Planting lettuce and collards together successfully is possible using a gardening technique known as intercropping. Lettuce is a quick-maturing, shallow-rooted, cool-season crop. Collards, a member of the brassica family, are slower-growing, taller, and require more space to reach their full potential. This difference in growth habit allows for strategic planting where one crop can benefit the other by sharing space and resources.
Comparing Environmental and Nutritional Needs
Both lettuce and collards thrive in cooler weather and prefer rich, well-draining soil with consistent moisture. This shared preference simplifies bed preparation and basic watering routines. However, the plants diverge significantly in their light requirements as the season progresses. Collards require full sun exposure to develop strong, large leaves, while lettuce benefits greatly from shade, particularly as temperatures climb toward the end of spring.
Collards are heavy feeders, demanding substantial nitrogen to fuel their large, leafy growth, and they also require a neutral to slightly acidic soil pH of 5.5 to 6.8. Lettuce, by contrast, is far less demanding on soil fertility and requires less nitrogen to reach maturity. If both crops are planted simultaneously in the same space, the aggressively feeding collards can easily outcompete the lettuce for available nutrients. This difference must be accounted for to prevent the lettuce from becoming stunted or yellowed due to nitrogen deficiency.
Both plants are cool-season leafy greens, but their root systems occupy different soil zones. Lettuce has a shallow root system, drawing moisture and nutrients from the top few inches of soil. Collards develop a deeper, more extensive root network, accessing resources the lettuce roots cannot reach. This difference in rooting depth reduces direct competition for the same pool of resources beneath the soil surface.
Strategic Planting for Mutual Benefit
Successful intercropping relies on using the taller, slower-growing collards to shelter the lettuce from excessive heat and sun. Collard plants should be set out slightly earlier than the lettuce, allowing them a head start to establish upward growth. The lettuce is then planted in the spaces between the collards, positioned to eventually be cast in the shade of the maturing collard canopy.
This arrangement maximizes garden space utilization through a vertical layering approach. The fast-maturing, shallow-rooted lettuce can be harvested quickly (within 30 to 60 days), filling the ground area while the collards are still young. This strategy ensures a high yield per square foot, as the lettuce is removed before the collards expand their large leaves and require the full space.
To manage the difference in nitrogen needs, collards should be side-dressed with a nitrogen-rich fertilizer a few weeks after planting. This method applies the concentrated nutrient boost directly to the heavy feeders without over-fertilizing the nearby lettuce, which could lead to excessively soft growth. Applying fertilizer strategically ensures both plants receive the appropriate level of nutrition without intense competition.
Collards, being brassicas, are highly attractive to pests like the cabbage worm and cabbage looper. While lettuce may share some common pests, like aphids, the collards can act as a sacrificial crop, drawing the attention of brassica-specific pests away from other plants. Gardeners can then apply targeted pest control measures, such as Bacillus thuringiensis (Bt), directly to the collards to protect the entire planting area without treating the lettuce unnecessarily.
Managing Maintenance and Harvest
As collard plants grow, their large leaves increase their water requirement significantly. This growth also casts a denser shade over the lettuce, which slows water evaporation from the soil surface. Gardeners must carefully monitor moisture levels around the shaded lettuce, ensuring the soil remains consistently moist without becoming waterlogged, which could lead to fungal diseases.
The intercropped space must be managed as a succession planting, timing the removal of the first crop to benefit the second. As the lettuce reaches harvestable size, it should be removed promptly to prevent bolting (sending up a seed stalk and turning bitter). Removing the lettuce frees up the nutrients and space the collard plants need for continued expansion and maturation.
Harvesting techniques differ for each plant and must be executed carefully to avoid damaging the neighboring crop. Loose-leaf lettuce is best harvested using the cut-and-come-again method, where only the outer leaves are snipped, leaving the central growing point intact for future harvests. Collard leaves are harvested similarly, selecting the lower, outer leaves when they are about 8 to 10 inches long, allowing the plant to continue growing upward and producing new foliage.