Optimal Growing Conditions by Crop & Growth Stage
The full environmental target set for 10 indoor crops, stage by stage: day and night temperature, relative humidity, VPD, CO₂, nutrient EC and pH, and DLI. Programmable as controller setpoints, and cross-referenced against the VPD and DLI calculators so all three read as one system.
What Determines a Crop’s Optimal Growing Conditions
A crop’s optimal growing conditions are the target values for every parameter a grower actually controls: air temperature day and night, relative humidity, CO₂ concentration, VPD, nutrient EC, pH, DLI, and dissolved oxygen. None of them stands alone. Temperature and humidity together set VPD, which governs transpiration and therefore how fast nutrients move into the plant; light sets the DLI a crop can convert, but only if CO₂ and transpiration can keep up with it; EC sets feed strength, but pH decides which of those nutrients the root can actually take up. Every optimum shifts by growth stage — a seedling and a fruiting plant of the same species want measurably different environments — which is why a single “ideal temperature” figure for a crop is close to useless on a commercial farm. The day/night differential (DIF) matters on its own: a positive DIF promotes stem elongation, and a 6–8°F night drop keeps lettuce compact.
How to Use This Calculator
- 1 Find your crop in the reference table below, or select it in the calculator above to see every stage and parameter at once.
- 2 Choose a growth stage. Each stage has different optimal ranges reflecting the plant’s changing needs from propagation through harvest.
- 3 Review the low, target, and high thresholds for each parameter. Program the target as your controller setpoint and the low/high as alarm bounds.
- 4 Read the grower notes for stage-specific tips on temperature DIF, CO₂ supplementation timing, and common pitfalls.
Optimal Growing Conditions by Crop
Targets at each crop’s main production stage. Temperatures are target values in °F; VPD, EC and pH are the working ranges; DLI is the daily target in mol/m²/day. Every crop row has its own anchor and can be linked directly.
| Crop | Stage | Day / Night (°F) | RH (%) | VPD (kPa) | CO₂ (ppm) | EC (mS/cm) | pH | DLI |
|---|---|---|---|---|---|---|---|---|
| Butterhead | Grow-out | 72 / 64 | 65 | 0.8–1.2 | 1,200 | 0.8–1.5 | 5.6–6.2 | 16 |
| Romaine | Grow-out | 72 / 64 | 65 | 0.8–1.2 | 1,200 | 1.0–1.8 | 5.8–6.2 | 17 |
| Basil | Vegetative | 80 / 70 | 60 | 0.9–1.3 | 1,400 | 1.0–1.8 | 5.5–6.2 | 20 |
| Arugula | Grow-out | 65 / 60 | 65 | 0.8–1.1 | 1,000 | 0.8–1.5 | 5.8–6.5 | 15 |
| Kale | Grow-out | 70 / 60 | 65 | 0.8–1.2 | 1,200 | 1.2–2.0 | 5.8–6.5 | 17 |
| Microgreens | Greening | 70 / 65 | 65 | 0.5–0.9 | 1,000 | 0.0–1.0 | 5.5–6.5 | 14 |
| Strawberry | Fruiting | 72 / 62 | 60 | 1.0–1.5 | 1,200 | 1.4–2.2 | 5.5–6.2 | 24 |
| Tomato | Vegetative | 78 / 65 | 65 | 0.9–1.3 | 1,400 | 2.0–3.0 | 5.5–6.2 | 25 |
| Cucumber | Vegetative | 80 / 72 | 70 | 0.8–1.2 | 1,400 | 1.5–2.5 | 5.5–6.0 | 25 |
| Pepper | Vegetative | 80 / 68 | 65 | 0.9–1.3 | 1,400 | 1.8–2.8 | 5.5–6.2 | 22 |
Values are compiled from Cornell CEA, Sonneveld formulations, University of Arizona CEAC, and published indoor farming literature, and match the calculator above parameter for parameter. Pepper is the one crop here with no row on the DLI reference — use the 18–26 mol/m²/day band from the stage table below.
Every Growth Stage, Every Crop
The same parameters across all 29 crop-and-stage combinations. Ranges are low to high; program the midpoint as your setpoint and the bounds as alarms. Temperatures are target day / night in °F, DLI in mol/m²/day.
| Crop | Stage | Day / Night (°F) | RH (%) | VPD (kPa) | CO₂ (ppm) | EC (mS/cm) | pH | DLI |
|---|---|---|---|---|---|---|---|---|
| Butterhead | Propagation | 72 / 65 | 65–80 | 0.4–0.8 | 1,000 | 0.5–1.0 | 5.6–6.2 | 8–12 |
| Butterhead | Grow-out | 72 / 64 | 55–70 | 0.8–1.2 | 1,200 | 0.8–1.5 | 5.6–6.2 | 14–17 |
| Butterhead | Pre-Harvest | 68 / 62 | 50–65 | 1.0–1.3 | 1,000 | 0.6–1.2 | 5.6–6.2 | 14–17 |
| Romaine | Propagation | 72 / 65 | 65–80 | 0.4–0.8 | 1,000 | 0.5–1.0 | 5.8–6.2 | 8–12 |
| Romaine | Grow-out | 72 / 64 | 55–70 | 0.8–1.2 | 1,200 | 1.0–1.8 | 5.8–6.2 | 15–18 |
| Romaine | Pre-Harvest | 68 / 62 | 50–65 | 1.0–1.3 | 1,000 | 0.8–1.5 | 5.8–6.2 | 15–18 |
| Basil | Propagation | 76 / 70 | 65–80 | 0.4–0.8 | 1,000 | 0.5–1.0 | 5.5–6.2 | 8–12 |
| Basil | Vegetative | 80 / 70 | 50–70 | 0.9–1.3 | 1,400 | 1.0–1.8 | 5.5–6.2 | 18–22 |
| Basil | Harvest | 80 / 70 | 50–65 | 1.0–1.4 | 1,200 | 1.0–1.6 | 5.5–6.2 | 18–22 |
| Arugula | Propagation | 68 / 62 | 65–80 | 0.4–0.8 | 1,000 | 0.5–1.0 | 5.8–6.5 | 8–12 |
| Arugula | Grow-out | 65 / 60 | 55–70 | 0.8–1.1 | 1,000 | 0.8–1.5 | 5.8–6.5 | 12–18 |
| Kale | Propagation | 70 / 62 | 65–80 | 0.4–0.8 | 1,000 | 0.5–1.0 | 5.8–6.5 | 8–12 |
| Kale | Grow-out | 70 / 60 | 55–70 | 0.8–1.2 | 1,200 | 1.2–2.0 | 5.8–6.5 | 14–20 |
| Microgreens | Germination | 72 / 68 | 75–90 | 0.2–0.5 | 600 | 0.0–0.5 | 5.5–6.5 | 0–2 |
| Microgreens | Greening | 70 / 65 | 55–75 | 0.5–0.9 | 1,000 | 0.0–1.0 | 5.5–6.5 | 10–18 |
| Strawberry | Establishment | 72 / 64 | 60–75 | 0.5–0.9 | 1,000 | 0.8–1.4 | 5.5–6.2 | 14–18 |
| Strawberry | Flowering | 72 / 62 | 55–70 | 0.9–1.3 | 1,200 | 1.2–2.0 | 5.5–6.2 | 20–24 |
| Strawberry | Fruiting | 72 / 62 | 55–70 | 1.0–1.5 | 1,200 | 1.4–2.2 | 5.5–6.2 | 22–26 |
| Tomato | Transplant | 75 / 65 | 60–75 | 0.4–0.8 | 1,000 | 1.0–2.0 | 5.5–6.2 | 15–18 |
| Tomato | Vegetative | 78 / 65 | 55–70 | 0.9–1.3 | 1,400 | 2.0–3.0 | 5.5–6.2 | 22–28 |
| Tomato | Flowering | 76 / 64 | 55–70 | 1.0–1.5 | 1,200 | 2.5–3.5 | 5.5–6.2 | 22–28 |
| Tomato | Fruiting | 76 / 65 | 55–70 | 1.2–1.6 | 1,200 | 2.5–4.5 | 5.5–6.2 | 25–30 |
| Cucumber | Transplant | 78 / 70 | 65–80 | 0.4–0.8 | 1,000 | 1.0–2.0 | 5.5–6.0 | 15–20 |
| Cucumber | Vegetative | 80 / 72 | 60–80 | 0.8–1.2 | 1,400 | 1.5–2.5 | 5.5–6.0 | 20–30 |
| Cucumber | Fruiting | 80 / 72 | 60–75 | 1.0–1.5 | 1,200 | 2.0–3.0 | 5.5–6.0 | 22–30 |
| Pepper | Transplant | 78 / 68 | 60–75 | 0.4–0.8 | 1,000 | 1.0–2.0 | 5.5–6.2 | 15–20 |
| Pepper | Vegetative | 80 / 68 | 55–70 | 0.9–1.3 | 1,400 | 1.8–2.8 | 5.5–6.2 | 18–26 |
| Pepper | Flowering | 76 / 65 | 55–70 | 1.0–1.5 | 1,200 | 2.0–3.0 | 5.5–6.2 | 20–28 |
| Pepper | Fruiting | 76 / 65 | 55–70 | 1.2–1.6 | 1,200 | 2.5–3.5 | 5.5–6.2 | 22–30 |
Microgreens germinate in blackout, which is why their germination DLI is 0–2 mol/m²/day and their humidity target is the highest on this page. Fruiting crops climb in EC as they set fruit; leafy greens drop theirs before harvest to cut bitterness and tip burn.
Frequently Asked Questions
What are the optimal growing conditions for lettuce?
Butterhead and romaine both run 72°F day / 64°F night at 65% RH during grow-out, which puts VPD at 0.8–1.2 kPa. Target 16 mol/m²/day DLI for butterhead and 17 for romaine, CO₂ at 1,200 ppm, and pH 5.6–6.2. EC differs: butterhead 0.8–1.5 mS/cm, romaine 1.0–1.8 for dense heart formation. Drop temperature and EC in the 48 hours before harvest to reduce bitterness and tip burn.
What are the optimal growing conditions for basil?
Basil is tropical and wants it warm: 80°F day / 70°F night at 60% RH, VPD 0.9–1.3 kPa, DLI 18–22 mol/m²/day, CO₂ up to 1,400 ppm, EC 1.0–1.8 mS/cm, pH 5.5–6.2. The hard floor is the night temperature — below 65°F basil takes chilling injury that shows as dark spots within hours, and germination stalls entirely. High DLI plus CO₂ is what drives essential oil content.
What are the optimal growing conditions for tomatoes?
In vegetative growth, 78°F day / 65°F night at 65% RH, VPD 0.9–1.3 kPa, DLI 22–28 mol/m²/day, CO₂ 1,400 ppm, EC 2.0–3.0 mS/cm, pH 5.5–6.2. Through flowering and fruiting the temperature comes down slightly to 76°F day, VPD climbs to 1.2–1.6 kPa, and EC climbs hard — up to 2.5–4.5 mS/cm at fruiting, the highest feed strength on this page.
Why do optimal growing conditions change by growth stage?
Because the plant is doing different work. A seedling has almost no root surface and little leaf area, so it wants low EC, low VPD and modest light — strong feed burns young roots and high VPD dries tissue that cannot yet replace the water. A fruiting plant is moving large volumes of water and minerals into developing fruit, so it wants high EC, higher VPD to keep transpiration pulling, and the highest DLI it can convert. Programming one setpoint for a whole crop cycle means being wrong at both ends of it.
What is DIF in indoor farming?
DIF is the difference between day and night temperature. A positive DIF (warmer days, cooler nights) promotes stem elongation and is standard for most crops. A 6–8°F drop at night encourages compact growth in lettuce and triggers developmental signals. Basil requires a minimum night temperature of 65°F to avoid chilling injury.
When should I supplement CO₂?
CO₂ supplementation is most effective when light levels are high enough for plants to use the extra carbon. Supplement only during the photoperiod (lights-on), and only when VPD and temperature are in their optimal ranges. Most leafy greens benefit from 1,000–1,500 ppm; ambient air is ~420 ppm.
How does water temperature affect root health?
Nutrient solution temperature affects dissolved oxygen levels and root disease risk. Most crops prefer 64–72°F water temperature. Above 75°F, dissolved oxygen drops and pythium risk increases significantly. Below 60°F, nutrient uptake slows. Chilling systems are essential in warm climates.
What dissolved oxygen level do roots need?
Healthy hydroponic roots need at least 5 ppm dissolved oxygen (DO), with 8–10 ppm being optimal. DWC and NFT systems should target 6+ ppm. Aeroponics inherently provides high DO through air exposure. Low DO leads to anaerobic conditions, root browning, and pythium infection.
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