Lettuce Companion Plants

Claim. Deep-rooted carrots and shallow-rooted lettuce use different soil layers and similar light, so they interplant with little competition at normal spacing; a space-use principle from intercropping research rather than a crop-specific trial.

Mechanism. Complementary root depth and canopy size.

Conditions. Sow together in spring. Alternate rows 30 cm apart. Both plants must be present at the same time.

Applies when. Useful for filling a bed; both are cool-season crops.

Limitations. General principle; no carrot–lettuce trial found.

Evidence. Tier C: Indirect evidence: greenhouse or pot work, a related crop or species, or credible extension guidance with important uncertainty. (extension synthesis).

Sources. Brooker 2015; Cornell University 2024

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record carrot--lettuce--spatial_complement v1. Request a correction.

Claim. Corn casts deep shade to its north (in the northern hemisphere), which can keep summer lettuce cooler; in cool climates the same shade is a disadvantage.

Mechanism. Shade reduces heat stress and bolting.

Conditions. Plant lettuce once corn is knee-high. Lettuce along the shaded side of the corn block. Summer heat period.

Management. Extra water; corn is a heavy drinker.

Applies when. Hot summers.

Limitations. Not a benefit in cool or cloudy climates.

Evidence. Tier C: Indirect evidence: greenhouse or pot work, a related crop or species, or credible extension guidance with important uncertainty. (extension synthesis).

Sources. Cornell University 2024; Brooker 2015

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record corn--lettuce--shade_or_shelter v1. Request a correction.

Claim. Tall peas on netting cast light shade that can shelter late-spring lettuce as days warm; after the peas finish, the lettuce space is free for a summer crop.

Mechanism. Light shade and sequence of occupancy.

Conditions. Plant lettuce 3–4 weeks after peas. Lettuce on the shaded side of the pea row, 30 cm away. Both plants must be present at the same time.

Applies when. Spring beds.

Limitations. General practice; untested as a pair.

Evidence. Tier C: Indirect evidence: greenhouse or pot work, a related crop or species, or credible extension guidance with important uncertainty. (extension synthesis).

Sources. Cornell University 2024; Brooker 2015

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record peas--lettuce--shade_or_shelter v1. Request a correction.

Claim. Alyssum strips interplanted with organic lettuce supported hoverflies for aphid biocontrol; the agronomy showed one alyssum plant for roughly every 20–40 lettuce plants, within a few metres, was sufficient.

Mechanism. Nectar and pollen for adult hoverflies; larvae eat aphids.

Studied in. Organic romaine lettuce, Salinas Valley, California. (field)

Conditions. Transplant together. Alyssum plants every few metres within the lettuce bed. Alyssum flowering during lettuce growth.

Management. Replace lettuce plants with alyssum at a ratio of roughly 1:20 to 1:40.

Applies when. Reasonable to try in a home bed of lettuce; requires local hoverflies.

Limitations. Alyssum occupies lettuce space; the trade-off was small at low ratios.

Evidence. Tier B: One or more relevant controlled field studies or an authoritative synthesis tied to the crop, effect and arrangement. (field trial).

Sources. Brennan 2013; Hogg 2011

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record sweet-alyssum--lettuce--insectary_support v1. Request a correction.

Claim. Lettuce bolts and scorches in summer heat; the partial shade cast by tomatoes on their east or north side can extend the lettuce season. This is a spatial fit, not a biological companion effect.

Mechanism. Shade lowers leaf temperature and slows bolting in a heat-sensitive crop.

Studied in. Extension guidance on summer lettuce and general intercropping synthesis. (home garden)

Conditions. Sow or plant lettuce after tomatoes are 60 cm tall, in early summer. Lettuce 30–45 cm from tomato stems on the shaded side. Only meaningful in hot weather; in spring lettuce needs full sun.

Management. Keep lettuce watered; tomato roots compete for water.

Applies when. Summer only, in climates where lettuce struggles with heat.

Limitations. Too much shade produces weak lettuce; in cool climates it is a disadvantage.

Evidence. Tier C: Indirect evidence: greenhouse or pot work, a related crop or species, or credible extension guidance with important uncertainty. (extension synthesis).

Sources. Cornell University 2024; Brooker 2015

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record tomato--lettuce--shade_or_shelter v1. Request a correction.

Claim. We did not find a source that establishes a benefit or harm between onion and lettuce.

Mechanism. None documented.

Conditions. Planted together Both plants must be present at the same time.

Applies when. The planner evaluates spacing, light, water and timing normally.

Limitations. Commonly listed as compatible; no evidence found.

Evidence. Unknown: No source meeting the inclusion rules. (none).

Sources. University of Minnesota Extension 2023

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record onion--lettuce--other v1. Request a correction.

Claim. We did not find a source that establishes a benefit or harm between lettuce and radish.

Mechanism. None documented.

Conditions. Planted together Both plants must be present at the same time.

Applies when. The planner evaluates spacing, light, water and timing normally.

Limitations. Commonly interplanted for space; no benefit or harm documented.

Evidence. Unknown: No source meeting the inclusion rules. (none).

Sources. University of Minnesota Extension 2023

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record lettuce--radish--other v1. Request a correction.

Claim. We did not find a source that establishes a benefit or harm between lettuce and strawberry.

Mechanism. None documented.

Conditions. Planted together Both plants must be present at the same time.

Applies when. The planner evaluates spacing, light, water and timing normally.

Limitations. Both low and shallow-rooted; they compete for water but no relationship is documented.

Evidence. Unknown: No source meeting the inclusion rules. (none).

Sources. University of Minnesota Extension 2023

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record lettuce--strawberry--other v1. Request a correction.