DISCLAIMER: Cannabis cultivation is illegal in many jurisdictions. This content is provided for educational purposes only. Always research and comply with your local laws and regulations before cultivating cannabis. Unauthorized cultivation may result in legal penalties.
¶ Nutrients & Feeding
Cannabis plants require a balanced diet of macro and micronutrients to grow vigorously and produce dense, resinous flowers. Understanding nutrient requirements, managing pH, and recognizing deficiency symptoms are essential skills for every cultivator.
¶ Macronutrients
Cannabis requires three primary macronutrients in large quantities, identified by the NPK ratio on all fertilizer labels.
| Nutrient | Symbol | Primary Role | Deficiency Signs | Excess Signs |
|---|---|---|---|---|
| Nitrogen | N | Leaf and stem growth; chlorophyll production | Older leaves yellow (bottom-up); slow growth; weak stems | Dark green leaves; clawing; brittle growth; nutrient burn |
| Phosphorus | P | Root development; flowering; energy transfer (ATP) | Purple/dark leaves; slow growth; poor bud development; red stems | Iron and zinc lockout; stunted growth |
| Potassium | K | Water regulation; enzyme activation; bud density | Brown/yellow leaf edges; weak stems; poor bud density; leaf scorch | Nutrient lockout (Ca, Mg); leaf tip burn |
¶ Secondary Macronutrients
| Nutrient | Symbol | Role | Notes |
|---|---|---|---|
| Calcium | Ca | Cell wall structure; root development | Often included in cal-mag supplements |
| Magnesium | Mg | Central atom in chlorophyll; enzyme activation | Deficiency shows as interveinal chlorosis on older leaves |
| Sulfur | S | Amino acid production; terpene synthesis | Deficiency: overall yellowing; often overlooked |
¶ Micronutrients
Required in trace amounts but essential for plant health:
| Micronutrient | Role | Deficiency Signs |
|---|---|---|
| Iron (Fe) | Chlorophyll synthesis; enzyme function | Interveinal chlorosis on new growth |
| Manganese (Mn) | Photosynthesis; nitrogen metabolism | Yellowing between veins; necrotic spots |
| Zinc (Zn) | Growth hormone production; enzyme function | Small, distorted new leaves; stunted growth |
| Boron (B) | Cell wall formation; calcium uptake | Brittle growing tips; hollow stems |
| Copper (Cu) | Enzyme activation; photosynthesis | Wilting; dark blue-green leaves |
| Molybdenum (Mo) | Nitrogen metabolism | Pale, cupped leaves; resembles nitrogen deficiency |
| Chlorine (Cl) | Osmotic regulation; photosynthesis | Rare deficiency; wilting |
¶ NPK Ratios by Growth Stage
Cannabis nutrient requirements shift dramatically through the life cycle.
| Stage | Ideal NPK Ratio | Explanation |
|---|---|---|
| Seedling | Very light or none | Seed contains enough nutrients for first 1-2 weeks; overfeeding kills seedlings |
| Early Vegetative | 3-1-2 (e.g., 9-3-6) | Higher nitrogen supports leaf and stem development |
| Late Vegetative | 3-1-2 (e.g., 9-3-6) | Maintain nitrogen-heavy feeding; increase overall strength |
| Transition (Pre-flower) | 2-2-3 (e.g., 6-6-9) | Begin reducing nitrogen; increase phosphorus and potassium |
| Early Flowering | 1-3-4 (e.g., 3-9-12) | Lower nitrogen; higher phosphorus and potassium for bud formation |
| Mid-Late Flowering | 0-3-4 (e.g., 0-9-12) | Minimal nitrogen; maximum P-K for bud density and resin production |
| Flush (Final 1-2 Weeks) | 0-0-0 (plain water) | Plain pH-balanced water only (see flushing debate below) |
¶ Organic vs. Synthetic Nutrients
| Factor | Organic Nutrients | Synthetic Nutrients |
|---|---|---|
| Composition | Derived from natural sources (bat guano, kelp, bone meal, fish emulsion) | Mineral salts manufactured chemically |
| Availability | Requires microbial breakdown; slower release | Immediately available to roots |
| Soil Health | Builds soil biology and structure over time | Does not contribute to soil life; can harm microbes at high concentrations |
| Flavor/Terpenes | Many growers report richer terpene profiles | Can produce excellent results; debated flavor difference |
| Precision | Less precise; nutrient release varies with temperature and biology | Precise and repeatable; exact EC/PPM control |
| pH Stability | More forgiving; soil buffers pH swings | Requires active pH management |
| Overfeed Risk | Lower risk of nutrient burn | Higher risk; burns easily |
| Hydroponic Use | Not suitable for most hydroponic systems (clogs lines) | Designed for hydroponics and soil |
| Cost | Often higher per feeding | Generally more economical |
| Best For | Soil growing; outdoor; organic-focused growers | Hydroponics; coco; precision-focused growers |
For a deeper look at how nutrient choices tie into sustainable growing practices, see Eco Friendly Cultivation.
¶ Popular Nutrient Lines
| Nutrient Line | Type | Best For | Price Range | Notes |
|---|---|---|---|---|
| Fox Farm Trio (Grow Big, Tiger Bloom, Big Bloom) | Organic/synthetic blend | Soil | $30-40 (set) | Widely available; proven results; gentle |
| General Hydroponics FloraSeries (FloraMicro, FloraGro, FloraBloom) | Synthetic | Hydroponics, coco, soil | $25-35 (set) | Industry standard; flexible; widely documented |
| Advanced Nutrients pH Perfect | Synthetic with pH buffer | Soil, coco | $40-60 (set) | pH Perfect technology; higher cost; extensive supplement line |
| Botanicare Pure Blend Pro | Synthetic + organic | Soil, coco | $30-45 (set) | Includes beneficial microbes |
| Canna Terra/Aqua | Synthetic | Soil (Terra), Hydro (Aqua) | $30-50 (set) | Strain-specific schedules available |
| BioBizz | 100% organic | Soil, outdoor | $35-55 (set) | Certified organic; living soil focus |
| Cult Solutions Complete | Synthetic all-in-one | All mediums | $40-60 (bottle) | Single bottle; extremely simple |
| Remo Nutrients | Synthetic | All mediums | $30-50 (set) | Clean feeding; popular in competitions |
| Masterblend (Tomato Formula + Cal-Mag + Epsom Salt) | Synthetic powder | Hydroponics, coco | $20-30 (5 lbs) | Most economical; requires mixing |
¶ Feeding Schedules
¶ Soil Feeding Schedule (Photoperiod, 4x4 Tent)
This is a general schedule using a 3-part nutrient system. Always start at 1/4 to 1/2 the manufacturer's recommended strength.
| Week | Stage | Nutrient Strength | EC Target (mS/cm) | Notes |
|---|---|---|---|---|
| 1 | Seedling | None or 1/8 strength | 0.2-0.4 | Plain water or very light nutrients |
| 2 | Seedling | 1/4 strength | 0.4-0.6 | First true leaves established |
| 3 | Early Veg | 1/2 strength | 0.6-0.8 | Increase gradually |
| 4 | Veg | 3/4 strength | 0.8-1.0 | Watch for deficiency or burn signs |
| 5 | Veg | Full strength | 1.0-1.2 | Peak vegetative feeding |
| 6 | Veg/Transition | Full strength | 1.0-1.2 | Last week of veg before flip |
| 7 | Early Flower (Stretch) | Transition formula | 1.0-1.4 | Switch to bloom nutrients |
| 8 | Flower Week 2 | Full bloom strength | 1.2-1.6 | Buds forming |
| 9 | Flower Week 3 | Full bloom strength | 1.4-1.8 | Peak feeding |
| 10 | Flower Week 4 | Full bloom strength | 1.4-1.8 | Buds fattening |
| 11 | Flower Week 5 | Full or 3/4 strength | 1.2-1.6 | Monitor for nutrient buildup |
| 12 | Flower Week 6 | 1/2 strength | 1.0-1.2 | Begin tapering |
| 13 | Flower Week 7 | 1/4 strength or flush | 0.4-0.6 | Final week or two: plain water |
| 14 | Flower Week 8 | Plain water (flush) | 0.2-0.4 | Harvest |
Note: Flowering duration varies by strain. 8-week flowers are common, but many strains require 9-12 weeks. Extend the flowering feeding schedule accordingly.
¶ Hydroponic Feeding Schedule
Hydroponic feeding uses the same nutrient progression but requires more frequent monitoring:
| Parameter | Frequency | Action |
|---|---|---|
| pH | Daily | Adjust to 5.5-6.5 |
| EC/PPM | Daily | Top off or adjust strength |
| Water Level | Daily | Top off with pH-balanced water |
| Full Reservoir Change | Every 7-10 days | Drain, clean, refill with fresh nutrients |
| Reservoir Temperature | Daily (minimum) | Maintain 65-68°F (18-20°C) |
¶ pH Management
pH determines nutrient availability. Even with perfect nutrient concentrations, incorrect pH locks out nutrients.
¶ pH Targets
| Growing Medium | Target pH Range | Optimal |
|---|---|---|
| Soil | 6.0-7.0 | 6.3-6.7 |
| Coco Coir | 5.5-6.5 | 5.8-6.0 |
| Hydroponics | 5.5-6.5 | 5.8-6.2 |
¶ pH Adjustment Routine
- Mix nutrients in water first (nutrients affect pH)
- Wait 15-30 minutes for nutrients to fully dissolve and react
- Measure pH with a calibrated pH pen or reliable drops
- Adjust with pH Up or pH Down, adding small amounts at a time
- Wait 15 minutes and re-measure to confirm stability
- Feed the plants
Important: Soil acts as a buffer and has a wider acceptable pH range. Hydroponic and coco systems have virtually no buffering capacity and require precise pH management.
¶ Understanding Nutrient Availability by pH
pH 5.0 |--N--|--P--|--K--|--Ca--|--Mg--|--Fe--|--Mn--|--Zn--|
pH 5.5 |---N--|--P--|--K--|--Ca--|--Mg--|--Fe--|--Mn--|--Zn-|
pH 6.0 |---N--|--P--|--K--|--Ca--|--Mg--|--Fe--|--Mn--|--Zn-|
pH 6.5 |--N---|--P---|--K--|--Ca--|--Mg--|--Fe--|--Mn--|--Zn|
pH 7.0 |-N----|-P----|--K--|--Ca--|--Mg--|-Fe---|-Mn---|-Zn|
Key: More dashes = better availability at that pH
Rule of thumb: In soil, pH 6.3-6.7 provides the broadest availability of all nutrients. In hydro/coco, pH 5.8-6.2 achieves the same.
¶ Nutrient Deficiency and Toxicity Identification
¶ Visual Identification Table
| Problem | Affected Leaves | Visual Signs | Cause | Treatment |
|---|---|---|---|---|
| Nitrogen Deficiency | Older (bottom) leaves | Uniform yellowing from bottom up; slow growth | Underfeeding; high demand during veg | Increase nitrogen; resume feeding |
| Nitrogen Toxicity | All leaves | Dark green; "clawing" (leaf tips curl down); brittle | Overfeeding | Reduce nitrogen; flush if severe |
| Phosphorus Deficiency | Older leaves | Dark green to purple/red; slow growth; poor flowering | Low P; cold temperatures; pH lockout | Increase P; verify pH; warm root zone |
| Phosphorus Toxicity | New growth | Rare; can lock out Fe, Zn, Ca | Extreme overfeeding | Flush; reduce P |
| Potassium Deficiency | Older leaves | Brown/yellow edges; weak stems; leaf scorch | Low K; high sodium competition | Increase K |
| Potassium Toxicity | Leaf tips | Tip burn; can lock out Ca, Mg | Overfeeding | Reduce K; flush |
| Calcium Deficiency | New growth | Brown spots; curling; weak new growth | Low Ca; low pH; low humidity | Add cal-mag; verify pH |
| Magnesium Deficiency | Older leaves | Interveinal chlorosis (yellow between green veins) | Low Mg; low pH; competitive ions | Add Epsom salt (1 tsp/gal) or cal-mag |
| Iron Deficiency | New growth | Bright yellow between veins on new leaves | High pH; excess P; low Fe | Lower pH; add chelated iron |
| Nutrient Burn | Leaf tips | Brown, crispy tips (most common on tips) | EC too high; overfeeding | Reduce EC; flush medium |
Important: Always check pH first before treating a deficiency. Most "deficiencies" are actually pH lockouts, not actual nutrient shortages.
¶ The Flushing Debate
Flushing -- feeding plain, pH-balanced water for 1-2 weeks before harvest -- is one of the most debated topics in cannabis cultivation.
¶ Arguments For Flushing
- Removes excess salts from the growing medium
- Forces the plant to use stored nutrients
- May improve smoothness and flavor of smoke
- Standard practice in commercial operations
¶ Arguments Against Flushing
- Limited peer-reviewed scientific evidence
- May starve the plant during critical final bud development
- Modern nutrient lines are clean and don't require flushing
- Some blind taste tests show no significant difference
¶ Middle Ground Recommendation
| Approach | Method |
|---|---|
| Conservative Flush | Reduce to 1/4 strength for final 7-10 days, then plain water for final 3-5 days |
| Taper Only | Gradually reduce feeding over final 2 weeks without complete flush |
| No Flush | Feed at reduced strength until harvest day |
The consensus among experienced growers leans toward at least a brief period of reduced feeding before harvest, even if a full flush is not performed.
¶ Cal-Mag Supplementation
Cal-Mag (calcium and magnesium) is one of the most common supplements in cannabis cultivation.
| Situation | Cal-Mag Needed? | Dosage |
|---|---|---|
| Reverse osmosis (RO) water | Yes; RO removes all minerals | 1-2 ml per gallon |
| Soft/tap water | Often; low mineral content | 1 ml per gallon |
| Hard water | Usually not; already contains Ca and Mg | Test water first |
| Coco coir | Yes; coco binds Ca and Mg | 1-2 ml per gallon from seedling |
| Soil (quality) | Sometimes; depends on soil composition | Start at 0.5 ml per gallon; monitor |
| Hydroponics | Depends on base nutrients | Check nutrient label; many include Cal-Mag |
¶ Troubleshooting: Feeding Problems
| Problem | Cause | Solution |
|---|---|---|
| pH keeps drifting down | Microbial activity; acidic nutrients | Use pH-stable nutrients; buffer with potassium silicate; check more frequently |
| pH keeps drifting up | Hard water; alkaline medium | Use RO water; add pH Down preemptively |
| EC rises between feedings (hydroponics) | Plant transpiring more water than nutrients | Top off with plain pH water to lower EC |
| EC drops between feedings (hydroponics) | Plant consuming nutrients faster than water | Top off with stronger nutrient solution |
| Persistent deficiency despite feeding | pH lockout; root disease; cold root zone | Check pH first; inspect roots; warm root zone to 65-70°F |
| White crust on soil surface | Salt buildup from overfeeding; hard water | Flush with 3x pot volume of pH water; reduce feeding strength |
| Yellowing lower leaves during flower | Natural senescence (plant redirecting nutrients) | Normal if only a few bottom leaves; monitor for progression |
¶ Related Pages
- Indoor Grow Guide -- Complete indoor grow with week-by-week nutrient schedules for soil and coco
- Outdoor Grow Guide -- Complete outdoor grow with organic soil amendments, compost tea, and living soil feeding
- Hydroponics -- Nutrient solution management for hydroponic systems
- Indoor Growing -- Feeding schedules for indoor soil grows
- Environmental Control -- How temperature and humidity affect nutrient uptake
- Pest & Disease Management -- Distinguishing nutrient issues from pest/disease damage
- Harvesting & Drying -- Flushing before harvest
- Strains -- Some strains are heavier feeders than others
See Also: /cultivation/indoor | /cultivation/indoor/hydroponics | /cultivation/indoor/environment | /cultivation/pests-diseases | /cultivation/harvest-dry