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.
How to Grow Sweet Peas
Who doesn’t love sweet pea flowers? They are enchanting in the garden and have been a favorite flower for decades.
Have a look at the tips and don’t skip any if you want to ensure success. If you have struggled with germination, tip #3—preparing your seeds before sowing—should help.
10 Best Tips for Growing Sweet Peas
1Know What You’re Growing
Sweet Peas | Genus: Lathyrus
Sweet Peas | Genus: Lathyrus
Sweet Pea Growing Guide
Flowering plant or vine | Tips For Hardiness Zones 4-8
• Annual hardiness zones 7 up
• Perennial L. latifolius is invasive
• Sow seeds indoors 8-10 weeks before last frost and transplant after last frost or direct sow 6 weeks before last frost.
• Fall sowing is also possible in a heated greenhouse.
• Best Light: 6 hours morning sun
• Well-draining soil, rich in compost
• Do best in moderate summer temperatures, not heat
• Cut flowers: 4 to 5 days with preservative in vase water
• Seeds can be harvested for seed saving
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
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.
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.
Best Seed Sowing Temperature
The optimum soil temperature for sowing sweet pea seeds is
55-65°F (13-18°C) in spring.
You can measure your soil temperature using a kitchen thermometer. Measure at sowing depth and take measurements over several days to confirm a consistent temperature.
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.
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.
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.
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.
You can grow sweet peas in containers or hanging baskets but a bigger, in-ground growing space is usually better. The size of the flowers is proportionate to the size of the roots, and these plants like lots of room—both width and depth.
Containers at least 18-inches deep are recommended: a smaller size can inhibit growth. If this doesn’t matter to you, use smaller containers. They are beautiful flowers either way. Just be sure to keep up with your watering so they don’t dry out.
Some sweet pea seeds are marketed specifically for growing in containers so look for those.
Yes, sweet peas may self-seed in warmer climates. If you leave your sweet pea plants to turn to seed in fall and allow those seed pods to pop open and disperse the seeds, it is absolutely possible for some to self-seed next year. We know this happens in zone 7 or warmer. It could also happen in colder climates if the seed does not freeze during the winter.
Sweet peas will grow more abundantly with pinching back (selectively removing the tips of main stems) and deadheading (removing dead flowers and their stems) but it’s totally optional.
To grow sweet pea on a trellis or arch, be sure to install the supports at planting time. Adding trellis later risks damaging the plants. Check the plants every few days to be sure the tendrils are grabbing the supports and covering the trellis nicely.
Yes, you can save sweet pea seeds for future sowing. When the flowers are done blooming pods will form. These pods will grow seeds inside. They are ready for harvesting when they are brown and dry and the pods are just starting to pop open.
If conditions are right, the saved seeds should be viable for 3-5 years.
Yes, sweet peas make lovely cut flowers. The trick is to pick your sweet peas when the flowers at the top of the stem have not yet opened. Make a good, clean cut on the stem. Place the cut flower directly in a vase of room temperature water with cut flower preservative. They generally last 4 to 5 days in a vase.
- 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.
Video Growing Tips
Shop For Seeds
- Sweet Pea Seeds | Botanical Interests (US Shipping)
- Sweet Pea Seeds | West Coast Seeds (CAD Shipping)
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