Sweet peas (Lathyrus odoratus) are popular annuals cherished for their highly fragrant, colorful blooms. The majority of cultivated varieties are natural climbers, a characteristic that requires vertical growth for the plant’s overall health and the production of abundant flower stems. Allowing these vines to ascend keeps the foliage aerated, which helps prevent common fungal diseases and maximizes sun exposure for flowering.
The Climbing Mechanism: Tendrils
Sweet peas achieve their ascent using specialized, delicate appendages called tendrils. These are thin, thread-like structures that emerge directly from the plant’s stems and leaf axils, differing significantly from plants that climb by twining their entire stem.
Once a tendril touches a suitable object, a rapid, internal process called thigmotropism is triggered. This response causes the side of the tendril touching the support to grow slower than the opposing side, resulting in a tight spiral wrap around the structure. The tendril quickly hardens after securing its grip, providing a strong anchor that pulls the main stem upward toward the light.
If the developing tendrils cannot find purchase on a narrow support, the plant’s weight will cause the stems to sprawl across the ground. A sprawling habit leaves the stems vulnerable to pests and diseases from soil contact and severely limits the plant’s ability to produce long, straight flower stalks.
Providing Optimal Support Structures
To ensure successful vertical growth, a support structure must be installed immediately after planting or sowing seeds, giving the young tendrils an immediate target. The ideal support should be rough or narrow enough for the fine tendrils to wrap around, as they struggle to grip smooth, wide surfaces like solid walls. Selecting a structure that can accommodate the plant’s mature height, typically between 6 to 8 feet, is necessary to prevent the vines from collapsing over the top.
Netting and Mesh
One of the most effective solutions is using vertical netting or mesh, which provides numerous small attachment points perfectly suited for the tendrils. Horticultural netting made of natural materials like jute or thin plastic mesh with a grid size of approximately 2 to 4 inches works exceptionally well. These nets should be stretched taut between two fixed points to prevent sagging, which could cause the vines to bunch up and restrict air flow.
Trellises and Obelisks
Alternatively, metal or wooden trellises offer rigid support, provided they have slim horizontal or vertical members for the small tendrils to secure themselves. A classic choice is constructing a teepee or obelisk using three or more bamboo canes or sturdy wooden poles driven into the planting bed. These conical structures allow the plants to grow in a visually appealing shape while maximizing air circulation around the dense foliage, which is beneficial in humid conditions.
Anchoring and Training
Gardeners should ensure the support is firmly anchored in the ground, as the mature, moisture-laden sweet pea vines can exert considerable force. The plant’s sheer weight and continuous pressure from wind require a strong foundation to prevent the entire structure from toppling over. Early training by gently guiding the first few tendrils onto the support ensures the plant establishes its climbing habit successfully from the start.
Understanding Bush and Dwarf Sweet Peas
While the majority of cultivated sweet peas are vigorous climbers, not all varieties exhibit this tall, vining habit. Horticultural breeding has produced specific bush and dwarf cultivars, such as the ‘Bijou’ or ‘Cupid’ series, which possess a more compact growth pattern. These varieties typically remain short, reaching heights of only 12 to 24 inches, and are considered self-supporting. These non-climbing types are suited for situations where vertical support is impractical, such as in containers, hanging baskets, or the front of a garden border. They do not require any trellising for healthy development.