Hydroponic Lettuce: Complete Indoor Growing Guide

Why grow Lettuce indoors?

The quintessential hydroponic crop: fast-growing, forgiving, and productive in almost any indoor setup. Loose-leaf varieties deliver harvests in under four weeks.

Hydroponics removes the variables that make Lettuce frustrating outdoors: inconsistent moisture, compacted soil, and seasonal weather. With precise pH, EC, and light control you can expect reliable, repeatable results year-round in an apartment or any indoor space.

Data point worth knowing: At solution temperatures above 24 °C, lettuce tip burn (calcium deficiency caused by low transpiration, not low Ca) appears even in a well-balanced nutrient solution - dropping reservoir temperature to 18–20 °C resolves it without adjusting nutrients.

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Ideal conditions

| Parameter | Target | |-----------|--------| | Light | 12–14 h/day | | pH range | 5.5–6.5 (optimal: 6.0) | | EC (nutrient strength) | 0.8–1.6 mS/cm | | Water temperature | 18–22 °C | | Days to first harvest | 25–35 |

Key nutrients to monitor:

• Calcium: critical for preventing tip burn
• Nitrogen: drives leaf mass; use NH4:NO3 ratio ≤ 1:5
• Potassium: supports water regulation in leaves

Keep pH within the stated range; nutrients become unavailable (locked out) when pH drifts even one unit outside the window. Check with a calibrated pH meter - pH pen strips are not accurate enough for hydroponics.

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Step-by-step growing

1. Germinate seeds in rockwool cubes or rapid rooter plugs; keep moist at 20–22 °C for 3–5 days.
2. Transplant seedlings to net pots in your DWC, NFT, or Kratky system when roots reach 2–3 cm.
3. Set nutrient solution to EC 0.8–1.2 and pH 5.8–6.2; increase EC to 1.4–1.6 in the final week.
4. Run lights 12–14 h/day; blue-spectrum LEDs (5000–6500 K) keep leaves compact.
5. Harvest outer leaves when they reach 10–15 cm, leaving the central growing tip intact.

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Common problems

| Problem | Fix | |---------|-----| | Tip burn (brown leaf edges) | Lower reservoir temperature to 18–20 °C and ensure good air circulation; do not add more calcium. | | Leggy, pale growth | Increase daily light integral - add hours or move lights 5 cm closer. | | Slimy roots | Light is leaking into your reservoir. Cover all openings and add beneficial bacteria (Bacillus subtilis). |

When diagnosing issues, always check pH and EC first - most problems in hydroponics trace back to one of those two variables before any nutrient deficiency or pest is the true cause.

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Harvest & nutrition

Cut-and-come-again harvesting extends the productive life of each plant to 8–12 weeks. Lettuce is 95% water by weight; consume within 3–5 days of harvest for peak crunch.

Expected yield: Continuous cut-and-come-again; 60–90 g per plant per week

Regular harvesting is not just practical - it usually encourages the plant to produce more. Harvesting too infrequently often leads to bolting (in leafy crops) or quality decline.

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This guide is reviewed against published horticultural research. It is not a substitute for advice from your local cooperative extension or certified horticulturalist. Nutritional information is general and not a health claim.