When to Plant Sweet Pea



I live in Windsor Ontario, I believe zone 7a. I am planting sweet peas this year. What would be the best method? Sow outdoors in early spring or start indoors? I plan on planting in an area that is west facing and gets a lot of sun in the late afternoon.


Thank you for your question. Your Sweet Peas maybe a Lathyrus odoratus cultivar, which are wonderfully fragrant climbing annuals. There are also several perennial cultivars available including the broadleaf Lathyrus latifolius, which lack the perfume. If you haven’t bought seeds yet, check to see if the varieties available to you are early or late blooming. By mixing the two you can extend your flowering period.

Sweet peas are slow to germinate so starting them indoors is a good way to get ahead for the season and maximize your flowering period. Although they can tolerate light frosts, sweet peas can be destroyed by the late winter snowfalls and freezing temperatures that we can experience in Ontario. The last frost date for London, Ontario is May 10, 2019. Expect your seeds to take about 6 weeks to germinate. This means you should plant your seeds by March 29 at the latest.

Biodegradable pots are easy to use if you can find the right size. This allows you to transplant your seedling with the pot for an easy transition to the garden, without disturbing the long, delicate roots. If you are using plastic pots try to find tall, narrow ones that are at least 6 inches deep. Sweet peas like their roots to grow deep into moist, nutrient rich, well draining soil.

Plant your seeds 1 cm (3/8 inch) deep and 5 cm (2 in) apart in a free draining potting mix, then cover with a one inch layer of good quality compost. Sweet peas are heavy feeders and enjoy even moisture, so water as soon as the topsoil begins to dry.  The readily available moisture and indoor temperatures help to erode through the seeds tough coating. If you miss the planting date, or wish to speed up the process by several weeks you can also soak the seeds in water for 24 hrs prior to planting. This way you can plant only the swollen seeds and discard the non viable ones. Some varieties have dark, very hard seeds which require ‘chipping’ before sewing. Cut or file a small notch in the seed coating opposite the eye of the seed,  then soak in tepid water for several hours before sewing.

Sweet peas like to germinate in cooler temperatures, so find a spot indoors that is away from direct heat sources. Ideally, they prefer to grow at 12-18 degrees celsius. Until they sprout through the surface of the planting mix they don’t require much light.

Once they sprout, pinch off the stem just above the second pair of leaves and move them into a position with more light if necessary. Also, pinch off any flower buds that develop before you have planted your seedlings outside.

When the ground is dry enough to plant outside, its time to harden off your seedlings. By May 10 you can start moving them outside to a site protected from direct sunlight or strong winds. Leave them for an hour day 1, then bring them back inside. Each day leave them outside for an hour longer. After a week they should be ready to transplant into your garden.

Add some bone meal and compost to the growing bed. Plant your seedlings 15 cm (6 inches) apart and water gently. Avoid overhead watering. Fertilize every two weeks with liquid fertilizer or top up the bed with a small amount of compost throughout the growing season. Provide a trellis or obelisk for growing support.

Mulch is important to protect your plants roots from the summer heat, especially for your west facing bed with its hot afternoons. It will help reduce the evaporation of water. If you choose a natural or organic compost it has the dual benefit of conditioning your soil while it is retaining moisture.

Pick your flowers regularly to enjoy the scent and colourful blooms inside, and it will extend your flowering season. Good luck!