Sow seed in cool weather
Sweet-pea seeds will germinate at a rate of between 78 and 90 percent. To enhance germination, nick the seed coat so moisture can more easily penetrate the protective barrier.
Photo/Illustration: Jennifer Benner
There are a few commandments to follow to successfully grow sweet peas. Plants must have soil with excellent drainage and full sun to partial shade. Sufficient spacing of plants for good air circulation is important, too, because sweet peas are susceptible to mildew. Young seedlings must also be protected from slugs, snails, and marauding birds until they are 4 to 5 inches tall. Most important, seeds must be sown and grown in cool weather.
In areas with mild winters and hot summers, sweet peas are best sown in fall, after Labor Day. This gives the seeds time to germinate and to develop good root systems, which help the seedlings overwinter and grow rapidly once spring weather and longer days arrive. If you forget to plant in fall, sow the seeds as early as possible in spring in an area with some afternoon shade. In regions with mild winters and relatively cool summers, like the Pacific Northwest, sweet peas can be sown later in spring for late-summer bloom.
In areas with cold winters, sow sweet peas indoors and then transplant them outdoors when weather permits. Sow the seeds in individual 3- to 4-inch-diameter containers to keep the roots from being disturbed while transplanting. It’s important not to plant seedlings in the garden any deeper than they were in containers. If summer heat or humidity comes on fast in your area, direct-sow seeds as soon as the ground can be worked in spring in a spot that gets some afternoon shade. Sweet-pea seedlings are fairly tough and can take a light frost, unlike many other annual seedlings.