When it comes to planting annual flowers by seed, it doesn't get much easier than the sweet pea. Sweet pea seeds are a cinch to plant, and once sprouted, the sweet pea plants provide masses of colourful flowers that will bloom with minimal care until the summer heat arrives. Sweet peas are old-fashioned bloomers available in both vining and bush varieties with either single or double blooms. Some varieties have a sweet scent.
Plant sweet pea seeds outdoors as soon as the ground can be worked in late winter or early spring, or about six weeks before the last expected frost date in your area.
Prepare a sunny spot in your garden. Spade the soil to a depth of 12 to 18 inches, and then work in 4 to 6 inches of organic matter such as compost, dry leaves, finely shredded bark or manure to enrich the soil and improve drainage. If possible, spade the soil in the fall for spring planting.
Add a balanced, slow-release fertiliser to the soil before you plant sweet pea seeds. Use a balanced fertiliser with a ratio such as 20-20-20. Apply the fertiliser according to the directions on your fertiliser package, as rates of application will vary. Don't over-fertilise, as too much fertiliser will result in green, leafy sweet pea plants with very few blooms.
Use a trowel to dig small holes for the sweet pea seeds. Plant two to four sweet pea seeds 2 inches deep in each hole. Allow 5 to 6 inches between each hole.
Water the soil deeply, and then keep the soil moist until the seeds germinate, usually in two to three weeks. Continue to water the sweet pea plants regularly. Keep the soil moist, and don't allow it to become completely dry.
Provide a sturdy support at planting time if your sweet pea seeds are a vining variety, as the vines can grow 5 to 10 feet long. Install a trellis, or string twine or string between two stakes. Bush varieties grow only 8 to 24 inches tall and require no support.
Thin the sweet pea seedlings when the plants are 3 to 4 inches tall. Snip off the weak seedlings so that you have one sturdy plant every 4 to 6 inches.
Spread 4 to 6 inches of mulch around the sweet pea plants after thinning. An organic mulch such as shredded bark or dry grass clippings will keep the soil moist and cool.
Snip flowers for bouquets as soon as the flower appear. Cutting a few sweet pea blooms every other day will encourage the plant to continue blooming as long as possible.
Cut sweet pea flowers can last up to a week if you provide a vase full of fresh water every day. Snip 1/4 inch from the bottom of each stem when you change the water.