In USDA hardiness zones 8,9, and 10, sweet pea seeds can be sown in the fall for early spring germination. These areas have mild winters that allow the seed to reliably sprout in the early spring.
To do this cultivate your planting bed in the fall. Add compost, remove weeds, and moisten the soil. Scatter sweet pea seeds across the bed, or plant them at approximately 1-inch spacing. If the bed backs up to a trellis for support, plant in one or two rows along the trellised edge.
Cover seeds with 2 inches of soil and then mulch them through the winter. Check them in the spring. If the mulch has broken down enough, they will be able to sprout through it. Otherwise, you’ll have to rake back the mulch so they have a chance to establish themselves.
Direct Sow in Spring
Traditionally sweet peas are sown directly in the ground from seed in the early spring. Do not wait until the last frost has passed, plant 4 weeks before the last frost in your region. Planting sweet peas too late will result in shorter plants and fewer flowers.
As soon as the soil can be worked, prepare your planting area by removing mulch, weeds and loosening the soil. Plant seeds at 1-inch spacings and cover with 2 inches of garden soil or finished compost. Keep the soil moist.
Some optional tips for sweet pea planting:
- Soak seeds overnight prior to planting to speed germination
- Innoculate soil with rhizobial bacteria from garden supply store
- Add bone meal or a high potassium organic fertilizer to the soil
Starting Plants indoors
In especially cold climates it may be necessary to start sweet peas indoors. Gardeners in all areas can get a headstart on the season by doing this. Sow seeds indoors or in a greenhouse 6-8 weeks before the last frost in the region.
Prepare 4-inch garden pots or planting trays with a depth of at least 4 inches. Peas tend not to transplant well, avoid them becoming rootbound in a pot by using large enough containers. Fill with an all-purpose potting soil, if you would like to you can mix some compost into it. Avoid nitrogen heavy soil mixes or fertilizers, peas do not require nitrogen and can suffer if over-fertilized.
Plant seeds 1 inch deep and 3 inches apart. Keep the soil moist and warm, ideal germination temperature is around 65°F (18°C).