How to Grow Sweet Peas From Seed Indoors

Have you dreamed of having a garden full of good old-fashioned sweet peas? I’ll share my tips on sowing sweet pea seeds indoors, how to transplant them into the garden, and much more.

Sweet Peas Lathyrus odoratus

• Annual hardiness zones 7 up
• 6 hours morning sun
• Well-draining soil

There are so many reasons I love growing sweet peas year after year…

Vibrant Colors and Abundant Varieties

When you grow your sweet peas from seed, you have an abundant amount of colors and mixes available to choose from. The biggest challenge will be trying to decide which sweet peas you’re going to grow in your garden every year.

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Note: I am not a Master Gardener, but a self-taught hobby gardener who shares my opinions and what has worked for me in the garden.

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The Sweet Smell of Every Bloom

I don’t know about you, but sweet peas are my favorite scented flower. This is one of those times when I wish there was such a thing as a “scratch and sniff” blog post, where you could take in the most incredible fragrance that comes from these beautiful blooms. The open-pollinated heirloom varieties are best known for their amazing fragrance.

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The Perfect Cutting Flower

With their stunning colors and long straight stems, sweet peas are the perfect cut flower for any late spring or early summer bouquet.

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When to Grow Sweet Peas

In the warmer regions where winter weather is milder (zone 7 and above), sweet peas can be sown in the fall. For everyone else, you’ll sow your sweet pea seeds in late winter or early spring. They like cool roots and temperatures and can be sown indoors 10-12 weeks before the last frost of the season, which for my area is around April 18th.

Sweet peas can also be sown directly in the ground as soon as the soil can be worked in the spring. The optimum soil temperature for sowing sweet pea seeds is 55-65°F. Make sure to watch for birds, snails, slugs, and other pests, they love sweet peas!

Note: Sweet pea seeds are poisonous if ingested. Use caution around children and pets.

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Supplies to Sow Seeds

• Sweet Pea Seeds
• Seed Starter Potting Mix
• Containers (that will accomodate deep roots)
• Drainage Tray
• Plastic Dome Lid
• Labels

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Steps for Sowing Sweet Peas

Step 1 – Soak Seeds in Water

In order to speed up the sprouting process by a few days, soak the seeds in water for 24 hours before sowing to soften the seed coat. This process can be done for indoor and spring sowing. There’s no need for fall sowing though.

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Step 2 – Choose Container

Sweet peas produce an abundant amount of roots, so use the deepest pots you can find. I usually use 4-inch pots, or you can use root trainers as well. The more room you give the roots at the beginning stages of the seed starting process, the better the plant will grow in the long run.

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Step 3 – Fill Containers with Soil

I would recommend using a good quality seed starting potting soil when sowing your sweet pea seeds. Good soil will make all the difference in the world. The soil should be moistened before adding it to the container.

BENEFITS TO USING A SEED STARTING MIX

• Helps to germinate quickly
• Holds the moisture
• Allows the roots to penetrate down into the garden soil quickly.

You can make the mix go even further by filling the bottom half of the container with regular potting soil and then filling the rest of it with the seed starting mix, where the seeds are going to be placed.

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Step 4 – Sowing the Seeds

Sow 2 seeds per container or cell by creating a 1-half-inch hole into the soil, in 2 opposite corners. You can use a pencil, dibbler, or even your finger to make a hole.

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Step 5 – Bottom Water

Bottom watering is the most gentle and easy way to water your sweet pea seedlings. Fill the drainage tray with about an inch of water and let the container sit in the tray to evenly moisten the soil. DO NOT leave the container in a tray full of water for more than an hour.

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Step 6 – Cover

Covering your container with a plastic dome lid will increase the humidity and speed up the germination process.

Place in a cool greenhouse or in a bright window in the house.

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Once the Sweet Peas Have Germinated

Uncover the Container

Take the plastic lid off the container once the seeds have germinated.

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Pinching

Once the sweet pea plant is 4-6 inches tall and has at least 3 sets of leaves on each stalk, start pinching it back to encourage side shoots. Pinching not only encourages the plant to actively branch from the base, but also produces more blooms. Snip off the central growing tips just above leaf joints and continue this throughout the growing season.

Preparing the Garden Beds

When planning the location of your garden beds, keep in mind that sweet peas love the full sun in the northern half of the US, and afternoon shade in the southern states.

Provide Nutrients

Sweet peas are heavy feeders and need extra nutrients. When preparing the garden beds for transplanting, add a layer of compost or bone meal, and natural fertilizer. Mix these ingredients deep into the soil.

You can read more about preparing your garden for seedlings HERE.

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Provide a Structure for Sweet Peas to Climb

Sweet pea vines will grow quickly and at least 6 feet tall, so they’ll need a strong structure to climb on. Setting up a structure, like a trellis, before the sweet pea vines start growing, will not only be easier but will less likely damage your plants.

Tall wooden or metal posts with metal fencing attached will allow the vines to climb up them. I use cattle fencing or chicken wire.

As the sweet peas continue to grow up the trellis through the season, tie the vines to the structure. I use twine. They can grow more than a foot a week during the prime growing season.

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Transplanting Sweet Pea Seedlings to the Garden

Transplant the sweet pea seed starts to garden beds around the last spring frost. Plant in two rows, one on each side of the trellis, spacing roughly 8 inches apart, down the row.

Watering

Sweet peas need a lot of water to thrive, especially during warm weather. I set up soaker hoses as soon as they’ve been transplanted to their new home in the garden.

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Feeding Plants

Feed plants weekly with diluted fish and seaweed emulsion.

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Caring for Your Sweet Peas

To prolong blooming, harvest and deadhead flowers frequently to keep the plants from setting seed. Deadheading is the process of trimming back the old flowers, encouraging new growth.

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Harvesting

For the longest vase life, pick when there are at least 2 unopened flowers at the tip of a stem. Sweet peas are a short-lived cut flower, and will usually last only 4-5 days in a vase. Add a flower preservative to the water to extend vase life.

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The most common mistakes made when growing sweet peas

• Forgetting to add support at the time of planting outdoors. It’s difficult to add support after the sweet peas have already started to grow.
• Not adding compost or fertilizer to garden beds with poor soil. This will result in less bloom production and weaker plants.
• Planting too close together without thinning them. This can create powdery mildew and crowding, which reduces the plants flower production.
• Waiting too late to plant them. Sweet peas don’t like the heat and won’t produce as many flowers.

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Sowing Seeds Without a Greenhouse

You don’t have to have a greenhouse to sow seeds. My friend Stacy at Bricks ‘n Blooms shares everything you need to know about sowing seeds indoors. Make sure you visit her blog post for more!

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Have you grown sweet peas in the garden? I’d love to hear from you in the comments below.

Until next time,

Happy Gardening!

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