Master Gardener: Flowering sweet peas (Lathyrus odoratus)  |

Master Gardener: Flowering sweet peas (Lathyrus odoratus) 

Sandy Kent
For Steamboat Pilot & Today
Flowering sweet peas plants should be started inside in March.
Pater Alfino/Courtesy photo

People grow sweet peas for their beautiful color and scent. Sweet peas are an ornamental flower that is not edible. It’s poisonous if ingested in large quantities.  

Start sweet peas by sprouting them in the house in the middle of March. To begin, place them in an  uncovered jar with water, changing the water when it gets cloudy. Another option would be to sprout sweet peas by placing them in a plastic bag with a damp paper towel. The trick is to keep them moist, but prevent them from developing mold or rot. Place the jar or plastic bag in a dark cabinet.  

As soon as the sprout forms you will want to plant one seedling each in a two- or three-inch pot. Labeling each pot with the name of the plant and color will aid you when it comes time to plant outdoors.

Once planted in the pot, let the seedlings grow in a greenhouse or under grow lights until early May. As soon as they get 6 inches tall, cut the growing tip above the first two sets of leaves to encourage branching. Sweet peas are hardy and can tolerate a moderate frost. A week or so before I plan to plant  them outside, I “harden them off”. The seedlings have been in a protective environment (indoors or a greenhouse) and need to be introduced to the outside world of wind, cold and harsh direct sun. To harden off your sweet peas, place them in the shade outside for a few hours each day gradually introducing them to the sun. This will take about a week. 

Now it’s time to plant. Pick a sunny location where a strong trellis can be installed. Sweet peas need support and you can use strong trellis netting or chicken wire, about 6 feet high, stretching across the entire area in which you want them to grow. When planting your flowers, make sure you have access to the trellis so you can cut the sweet peas on both sides.

Soil health is really important for sweet peas. They like garden loam with plenty of compost. You will want to add a well-rounded all-purpose fertilizer (5-4-5) when planting. 

Sweet pea roots are large and need plenty of room to grow so make sure you plant them 8 inches apart. Planting them closer will end with shorter flower stems. Once they start growing, coax them to grow up the trellis. Use garden twine to encourage each plant to reach the bottom of the trellis. Sweet peas don’t like to dry-out, keep them well watered.

I asked our local Flower Farmer, Lisa Godbolt of Garden Goddess, about fertilizing sweet peas during the growing season.

“I spray with compost tea weekly before they start blooming. Adding the compost/well-aged manure before planting is more important,” she said. “If you do fertilize, use a fertilizer high in phosphorus as too much nitrogen will encourage more foliage, not blooms. So emphasize compost or well-aged manure, lots of water and continuous cutting for successful growing!”

Cut sweet peas in the morning, before it gets hot. The more you cut sweet peas, the more they bloom. You want to prevent the plant from putting energy into making the seed pod as the pods are poisonous.  Sweet peas can last up to five days in the vase and once they start blooming you can cut a bouquet  everyday.

Interested in starting your own garden or improving your existing garden? Join the Routt County CSU  Master Gardeners at the Bud Werner Memorial Library on April 25 and 26 from 5-7 p.m. Expert gardening advice to help you plan and maximize your summer garden. Learn the best ways to leverage our short growing season and challenging soils.

Sandy Kent is a CSU Master Gardener from the class of 2020. With the help of her husband Mike (under-gardener), she enjoys growing flowers and vegetables on her mini-farm.

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