Sweet peas (Lathyrus odoratus) are annual flowers valued for their intense fragrance. The journey from seed to bloom requires patience and a cool climate. The overall timeline to flowering varies based on the planting method, local environment, and care. Understanding the stages of development provides clear expectations for when to anticipate the first display of color and scent.
The Initial Stages: From Seed Sowing to Sprout
The first stage begins with preparing and sowing the seed. Sweet pea seeds have a hard outer coat, so many growers scarify them by lightly nicking the surface or soaking them in water for up to 24 hours. This preparation accelerates germination, allowing sprouts to appear within seven to ten days, compared to the ten to twenty-one days required for untreated seeds.
Optimal germination occurs when the planting medium is cool, ideally between 50 and 65 degrees Fahrenheit. Sowing typically happens in late autumn in mild winter areas or in early spring for colder climates, about ten to twelve weeks before the last expected frost date. Once the seedling emerges, move it to a cool, bright location to develop a strong root system. Before transplanting outdoors, “hardening off” gradually acclimates the young plants to outdoor conditions, preparing them for vigorous growth.
The Main Timeline: Vegetative Growth to First Bloom
Following germination, the plant enters its main vegetative phase, producing foliage and stems. This is the longest part of development, typically requiring ten to twelve weeks (70 to 85 days) from initial sprouting until the first flower bud opens. Seedlings started indoors are usually transplanted into the garden around the date of the last expected spring frost.
Sweet peas are climbing plants, requiring a support structure like a trellis or netting to encourage healthy vertical growth. Lack of support causes the vines to sprawl, slowing development and increasing disease susceptibility. Growers often “pinch” the growing tip of the main stem once the plant reaches four to six inches tall. Pinching redirects energy to side shoots, creating a bushier plant that yields a higher quantity of flower stems, though it may slightly delay the first bloom.
This growth phase thrives with long daylight hours and consistently cool temperatures, ideally between 45 and 68 degrees Fahrenheit. As days lengthen in late spring, the vines accelerate their growth, sometimes increasing their length by more than a foot per week. This rapid development signals the plant is nearing maturity and transitioning to flowering.
Influences on the Clock and Season Extension
External variables and maintenance practices influence the sweet pea’s journey to bloom or extend the flowering season. Temperature fluctuation is a primary factor, as sweet peas are cool-season flowers that struggle when temperatures consistently rise above 80 degrees Fahrenheit. Heat stress dramatically shortens the blooming period, causing the plant to prematurely focus on setting seed. In warmer regions, using a shade cloth helps keep plants cooler and prolongs flower production.
Nutrient management plays a factor, and sweet peas require a specific balance to encourage flowering over leafy growth. Providing too much nitrogen, especially as the plant nears its blooming phase, results in lush, green foliage but can delay or reduce the number of flowers. Instead, using a fertilizer with a higher proportion of phosphorus and potash helps support the development of buds and blooms.
The most effective way to extend the flowering timeline once blooms have begun is through diligent deadheading and continuous harvesting. If spent flowers are left on the vine, they form seed pods, signaling the plant that its reproductive cycle is complete and causing it to stop producing new flowers. By consistently removing spent flowers or harvesting the stems for bouquets, the plant is tricked into continuous production, sustaining the blooming season as long as the weather remains mild. Consistent moisture is also necessary, as water stress can cause the plant to stop rapid growth and cease flower production.