Companion planting is a strategic approach to gardening that leverages the natural relationships between plants to create a more harmonious, healthy, and productive ecosystem. For the sweet pea (*Lathyrus odoratus*), selecting the right companions can enhance its growth, improve its fragrance, and protect it from common pests, all while maximizing the use of garden space.
From a plant's perspective, sweet peas are climbing annuals that require physical support to reach their full potential. They use tendrils to grasp onto structures and other plants. Tall, sturdy, non-invasive plants make excellent living trellises. Ideal companions for this purpose include ornamental grasses or sturdy-stemmed flowers like sunflowers. The sunflower provides a robust stalk for the sweet pea to climb, while the sweet pea, with its lighter leaf structure, does not heavily shade the sun-loving sunflower. This symbiotic relationship allows both plants to thrive without competing for vertical space.
Sweet peas can be susceptible to aphids and other sap-sucking insects. To combat this from a plant-centric view, we can employ companions that emit strong aromatic compounds through their foliage or flowers. These scents mask the attractive smell of the sweet peas or directly repel pests. Excellent aromatic companions include herbs like rosemary, lavender, and oregano. The pungent oils of these herbs create a protective barrier. Additionally, planting garlic or chives nearby can help deter aphids with their strong sulfurous compounds, providing a natural, chemical-free defense for the sweet peas.
Sweet peas are legumes, meaning they have a unique symbiotic relationship with nitrogen-fixing bacteria (*Rhizobia*) in their root nodules. These bacteria convert atmospheric nitrogen into a form the plant can use. From a soil nutrient perspective, this means sweet peas are relatively light feeders that can actually improve soil fertility for neighboring plants. They pair wonderfully with heavy feeders that benefit from the extra nitrogen. Leafy greens like lettuce and spinach or brassicas like kale are excellent choices. The sweet peas fix nitrogen, potentially making it available to the greens, which in turn have shallow root systems that do not compete aggressively with the sweet pea's roots.
While sweet peas are primarily grown for their beauty and fragrance, they do attract some pollinators. To create a garden that supports a wider ecosystem, plant companions that bloom in succession or attract beneficial insects. Low-growing, pollinator-friendly plants like alyssum or calendula planted at the base of sweet peas create a ground cover that helps retain soil moisture and suppress weeds. These companions attract hoverflies and predatory wasps, whose larvae are voracious consumers of aphids, offering a second layer of biological pest control. This partnership creates a more resilient and vibrant plant community.
