component of chlorophyll.
– Sulfur (S): Involved in protein and enzyme synthesis.

2. Micronutrients and Their Roles

– Iron (Fe): Key for chlorophyll formation. Deficiency causes interveinal yellowing.
– Boron (B): Needed for flowering and fruit set.
– Zinc (Zn): Affects growth hormone production and leaf size.
– Manganese (Mn): Assists enzyme function and photosynthesis.
– Copper (Cu): Needed in tiny amounts for root health.
– Molybdenum (Mo): Required for nitrogen metabolism.
– Chlorine (Cl): Involved in water transport, rarely deficient.

3. Fertilizer Timing Table by Growth Phase

Phase | Weeks | Target NPK Ratio | Notes
Germination | 0–2 | None or 1-1-1 (dilute) | Fish emulsion or seedling-specific mix
Early Veg | 2–4 | 3-1-2 or 20-10-10 | Promotes leaves and roots
Mid Veg | 4–6 | 3-1-2 or 10-5-5 | Pushes mass without overfeeding
Pre-Flower | 6–8 | 2-1-2 or 5-10-10 | Reduces N, encourages blooms
Flowering | 8+ | 1-2-2 or 3-12-6 | Maximizes fruiting, strengthens stems
Fruiting | 10+ | 2-4-8 or 4-6-10 + CaMg | Keep K and Ca high, lower N

4. Indoor Potted Plant Schedule Example

Medium: Coco/perlite with inert starter
– Weeks 0–2: Fish emulsion or CalMag (1 mL/L)
– Weeks 2–5: 20-10-20 + CalMag every 7 days
– Weeks 6–8: Bloom fertilizer 3-12-6; switch CalMag to foliar weekly
– Weeks 9–12+: Potassium-heavy feed 2-4-8 + Calcium nitrate (root zone or foliar) every 5–7 days
– Leach every 3 weeks to avoid salt buildup

5. Outdoor Soil-Grown Plant Schedule

– Pre-Plant: Compost, 2 Tbsp bone meal, 1 tsp Epsom salts per hole
– Week 2: Water-in with 10-10-10 (1 tbsp/gal)
– Weeks 3–6: 5-5-5 or 10-5-5 every 2 weeks
– Weeks 7+: Switch to 4-6-10 or tomato-tone + potassium sulfate monthly
– Add CalMag or gypsum monthly for calcium
– Mulch and top-dress with worm castings monthly

6. Micronutrient Supplementation

– Foliar options: Seaweed extract, kelp meal, chelated iron, CalMag sprays
– Soil options: Azomite, greensand, micronutrient mixes (e.g., Micropak)
– Signs of need: Pale new growth (iron), flower drop (boron), stunted tips (zinc)

7. Example Brands

– Base Nutrients: Jack’s 20-10-20, Dyna-Gro Foliage Pro, FoxFarm Grow Big / Tiger       Bloom
– Calcium & Magnesium: CalMag Plus, Dolomite Lime (soil), Calcium Nitrate (hydroponic)
– Micronutrient Blends: Micropak, CSM+B, Earth Juice MicroBlast
– Organic: Down to Earth 4-4-4, Tomato-tone, Neptune’s Harvest
– Time-Release: Osmocote Plus (3–4 month feed), Jobe’s Organic Tomato Spikes

8. Best Practices

– pH for absorption: 6.0–6.8 (soil), 5.8–6.2 (coco)
– Water thoroughly before applying fertilizer
– Avoid feeding during drought stress or heatwaves
– Adjust ratios by observation—yellowing or blossom drop often signals a deficiency
– Do not rely solely on NPK—micronutrient management is key to avoiding hidden deficiencies