The sweet pea, Lathyrus odoratus, is an annual flower cherished for its intense fragrance and wide range of colors. Successfully growing these cold-hardy annuals begins with proper planning and preparation, as their best performance comes from an early start in the season. Establishing sweet peas correctly from the seed stage is the most effective way to ensure a robust, productive, and beautifully flowering garden display. These vines are well-suited to climbing, creating vertical accents in the garden landscape.
Preparing Sweet Pea Seeds for Sowing
Sweet pea seeds possess a naturally hard outer shell, or seed coat, which is designed to prevent premature germination. This tough coating can significantly delay the seeds from taking up the necessary moisture to sprout, leading to uneven or slow germination. To overcome this natural defense, gardeners employ two simple techniques: scarification and soaking.
Scarification involves physically weakening the seed coat to allow water penetration. This can be done by gently nicking the seed with a sharp knife or by rubbing it with sandpaper or a file. It is important to avoid damaging the small “eye,” or hilum, where the seed was attached to the pod.
Following scarification, the seeds should be soaked in room-temperature water for 12 to 24 hours. Soaking the scarified seeds allows them to imbibe water, visibly swelling them and initiating the metabolic processes required for growth. Seeds that swell demonstrate viability and are ready to be planted immediately afterward. Soaking for longer than 24 hours is not recommended, as it can cause the seeds to rot.
Selecting the Right Location and Timing
Sweet peas thrive in conditions that provide ample sunlight while keeping their roots cool and moist. They require a minimum of six hours of direct sun daily to produce the most abundant flowers. The ideal soil should be well-draining, deep, and rich in organic matter, with a slightly alkaline pH, generally between 6.0 and 7.5.
These plants are cold-tolerant and should be planted early in the season, as they prefer to establish themselves in cool temperatures. In most climates, seeds are best sown four to six weeks before the last expected hard frost date, as soon as the soil is workable.
This early planting allows the root system to develop fully before the heat of summer arrives, which can cause the plants to cease flowering. Gardeners in mild-winter regions may choose to plant seeds in the late fall or early winter for an early spring bloom.
Step-by-Step Planting Guide
Sweet pea seeds can be successfully started either indoors in deep containers or directly sown into the garden bed. Starting indoors is often recommended because sweet peas do not tolerate root disturbance well. They should be planted in biodegradable pots that can be placed directly into the ground. Use a deep container or prepare a deep trench in the garden to accommodate their long taproots.
Plant the prepared seeds about one-half to one inch deep into the soil. When planting multiple seeds, space them approximately four to six inches apart to ensure adequate air circulation and room for growth. If direct sowing, consider planting two to three seeds per spot and thinning them later.
After placing the seeds, gently cover them with soil and lightly firm the surface with your hand. The seeds require darkness for germination, so ensure they are fully covered. Water the area thoroughly right after planting to settle the soil and maintain consistent moisture until the seedlings emerge, which typically takes between one and two weeks.
Initial Care and Support Structures
Once the seeds have been planted and covered, the initial care focuses on consistent moisture and early support. The soil must be kept evenly moist but never waterlogged, which can lead to fungal diseases and root rot. Once the seedlings have developed two to three sets of true leaves and reached a height of about four to six inches, they should be thinned out.
Thinning involves removing the weaker seedlings to leave the strongest plant at each desired spacing interval. This promotes better air circulation and prevents overcrowding. At this stage, it is also beneficial to pinch out the central growing tip of the seedling, encouraging the plant to branch out at the base for a bushier habit and more flower production.
As vining plants, sweet peas require vertical support structures to climb, such as a trellis, netting, or sturdy stakes. These supports must be installed at the time of planting or shortly thereafter. Their delicate roots are easily damaged by later installation, as the vines will begin seeking purchase early on.