The sweet pea, Lathyrus odoratus, is an annual flower known for its intensely fragrant blooms and charming appearance. Gardeners frequently seek this plant to add vertical interest and a wide spectrum of color to their landscapes. The species has a natural vining habit, using slender tendrils to climb available structures as it grows. The final height can vary substantially depending on the specific variety.
Defining Sweet Pea Varieties and Their Heights
The final height of a sweet pea plant is genetically determined and falls into two main categories: climbing or dwarf varieties. Climbing types are the classic sweet peas, typically reaching impressive heights of six to ten feet when given proper support. These vigorous vines are favored for creating fragrant screens, covering arches, or producing long-stemmed flowers for cutting. The ‘Spencer’ varieties, for example, are prized for their large, ruffled blooms and commonly achieve heights between six and eight feet.
In contrast, the bush or dwarf types of sweet peas offer a compact growth habit, making them suitable for smaller spaces and containers. These varieties generally grow only between one and three feet tall, and some ultra-dwarf selections may reach as little as eight inches. Dwarf sweet peas, like the ‘Little Sweetheart’ series, are bred to be self-supporting, eliminating the need for a trellis. Semi-dwarf types represent an intermediate range, growing to about four feet.
Environmental Factors That Influence Growth
Sweet peas require specific environmental inputs to reach their maximum size. Full sunlight is necessary for vigorous stem growth, though afternoon shade can prevent the plant from prematurely wilting in regions with intense summer heat. The plant prefers a cool, mild climate and will often stall or stop flowering entirely when daytime temperatures consistently climb above 80 degrees Fahrenheit. This temperature sensitivity limits the plant’s overall seasonal growth.
Soil quality plays a significant role in supporting a tall, healthy vine structure. Sweet peas perform best in rich, well-draining soil that has been generously amended with organic matter, such as compost or well-rotted manure. While adequate nutrition is required for height, excessive nitrogen should be avoided. Too much nitrogen promotes lush foliage growth at the expense of flower production. Consistent, deep watering is also required to support the rapid growth of a tall vine, especially during dry periods.
Maximizing Vertical Growth
For climbing varieties to achieve their maximum height, physical intervention and support are non-negotiable. Sweet peas are natural climbers that use tendrils to grasp available surfaces, but they cannot support a six-to-ten-foot structure without a dedicated system. Installing a trellis, netting, wire fence, or bamboo canes at the time of planting provides the necessary structure for the tendrils to twine around. Without this support, the stems will collapse into a tangled mound, limiting their upward reach.
Pinching for Robust Growth
A horticultural technique called “pinching” is employed to encourage stronger, taller growth. When the young seedling reaches about six inches in height, the main growing tip is removed. This process forces the plant to redirect growth hormones into the side shoots. This action results in a plant with multiple stems emerging from the base, leading to a bushier, more robust plant that can better support its eventual height. As the vine grows, errant stems may need to be manually tied to the support structure to ensure continuous vertical movement toward the sun.