Companion planting is the practice of strategically placing different plant species near each other to create a mutually beneficial environment. This technique leverages natural interactions to improve plant health and increase yields. Peas, being members of the legume family, are especially well-suited for this method because of their unique relationship with soil microbes. The right plant neighbors can boost the pea plant’s growth while also benefiting significantly from the pea’s presence in the garden.
Companion Plants for Soil Enrichment and Physical Support
Peas host Rhizobium leguminosarum bacteria within specialized structures on their roots called nodules. This symbiotic relationship allows the pea plant to convert atmospheric nitrogen gas (\(\text{N}_{2}\)) into a plant-available form, ammonium (\(\text{NH}_{4}\)), a process known as nitrogen fixation. This natural enrichment benefits the pea, and after the plant dies back, the remaining nitrogen is released into the soil for subsequent crops.
Planting low-growing, non-competitive root vegetables alongside peas allows them to capitalize on this increased soil fertility. Carrots, radishes, and turnips have deep taproots that do not compete with the pea’s shallower root system for moisture and nutrients. These root crops also help to gently aerate the soil, which improves water penetration and oxygen supply to the pea roots.
Taller, sturdy plants can act as a natural trellis for vining pea varieties, saving the gardener the effort of installing artificial support structures. Pole corn and sunflowers serve as living stakes, providing vertical support for the pea tendrils to climb. This intercropping strategy also maximizes garden space by utilizing the vertical dimension.
Cool-weather crops, such as lettuce and spinach, make excellent ground cover when planted beneath trellised peas. Their broad leaves shade the soil, acting as a living mulch that keeps pea roots cool and helps to retain soil moisture. This microclimate regulation is particularly helpful in the spring when sudden temperature fluctuations can stress young pea plants.
Companion Plants for Pest and Disease Control
Aromatic plants can be strategically placed near pea rows to confuse or repel common insect pests that target the foliage and pods. Basil releases a scent that helps deter thrips, tiny insects that can damage pea flowers and stunt pod development. The strong aroma of herbs such as cilantro, mint, and oregano can mask the pea plant’s scent, making it difficult for pests like aphids and spider mites to locate their host.
Flowering plants can be used as attractors for beneficial insects that prey on pea pests. Nasturtiums act as a trap crop, as aphids and flea beetles prefer their leaves over pea foliage, drawing the pests away from the main crop. Sweet alyssum, a low-growing flower, attracts predatory insects like lacewings and parasitic wasps, which feed on or lay their eggs inside destructive pests.
Good air circulation is a simple yet effective measure against fungal diseases like powdery mildew, which thrives in humid, stagnant conditions. Companion plants that maintain a low profile and do not excessively crowd the pea plants promote better airflow around the leaves. Turnips are thought to have an added benefit as their root secretions may repel aphids, which are vectors for various pea viruses.
Plants to Strictly Avoid Planting Near Peas
Certain plants actively inhibit the growth of peas through chemical warfare or intense competition for limited resources. Members of the Allium family, including onions, garlic, and chives, possess allelopathic properties, meaning they release chemical compounds that can suppress the growth of nearby legumes. Large plantings of these pungent bulbs can significantly stunt the development and yield of pea plants.
Fennel is another strongly allelopathic plant that should be isolated from nearly all garden vegetables, including peas. It releases chemical substances from its roots that can negatively affect the growth and germination of surrounding plants. It is best to grow fennel in a dedicated area away from sensitive crops.
Heavy feeders, such as large members of the Brassica family (cabbage, broccoli, cauliflower) or potatoes, should also be kept separate from peas. These crops require large amounts of nutrients, especially nitrogen, and aggressively compete with the peas for available soil resources. While peas produce nitrogen, they require time to establish their symbiotic relationship and cannot keep up with the intense nutrient demand of these competitors.
Potatoes present a further risk because they can be hosts for certain diseases, such as blight, which can also affect peas. Planting them in close proximity increases the chance of disease transmission between the two crops. This combination of allelopathy, nutrient competition, and shared disease susceptibility makes careful plant placement necessary for a successful pea harvest.