Texas Cooperative Extension,
Texas A&M University, College Station, Texas

March 2005

Sweet Peas, Continued

by the National Garden Bureau


Timing by Region

Sweet peas are one of the easiest flowering annuals to start from seed. Sweet peas are commonly direct seeded in the garden. Give them a site with full to partial sun and deep, rich, loamy, moist but well-drained soil. Add plenty of organic matter (compost, well-rotted manure, leaf mold, or humus) to enrich the soil and make it more friable.

Sweet pea 'Pastel Sunset'
'Pastel Sunset' sweet pea
Sweet peas are most successful when they are started at times with cooler temperatures. Each region has its own unique "season" for growing sweet peas. In western North America, sweet pea seeds should be sown from August forward to maximize winter and spring flowering. Although sweet peas can be killed back by hard freezes, they are reasonably cold hardy and can take frost without much damage to plants. Cooler night temperatures extend the enjoyment of sweet pea flowers in the west into the summer months.

In the drier plains states, sweet peas can be started early indoors for transplanting or sown directly after the harshest weather has passed. Cut flower growers in Colorado have successfully grown sweet peas through high summer temperatures by mulching heavily as plants mature and weather heats up.

In the south, sow seed in November or December for early spring fresh cut flowers. In the mid-west and northeast non-coastal areas, sow seed indoors in February and transplant into the garden when the ground thaws. Alternatively, seed can be sown directly into prepared garden soil in April. Finally, the coastal areas of the northeast are excellent areas to grow sweet peas for spring use.

Sowing Seed

Sweet peas will need about 50 days of cool temperatures (under 60ļ F) to bloom gloriously in your garden. Sweet pea seed has a hard, water insoluble seed coat. There is no evidence that soaking sweet peas will increase germination. Nicking the outside coating of a sweet pea seed will allow rapid hydration of seeds and does both speed and increase germination. Nicking can be easily accomplished by using a nail clipper to score the sweet pea seed coat. Sweet pea seed will germinate in soil at temperatures of 55ļ to 65ļ F or 13ļ to 18ļ C.

Plant seeds in holes that are about two inches (two knuckles) deep. Drop two to four seeds per hole, with holes spaced four to six inches apart. Water thoroughly and keep soil moist until seeds have sprouted. Expect germination in about 10 to 21 days. Once the seedlings are growing, water regularly to promote strong, healthy growth. When the seedlings are three to four inches high, thin them out, leaving the most vigorous-looking plants four to six inches apart. Sowing seeds each week over several weeks will further extend the time you get to enjoy your sweet peas. Grow them in peat pots or four-inch plastic pots filled with a soil free seed-starting mix. Sow two or three seeds per pot - pushing each an inch down into the potting mix. Cover with mix, water, and put the pots in a cool, dark place. After about 10 days, keep an eye out for new shoots emerging above the soil. At that point, bring the plants out into the light. Keep them in a cool place (below 55įF.); if they are coddled in a warm room, they wonít be tough enough to transplant outdoors without a lengthy hardening off period. When the seedlings have two sets of real leaves, thin to one plant per pot. Transplant into the garden about a month before the last frost date, as soon as the soil is workable - the shoots are tough and wonít be bothered by light frost. Allow 6 inches between climbing varieties, 12 inches between dwarf bushy types.

When planting tall, long vine sweet peas, itís best to place the stake or support in the ground at the same time as the seed or transplants to avoid damaging the roots. Trellises are the most common supports, yet there are other climbing options. Bird netting strung between two stakes, string, twine, or fishing line hung from the top of a split rail fence, a bamboo teepee, brush stakes - all are good verticals for sweet peas to climb. Unless the support is up against a wall, sow seeds on all sides, producing an eye-catching array of blooms that can be seen from all directions. Once the plants have been thinned, mulch them well; a four- to six-inch layer of organic mulch will keep the roots cool and extend the growing season.

Garden Care

Do not over fertilize or youíll wind up with very deep green leaves but few flowers. A balanced 20-20-20 slow release fertilizer blended into the soil at planting time works fine for the initial plant development. Alternatively, organic fertilizers are also excellent for sweet peas. Additional mulching with composted manure will help retain soil moisture and provide nutrients for strong plant growth and flowering.

If blooms are not cut regularly, deadhead the plant as soon as flowers fade. Allowing the plant to produce seedpods will reduce overall flower production. Removing spent blooms will ensure more blooms.

Possible Problems

The first challenge for sweet peas, like other direct-sown seeds, is to avoid being plucked out of the ground by voracious birds, mice, squirrels, and other critters. As seedlings, sweet peas are vulnerable to birds, slugs, and snails, especially if fall-planted in a warm climate. Preventative measures often deter a problem before it has a chance to get started. Follow these guidelines for healthier plants. Plant sweet peas in an area that gets good air circulation. Water early in the day so the leaves are dry by nightfall; wet leaves are a magnet for fungus. Think of sweet peas like food crops. Rotate planting areas so that the sweet peas are grown in the same space once every four years. Donít grow sweet peas where other legumes are growing or grew last year. Legumes include garden peas, beans of all types, peanuts, and clover.

How to Grow From Purchased Plants

You may find sweet peas sold as plants particularly at some specialty nurseries or garden centers. There may be ready-made container plantings of sweet peas - an instant garden. Sweet peas need tender care when transplanted, so look for plants in individual earth friendly pots or peat pots. The larger the pot, the better. Right before planting, snip off any flowers or flower buds. This is the time to get the roots well established so they can support the growing plantís needs. Even though you sacrifice early blooms, youíll be rewarded with bigger plants with an abundance of larger flowers.

Plant into prepared garden soil or a container. With transplants, itís even more important to plant the support before digging the plant in to keep the precious roots out of harmís way. Try to keep the root ball together. Plant it at the same depth as it was originally growing. Lightly firm the soil around it and water. Wait a week to ten days before mulching. Be sure to keep the mulch at least an inch away from the stem of the plant until plants are well established. Otherwise you could smother the stem or be likely to encourage insects, pests, and diseases.

Container Culture

The introduction of 'Cupid' - the first dwarf sweet pea - at the turn of the 19th century brought sweet peas into the realm of containers. Their diminutive size suits hanging baskets, window boxes, pots, urns, and all other sorts of containers. There are many dwarf sweet pea types available from mail order catalogs or in seed packets purchased at stores. Climbing sweet peas also make great container plants. Instead of sowing one or two seeds at the center of the container, make a circle of seeds - spaced a couple of inches apart - an inch in from the rim of the pot. In the limited space of a container, itís easiest to plant the support and then sow the seeds around it. For larger containers, tomato cages are perfect supports; the legs can be pushed into the potting mix. Since sweet pea shoots arenít bothered by frost, you can set a container of sweet peas out in the garden in early spring (at the same time youíd plant seeds outside.)

Bring the Outdoors In - Container Plants

When the first flowers appear, start cutting flowering stems for indoor bouquets. In addition to adding the sweet perfume in the house, youíre encouraging the plant to produce more flowers. Cut stems every other day, early in the morning when they are the freshest. For climbing varieties, thinning lateral shoots that start at the base of leaves will reduce vegetative growth, increase flower production, and encourage better air circulation around the plant.

The stems will look full when you first arrange them and the remaining buds will open as the first blooms fade. Be sure to remove any leaves that are below water level in the vase. A bouquet of sweet peas can easily last a week indoors if you cut off 1/4 to 1/2 inch at the base of each stem and change the water daily.

This material is reprinted courtesy of The National Garden Bureau. Cathy Wilkinson Barash is the author of this fact sheet. Sweet pea image 'Pastel Sunset' courtesy Renee's Garden; Sweet Pea 'Ocean Foam' and 'Streamers Mix' courtesy Bodger Seeds Ltd.