Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Do you love sweet peas but find them difficult to grow? The secret to growing them is cool temperatures. Although they are only distantly related to peas, treat them like your cold hardy peas and you’ll have thriving vines in no time.
What are Sweet Peas?
Sweet peas (Lathyrus odoratus) are an annual flowering vine. They were discovered on an island off the coast of Sicily in 1699 by Father Cupani who was a botanist as well as a monk. He sent seeds to a friend in England. The original sweet peas had a scent which is described as similar to honey and orange blossoms and unremarkable purple flowers so it wasn’t until 1870 that they attracted the attention of a Scotsman, Henry Eckford, who began hybridizing them, eventually creating 115 cultivars. They were a sensation in Victorian gardening circles.
In 1901, an even showier hybrid appeared in the garden of the Earl of Spencer. And the race was on to create fancier hybrids. As so often happens in hybrids, the fancier hybrids lost their sweet fragrance but the English gardening public was more interested in the flower than in the scent.
How to Grow Sweet Peas
Sweet pea vines vary in height from 3 to 6 feet depending on the cultivar. They grow best in full sun (6 to 8 hours daily) but like their roots to be shaded. It’s helpful to grow short annuals around the base of your sweet peas to shade their roots and keep them cool. A thick layer of mulch will also help to keep the roots cool. The flowers come in every color except yellow.
The vines need something to climb on. A trellis or tepee works well, but even just upright sticks, called "pea sticks", pushed into the soil will do. The tendrils which the vines use to climb cannot “grasp” anything thick, so use a netting if you have thick fence posts. Chicken wire may be ugly but sweet peas will readily climb it. Some gardeners even encourage their vines to ramble over the other plants in their gardens.
How to Grow Sweet Peas From Seed
For best germination, either soak your seeds for 24 hours before planting or “nick” them, i.e. make a small cut in the outer shell of the seeds being careful not to damage the embryo inside, to allow moisture to enter the seeds and start the germination process.
Sweet peas grow best in cool weather. In zones 7 and warmer, plant your seeds outdoors in the fall after Labor Day or very early in the spring. Zones 6 and cooler you can either start your seeds indoors 6 to 8 weeks before your last frost and set them out in the early spring or direct sow the seeds in the early spring as soon as the soil is workable.
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Plant the seeds 1 inch deep and 2 to 3 inches apart. Germination should occur in 7 to 15 days. When the seedlings are several inches tall, thin them to 6 to 8 inches apart. Overcrowding will result in stunted growth and encourage the spread of disease. Thinning your plants allows for air circulation which will prevent problems with mildew.
Birds can be a problem until your seedlings are 4 to 5 inches tall. Cover your plants with netting as you do your strawberry plants or simple invert small plastic strawberry baskets over them until they grow tall enough to no longer draw unwanted attention from the birds.
If you wish to fertilize, use a balanced fertilizer. Too much nitrogen encourages foliage growth and discourages flowering.
Sweet peas need 50 days of temperatures below 60⁰F to bloom well. They stop blooming when the temperatures rise above 65⁰F. If you wish to harvest the flowers for a lovely bouquet, the best time is early in the morning before the dew dries when they have the most scent. Choose stems where the lowest buds are just beginning to open. The rest of the flowers will open after the stems have been cut and arranged. Harvesting the flowers also encourages the plants to continue to bloom rather than going to seed.
© 2017 Caren White
Caren White (author) on March 05, 2017:
I wonder if the wild sweet peas in Spain are related to the original wild sweet peas from Italy that were developed into the domesticated sweet peas that we grow in our gardens today?
Anne from United Kingdom on March 05, 2017:
I´m British so have grown up with sweet peas and they are lovely. I cannot grown them here in Spain where I now live, its just too hot for them, but I have found little wild sweet peas growing in an untended olive grove among the grass and wild flowers. They don´t attain the height of cultivated/ hybridised varieties and had no scent ( that I can remember) But were a lovely deep purple colour.
I will remember your tip to nick or soak the peas when I return to the UK and start growing my own.
Marlene Bertrand from USA on March 04, 2017:
This article is such a big help to me. I have not had much success with sweet peas. It could be because I don't soak or nick the seeds. Excellent tip. I think I will try it.