How long does hydroponic lettuce take?

28–35 days from seedling transplant to harvest, depending on variety and DLI. Add 14–21 days for germination + seedling stage. Total seed-to-harvest is typically 42–56 days for most home growers.

What pH and EC for lettuce?

pH 5.5–6.5 (ideal 6.0); EC 0.8–1.2 mS/cm (~560–840 PPM at the 700 scale). Higher EC produces sturdier leaves with stronger flavor; lower EC produces sweeter, more delicate leaves.

Why is my lettuce bolting?

Air temperature above 24 °C or photoperiod over 14 hours triggers bolting. Drop temps to 18–20 °C, shorten photoperiod to 12–14 h, and harvest immediately at first sign of flower stalk.

How much lettuce can I grow at home?

A 2×4 ft tent with proper LED grows 40–60 lettuce heads per year on continuous succession (4 new seedlings every 10 days). Enough for daily salads for 2 people indefinitely.

Best lettuce variety for beginners?

Buttercrunch butterhead. Most forgiving of temperature swings, fastest cycle, most flavorful for the least work. After one successful cycle, try romaine, looseleaf, or oak leaf for variety.

DOC №049SEC: PLANTSREV: 2026-05-19AUTHORED

How to Grow Lettuce Hydroponically

Lettuce is the easiest hydroponic crop — fast, forgiving, and high-yield. Complete guide to pH, EC, light, varieties, system selection, and continuous harvest.

BY ROOTLESS FARM

Quick answer

Hydroponic lettuce reaches harvest in 28–35 days from transplant at pH 6.0, EC 1.0, DLI 14, and water temperature 18–22 °C. The easiest hydroponic crop — forgiving of beginner mistakes, fast to harvest, and productive year-round indoors. Deep Water Culture, NFT, and the Kratky method all work; DWC is the most forgiving for first-time growers.

Conditions

Parameter	Value
pH	5.5–6.5 (6.0 ideal)
EC	0.8–1.2 mS/cm
Air temp	15–22 °C
Water temp	18–22 °C
Humidity	50–70%
DLI	14 mol/m²/day
Photoperiod	14 h
Spacing	20 cm
Days to harvest	28–35 (transplant)
Yield/plant	~200 g

Why lettuce is the universal first crop

Three traits make lettuce the standard "first hydroponic crop":

Forgiving. Tolerates wide pH (5.5–6.5), EC (0.8–1.4), and temperature (15–22 °C) ranges. Beginner mistakes rarely kill it.
Fast. 28–35 day cycles let you fail and recover within a single month.
Productive. Continuous succession yields 40–60 heads per year per square meter — enough for daily salads.

If you can't grow lettuce hydroponically, no other crop will work. If you can, every other leafy and herb crop becomes accessible.

Lettuce families and varieties

The lettuce category divides into four main groups, each with hydroponic implications:

Butterhead (Bibb, Boston)

Soft, cupped heads with tender leaves. Fastest to harvest, most forgiving. See butterhead lettuce for the deep dive.

Buttercrunch — classic, beginner-friendly.
Tom Thumb — miniature, dense raft-friendly.
Marvel of Four Seasons — red-tinged outer leaves.

Romaine (Cos)

Upright, sturdy leaves. Used for Caesar salads, wraps, and grilling. Slightly longer cycle (35–45 days).

Parris Island — classic, reliable.
Little Gem — miniature romaine, very compact.
Forellenschluss — red-speckled heirloom, striking.

Looseleaf

No head — continuous outer-leaf harvest. The highest-yield home lettuce. See looseleaf lettuce.

Oak Leaf (green or red) — most forgiving.
Lollo Rosso — frilly red, premium.
Black-Seeded Simpson — heritage productive.

Iceberg (Crisphead)

Dense, crisp heads. Hardest hydroponic lettuce — requires consistent cool temperatures. See iceberg lettuce.

Skip until you've succeeded with butterhead.

Recommended system

Deep Water Culture is the standard for home growers. A single 5-gallon DWC bucket produces 1–4 lettuce heads per cycle depending on plant size. RDWC (multi-bucket shared reservoir) scales easily to 8–16 plants.

Nutrient Film Technique excels at commercial scale — channels accommodate dense planting and continuous harvest. Industrial lettuce production runs almost entirely on NFT.

Kratky method is the simplest no-electricity option. A wide-mouth quart jar grows one lettuce head over 40–45 days. Ideal for classrooms, balconies, and off-grid setups. See DWC vs Kratky.

Ebb and flow with clay pebbles works well at moderate scale (16–30 plants per 2×4 tray). Forgiving and quiet.

Avoid drip + media for fragile heading lettuces — handling damages outer leaves at harvest. Bare-root systems (DWC, NFT, Kratky) keep heads intact.

Light and temperature management

Three rules for indoor lettuce:

Keep temperatures cool

Air 15–22 °C. Above 22 °C, plants bolt within days.
Water 18–22 °C. Cooler water = higher dissolved oxygen + slower bolting.
Night drop of 4–6 °C improves head density and flavor.

Insulate the reservoir, ventilate the tent, and consider a chiller for summer indoor production.

Get the photoperiod right

14 hours light. Longer photoperiods don't increase yield much and accelerate bolting.
Photoperiod creep from poorly-managed timers is a common cause of unexplained bolting. Verify schedule monthly.

Match DLI to crop variety

Butterhead, looseleaf: DLI 12–14 (PPFD 240–280 at 14h).
Romaine: DLI 14–17.
Iceberg: DLI 11–13 (lower keeps heads tight).

For PPFD details see PPFD and DLI explained and watts per plant.

Nutrient solution

Standard 3-part hydroponic nutrient (General Hydroponics Flora Trio, MasterBlend, House & Garden) at vegetative ratios. Target EC 1.0 mS/cm:

Lower (0.8) produces sweeter, more delicate leaves.
Higher (1.2) produces sturdier, more flavorful leaves with longer shelf life.
Above 1.4 risks tip burn in sensitive cultivars.

Cal-mag supplementation (2 mL/gallon) is required if using RO or distilled water. With moderately hard tap water, supplementation usually isn't needed.

For deep nutrient management see pH management and EC vs pH.

Succession planting for continuous harvest

The home grower's secret weapon: stagger plantings 10 days apart for unbroken supply.

Day 0: plant 4 seedlings.
Day 10: plant 4 more.
Day 20: plant 4 more.
Day 30: plant 4 more.
Day 40: first cycle ready to harvest. Plant 4 replacements.

By week 10, you harvest 4 heads per week indefinitely. A single 2×4 ft tent produces 200+ heads per year on this schedule.

Common problems

Tip burn (brown leaf edges): calcium deficiency at high EC, low airflow, or low humidity. Drop EC slightly, add cal-mag, increase tent fan. See calcium deficiency.
Pale, yellowing inner leaves: iron lockout above pH 6.5. Test pH; adjust down. See iron deficiency.
Limp, soft heads: water temperature too high (above 24 °C), low DO. Check water temp; verify air pump output.
Sudden bolting: heat + long photoperiod. Cool the room; shorten lights.
Slow growth despite correct conditions: water temperature too low (under 14 °C) or pH drift.
Slimy stem base: bacterial issue at high water temperature. Reduce temp; add hydrogen peroxide (1:200) flush.

Harvest

For head lettuce (butterhead, romaine, iceberg): cut at the base when the head feels full and slightly springy. Wash, spin-dry, refrigerate in a paper-towel-lined container for 7–10 days shelf life.

For looseleaf: take outer leaves continuously. The central crown keeps producing for 6–8 weeks. See looseleaf lettuce.

A mature butterhead weighs 130–180 g. Romaine reaches 200–300 g. Looseleaf cumulative production over 4–6 cuts: 150–200 g per plant.

Best system

Deep Water Culture for hobbyists; NFT or raft for commercial. Kratky for off-grid / no-pump setups. Mix and match based on what you're growing and how much attention you can give.

FAQ

5 entries

Q01How long does hydroponic lettuce take?: 28–35 days from seedling transplant to harvest, depending on variety and DLI. Add 14–21 days for germination + seedling stage. Total seed-to-harvest is typically 42–56 days for most home growers.
Q02What pH and EC for lettuce?: pH 5.5–6.5 (ideal 6.0); EC 0.8–1.2 mS/cm (~560–840 PPM at the 700 scale). Higher EC produces sturdier leaves with stronger flavor; lower EC produces sweeter, more delicate leaves.
Q03Why is my lettuce bolting?: Air temperature above 24 °C or photoperiod over 14 hours triggers bolting. Drop temps to 18–20 °C, shorten photoperiod to 12–14 h, and harvest immediately at first sign of flower stalk.
Q04How much lettuce can I grow at home?: A 2×4 ft tent with proper LED grows 40–60 lettuce heads per year on continuous succession (4 new seedlings every 10 days). Enough for daily salads for 2 people indefinitely.
Q05Best lettuce variety for beginners?: Buttercrunch butterhead. Most forgiving of temperature swings, fastest cycle, most flavorful for the least work. After one successful cycle, try romaine, looseleaf, or oak leaf for variety.