How to Grow Sweet Pea Flowers & What to Avoid

Use these tips to grow sweet pea flowers (Lathyrus odoratus) from seed in your garden in spring or a greenhouse in fall. With the right growing conditions and care, these old-fashioned flowers will provide beautiful blooms throughout the summer.

For other favorite flower growing tips see 7 Best Tips for Growing Zinnias and When to Plant Dahlias.

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How to Grow Sweet Peas

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Contents

• 10 Best Tips for Growing Sweet Peas
• Frequently-Asked Questions
• Summary
• Resources

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10 Best Tips for Growing Sweet Peas

1Know What You’re Growing

Annual or Perennial

Annual sweet peas (Lathyrus odoratus) are the single-season beauties we know and love.

In many areas of North America, the perennial sweet pea (L. latifolius) is an invasive problem, clogging open fields and roadsides. It looks pretty until you realize it’s crowding out other plants and acting like a thug.

When buying your seeds, be sure the packet says they are annual seeds suitable for your growing zone.

This explains more about the difference between annuals and perennials.

Annual Sweet Pea Seeds

Sweet Pea Seeds | Botanical Interests (US Shipping)
Sweet Pea Seeds | West Coast Seeds (CAD Shipping)

Dwarf flowers or vines

If you want climbers that grow up a trellis, or hang down from a hanging basket, choose annual vines. Many grow 5 to 6-feet tall.

If you want short, stout (but beautiful) flowers, choose an annual dwarf variety. Heights vary from 6 to 18-inches.

Is fragrance important?

Love the fragrance? The older, heirloom open-pollinated varieties may be just what you’re looking for. They are best known for their fragrance. Some of the hybrids, as well as the invasive perennial, have no scent.

This explains the differences between heirloom, hybrid, and open-pollinated seeds.

Related: 10 Flower Growing Secrets & Common Mistakes

2Get Your Timing Right

Overall, sweet peas prefer cooler spring-summer temperatures and don’t do well in intense heat.

You can start your plants from seed or buy starter plants and transplant them after last frost.

Late Winter or Spring Sowing

There are a few options for timing your seed starting:

1   Start indoors late winter / early spring (8-10 weeks before last frost).
2   Sow directly outdoors early spring (6 weeks before last frost).
3 Around or after last frost: sow from seed if time (and temperatures) permit or grow from established plants. You need enough frost-free days for flowers to form.
4   Sow directly outdoors in autumn: recommended for mild winter climates where the ground does not freeze.

Fall Sowing

If you have a greenhouse that neither dips below freezing nor gets too hot, you can also start your sweet peas mid-fall. Use root trainers if you can so, by spring, the young plants have nice-deep roots.

If your climate allows it, you can also get a jumpstart on the season by growing “winter flowering” sweet peas that bloom if 10-hours of sunlight is available each day. Others need 11,12 or more hours of light.

3Prepare the Seeds Before Sowing

Every gardener seems to have their own preferences when it comes to preparing sweet pea seeds for sowing.

Some feel the seeds need a lot of prep, while others direct sow them and everything grows fine.

Here’s what may be needed. You can always test some each way and see what works for you.

Sweet pea seeds have a tough coat. To speed up germination, we ‘scarify’ the coat, which means nick it or rough it up to enable water penetration.

We do this for indoor and spring sowing. There is no need with fall sowing (zone 7 or warmer): nature gradually does it for us.

I confess I often forget to prepare the seeds sometimes and they (mostly) still sprout but I do prefer to do this to ensure best possible germination rates.

There are a few ways to prepare the seeds:

1   Rub seed coat with sandpaper or a small garlic grater, or nick with nail clippers. You want to score the brown seed coat without damaging the inner seed.

And/or

2  Soak seeds in moist paper towel 12-24 hours or a jar of warm water for 1 hour minimum.

Soaking the seeds causing the seed to swell and the seed coat to soften. Some gardeners say it takes just 30 minutes of soaking while others prefer 24 hours. I’ve had some seeds to turn to mush after 24 hours so I prefer somewhere in the middle.

This has step-by-step instructions to test any garden seeds for viability and germination rates.

4Choose a Prime Growing location

Here in Ontario, Canada, we have hot, humid summers. The best location for sweet peas provides approximately 6 hours of morning sun, and dappled shade for the afternoons when the sun is quite fierce.

The planting area needs well-draining soil amended with lots of compost or composted manure. Sweet peas do not like damp or dry conditions and are heavy feeders.

5Sow Seeds at Right Depth and Distance

This is simple but it can make a difference. Be sure to sow at the correct depth. Your seed packet will confirm the recommended amount.

Generally, sweet pea seeds should be sown just one-half to one-inch deep and spaced 4 to 6-inches (10 to 15 cm) apart. They must have darkness to sprout.

Sown too deep, they may not germinate. Sown too close to the surface, the critters will get them or they will dry out without germinating.

Germination typically takes 2-3 weeks and the plants will have mature flowers 75-85 days after that.

6Protect Seeds from Critters

You’ve got this far. Now take the extra step and protect those seeds and seedlings from all the wild things. Sweet peas are not edible for humans, but that doesn’t stop the birds, snails, and slugs from wanting them.

My favorite option for protecting newly-sown seeds is fine wire cloches that sit right over the planting area and allow room for growth inside.

The least expensive option that works nicely is to use wire waste baskets from the dollar store.

The critters stay out but sun and rain still get in.

Once the sweet peas are about 4 to 6-inches tall, they are less vulnerable to pests and you may be able to remove the cloches.

If pests are a big problem (e.g. you have relentless slugs or snails), growing in large containers may be a better option. This has more tips on dealing with slugs and snails.

I offer no solution for deer or ambitious rabbits. The best option for deer is fence taller than they can jump.

7Add Trellis Right Away

It’s much easier, and less likely to damage your plants, if you get your trellises in place before the vine grows.

Use trellis, hardware cloth (lead-free or stainless steel), netting, or stakes.

In the first month of growth, the vine will need your help to guide it onto the trellis with twine or clips. Check every other day.

After that time, tendrils start to form and grab hold. You do still need to make sure the plant is growing as desired and not wandering off or getting entwined on itself.

Some gardeners snip off all the tendrils and tie the plants instead. The advantage is that you won’t have the tendrils grabbing onto the rest of the plant which can otherwise create a tangled mess.

8Pinch and Remove Tips for Bushier Growth

Congrats! Your sweet peas are on their way.

If you’re growing vine varieties, it’s time to decide if you want tall, thin vines, or bushier plants with more flowers. The difference is regular maintenance.

Once the plant has at least 3 sets of leaves on each stalk, you can start pinching it back to encourage side shoots. You do this the same way you pinch zinnias.

Snip off central vines just above leaf joints and continue this throughout the growing season. The plant will be fuller, and, combined with deadheading (pinching off old flowers), will produce more flowers than it would if left unattended.

9Keep Soil Moist Not Damp—and Fertilize if Needed

Sweet peas don’t like to dry out: keep the soil consistently moist without allowing it to get soggy or dry. Super hot days can be brutal for these plants.

If you can’t tend to them daily, you might want to use slow-release water feeders or soaker hoses. I’ve got a list of self-watering garden options here.

Fertilizing is not necessary if the seeds are started or transplanted into a garden bed already amended with compost or composted manure.

If you do fertilize, keep in mind that it could trigger leafy growth but not flowers.

10Deadhead Flowers

Sweet pea flowers are fairly long-lasting but eventually they will begin to dry out and turn to seed. This starts when the summer heat becomes too much for them.

Deadheading is the process of trimming back the old flowers, which encourages new growth right into late summer or early fall.

To deadhead, find an old flower, follow the stalk down to a set of leaves, and trim just above the node (where the leaves meet the stem).

Taking cut flowers achieves the same thing: the plant is stimulated to continue growing rather than producing seeds (until the reduced sunlight and cool temperatures of fall win).

If you want to save seeds for next year, leave your best flowers on the plant. The best flowers provide the best seeds.

Frequently-Asked Questions

Summary

• Grow annual sweet peas. Beware of invasive perennial sweet peas.
• Sow seeds at the right time. Early spring is best. Fall is also possible in a heated greenhouse.
• Prep the seeds before sowing either by nicking the coat or soaking in moist paper towel or a cup of water (for up to 24 hours).
• Pick a morning sun growing location with rich soil and good drainage.
• Sow seeds at right depth (usually 1/2 to 1-inch). Plant at least 4-inches apart.
• Cover your newly-planted seeds with wire cloches to keep critters away.
• Add trellis early on for vines. And add twine or clips to help the plant climb.
• Pinch back main shoots if you want a fuller, bushier plant with more blooms.
• Keep soil evenly moist. Best to start with rich soil (compost, manure) rather than fertilizing.
• Deadhead flowers to extend blooming season.
• Save seeds from your best flowers for next year.

Resources

Video Growing Tips

Shop For Seeds

• Sweet Pea Seeds | Botanical Interests (US Shipping)
• Sweet Pea Seeds | West Coast Seeds (CAD Shipping)

There you go! You’re all set.

~Melissa the Empress of Dirt ♛