Companion planting involves growing different crops together for mutual benefit, often leading to healthier plants and higher yields. Onions and lettuce are highly compatible partners due to their differing growth habits and protective qualities. This interplanting arrangement maximizes space and provides distinct biological advantages to both vegetables.
Mutual Benefits of Interplanting
The pungent, aromatic compounds released by onions serve as a natural defense mechanism for lettuce. The strong scent confuses and deters common pests, such as aphids and cutworms, ensuring a cleaner harvest.
The two vegetables avoid direct competition for resources beneath the soil surface. Lettuce has a shallow, fibrous root system, drawing nutrients from the topsoil. Conversely, onions focus on forming a bulb that pushes into deeper zones, accessing different nutrient and water reservoirs. This difference in root architecture minimizes the struggle for resources, allowing both crops to thrive.
As the season progresses, the taller, upright onion leaves provide partial shade for the low-growing lettuce, shielding it from intense midday heat. This cooling effect helps delay bolting, preventing the lettuce from prematurely sending up a flower stalk and becoming bitter. Furthermore, the broad leaves of the lettuce act as a living mulch, suppressing weeds and cooling the soil for the onions.
Proper Planning and Setup Techniques
Successful interplanting requires preparing a well-draining, fertile garden bed, as both are cool-season vegetables. Early spring is the ideal time for simultaneous planting. Using onion sets or transplants alongside lettuce seeds or transplants allows for the best timing.
A common configuration is planting lettuce in rows between the primary rows of onions. Onions should be spaced about 4 inches apart for proper bulb development. The lettuce fills the space between these rows, utilizing ground not covered by the upright onion leaves.
Another arrangement is planting lettuce around the perimeter of an onion block, using it as an edible border. Ensure the lettuce is not placed so close that it crowds the onion bulbs, which need sufficient space to swell. Amend the soil with compost, but avoid adding high-nitrogen fertilizer before planting onions, as this encourages foliage growth over bulb formation.
Navigating Varied Water and Harvest Schedules
Interplanting requires careful irrigation management, as water needs diverge later in the season. Lettuce needs consistent, shallow moisture to maintain crispness and prevent bitterness or bolting. Onions also require regular water, especially during bulb-forming stages, often needing up to 2 inches every four days during peak growth.
The conflict arises because mature onions require a gradual drying-out period for harvest and curing. Gardeners must manage this by watering the lettuce locally, using a watering can or drip irrigation focused only on the shallow-rooted lettuce plants. This allows the soil around the developing onion bulbs to dry out as needed.
Lettuce harvesting should begin early, using a “cut and come again” method or by harvesting entire heads. It is important to remove the lettuce completely before it grows large enough to shade or crowd the onion bulbs. Onions are harvested much later, typically when their green tops naturally fall over and yellow. Irrigation should cease entirely one to two weeks before this collapse, ensuring the bulbs are firm and ready for curing.