The Darlings of the Garden: Growing Sweet Peas from Seed

We've been sitting here trying to come up with a tongue-in-cheek approach to this blog post, but we're stumped. By all accounts, sweet peas are so innocent, delicate, and lovely; it's nearly impossible to find anything remotely appropriate to use as a springboard for a sufficiently obnoxious pun or two.

But we haven't given up yet. Fingers crossed.

Sweet peas are the ornamental cousins of the garden legumes we love to munch as part of our early veggie harvest. Where snow peas, sugar peas, and snap peas have similar adorable, lipped flowers and dainty, rounded leaves, sweet peas are bred for their beauty alone.

Or are they?

Background check!

Lathyrus odoratus means, in Greek, "fragrant pea." Lathyrus also refers to "pulse" crops in general, which by definition are legumes grown for their dried beans (though as you'll soon find out, that's not the case with sweet peas). All peas and beans belong to the expansive Fabaceae/Leguminosae (pea) family, which includes upwards of 20,000 leguminous herbs, shrubs, trees, and vines. This clan is the third largest of the flowering plants behind the orchid and aster families.

Sweet peas are native to southwestern Italy and Sicily, but due to their quick naturalization in similar temperate environments, they're often referred to as natives of the Aegean coast and islands, Sicily, Cyprus and Crete, and to southern Greece. The sweet pea is officially an invasive species in New Zealand and can become a problem anywhere it chokes out native or cultivated plants, but here in the United States, the plant doesn't raise any alarms. Some countries actually consider them to be "threatened," in large part due to people picking them from roadsides, ditches, and fields to use and sell in floral arrangements.

Toxicity warning

Okay, so maybe sweet peas aren't that sweet and innocent after all. The round, black seeds are mildly toxic to mammals. They usually pass through the intestines rather quickly, reducing the risk of poisoning, but chewed sweet pea beans or those eaten whole in large quantities will release compounds that lead to lathyrism, a nervous condition that causes reproductive failure, breathing difficulties, and paralysis of the lower extremities. The symptoms may also resemble rheumatoid arthritis.

It's rare that children and pets eat enough to become ill, but we recommend that you grow edible and ornamental peas in separate areas of your property, so it's easier for veggie-loving kids to know the difference. And since you asked, no. We haven't found any evidence that sweet pea beans shoved up a child's nostrils have the same effect as those consumed orally.

History and folklore

Sweet peas were first hybridized in the 17th century by a Scottish member of the Royal Horticulture Society named Henry Eckford. They gained popularity in the Victorian era, in part because botany nerds quickly made hundreds of colorful varieties from this plant which, in its wild state, is a vibrant violet hue. You'll find sweet peas in every hue and shade...except yellow.

As you might guess, there aren't any recipes for medicinal applications or down-home cookin' featuring sweet peas, but there are a few recipes for making poison from the seeds. (Nope, we're not sharing.) Practical Plants reports that essential oils distilled from sweet pea flowers were once used to create perfumes.

Sweet pea is the flower associated with April birthdays. In the Victorian language of flowers, sweet peas represent blissful and tender pleasure, appreciation, departure, and farewell. Therefore, in the modern-day language of flowers, the sweet pea represents a booty call followed by, "you gotta leave. I have an early meeting."

The French believed sweet pea bouquets strengthened the resolve and courage of a new bride, giving her luck and protecting her against strife...particularly that which is caused by nasty gossip about her purity. So...is it a leap to say that sweet peas shut down slut-shaming?

Sweet peas in the garden

Lathyrus odoratus has surprisingly strong winged stems bearing pairs of rounded, medium- to dark- green leaves. Curling tendrils at the ends of the stems allow sweet peas to climb upward or grab onto neighboring plants. Each orchid-like flower has five petals; from a distance, the blossoms look like folded butterfly wings, but up close you can see two large petals behind a "beak" of two smaller, downward petals. These nearly cover a tiny upward-pointing petal. These flowers grow from the main stem in loose clusters, and while there are tiny varieties as well as giants, the typical bloom is between .75" and 1.25" across.

Here are the quick facts:

• USDA Hardiness Zones: Cool-season annual in zones 2 through 11.
• Sunlight Preferences: Full sun; tolerates late afternoon shade where summer heat sets in early.
• Moisture Requirements: Medium. Keep evenly moist; if foliage wilts, increase irrigation.
• Soil Preferences: Rich, well-drained soil on the alkaline side with an ideal pH between 7.0 and 7.5.
• Plant Height: Climbs to 36" to 80"; without support, groups of sweet peas can grow to up to 5' tall and wide bushy mass.
• Plant Width: 24" to 36" spread.
• Growth Habit: Sprawling, spreading, mounding; climbs if provided support. Very fast grower!
• Bloom Period: May to mid-July; in temperate regions, a second crop can produce blooms in early fall.
• Bloom Colors: All shades except yellow. Bicolored varieties are common.

Grow these tender, floppy legumes in chaotic mounds, or provide them with structures to climb. Traditional wood slat trellises are a bit difficult for the sweet pea's delicate tendrils to grasp, but wire trellises, arched cattle panels, bamboo pole "tipis," and garden netting work very well. They're also perfect for covering up chain-link fencing. Suspend some knotted jute string on a wall or from your front porch eaves, or let the tendrils grab hold of the nooks and crannies in a stone or brick wall. Use them in hanging baskets and other containers, alone or as part of community plantings.

Just don't grow them so far away that you can't enjoy their strong, sweet fragrance.

Pests, diseases, and general maintenance

Though they're sun-loving plants, it's best to keep their roots shaded or lightly mulched. This will help retain consistent moisture.

If you're going for a mounded look, pinch off new shoots until you get the fuller shape you desire, then let them transition into the blooming phase. Bushier, denser sweet peas produce more abundant flowers. Use a diluted, nitrogen-heavy liquid fertilizer to encourage foliage, then switch to a high-phosphorous solution when the first buds appear. Or, simply feed them an all-around time-release fertilizer in pellet form if you've got better things to do.

Watch out for powdery mildew. If you water your sweet peas at soil-level and prevent the plants from laying on the ground, it's unlikely you'll have any problems. Avoid planting sweet peas where powdery mildew has infected past crops. As always, remove and dispose of any infected foliage; never toss it into your compost pile.

Insect and invertebrate pests include thrips, aphids, and caterpillars, though they rarely cause significant damage. Snails and slugs love young sweet peas and their shoots and may chomp on trailing tender foliage.

At the end of the season, you can mulch healthy foliage and dig it into the soil as green manure. If you want to take advantage of this plant's nitrogen-fixing abilities, Rhizobium leguminosarum is the correct bacteria for inoculating sweet pea seeds.

Harvesting

They rarely last more than a week as cut flowers, but while they're going strong, sweet peas are fabulous cut flowers. Pick them early in the day once the dew has dried, selecting flowers in all stages for the best effect. Immediately place them in lukewarm water; after a couple of hours, cut the stems once again under running water before adding them to your arrangement. This process will help reduce shock and maintain the flow of water up the plant's stem.

Use sweet peas as a single-species display or add them to informal groupings or bridal bouquets. They look best arranged in narrow vases, which help keep the bloom clusters bunched together. Be sure to change the water daily, and don't bother with the additives; they won't make a difference with sweet peas.

Growing sweet peas from seed

Whatever you may have heard, Lathyrus odoratus isn't all that difficult to grow from seed once you've followed a couple recommended steps. You can start them indoors in "four-pack" nursery trays or peat pots without the hassle of heat mats, but you'll want to use fluorescent lighting or a sunny window once the seedlings have popped above the surface.

Start them outdoors in loose soil. Remove any large clumps, and add plenty of aged compost and rotted manure. (Bonus points if you put a lot of banana peels in your composter; sweet peas love potassium!) Don't plant them in soggy beds; if you're expecting a lot of spring rain, add some sand and extra organic material to improve drainage.

• Seed Treatment: Scarify the seeds with an Emory board, and soak them for up to 24 hours in room-temperature water.
• When to Plant Outdoors: As soon as the soil can be worked in spring. The last frost is often too late for cool-weather peas.
• When to Plant Indoors: 6 to 8 weeks before last spring frost.
• Seed Depth: 1.5 times the seed diameter; roughly 3/4" deep.
• Seed Spacing: Plant them in triangles of three, with 2" to 3" between each point. Multiply and arrange these triangles as you see fit.
• Days to Germination: 10 to 21 days at 65°F.

Never let the soil around your seeds dry out when growing sweet peas from seed. Keep the soil damp by watering starts from bottom trays, and transplants and direct-sown plants at soil level. Harden off indoor starts for about 10 days before you plant them in the soil.

Start your season with Seed Needs

So maybe sweet peas aren't the symbol of everything sweet and pure. So what? We like our flowers a little on the feisty side, and we love having our first impressions challenged with a little history.