Growing sweet peas from seed is a great place to start if you’re looking for an easy and rewarding gardening project. These beautiful flowers come in a wide range of colors and have a sweet fragrance that will brighten up any garden.
Sweet peas are easy to grow from seed and can be started indoors or directly in the garden. The best time to plant is during the cool weather of early spring or fall for overwintering. Rich soil and a sturdy trellis will produce tall plants that bloom profusely all season.
In this article, I’ll show you how to grow sweet peas from seed, including tips on direct sowing and starting your seeds indoors.
By the end of this guide, you’ll have everything you need to know to get started on your own sweet pea garden.
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When to start sweet pea seeds
Fall or late winter are all great times to start sweet peas from seed. Even early spring is an option if you choose a heat-tolerant variety. Basically, avoid the heat of summer.
Sweet peas grow best in cooler temperatures, so starting them sometime in the fall or winter will give them a chance to develop a strong root system before focusing on flower production.
If you live in a mild climate, try fall sowing your sweet peas in September or October. They’ll sprout and grow up until the days get too short, usually around November. Then, the plants will sit dormant until late winter when the days start to lengthen.
If you have harsh winters or you’re getting started in the winter, sow your seeds about a month before your last frost date. It might take the seeds a little while to germinate, but be patient, and they’ll poke through the soil eventually.
Once you have your timing figured out, it’s time to choose the right location for your sweet peas. These flowers prefer a sunny spot with well-draining soil. Make sure the spot you choose gets at least 6 hours of sunlight each day and that the soil is rich and fertile.
Containers are another option if you don’t have access to garden space or if your soil needs work before it’s ready to plant. Choose a pot that’s at least 12 inches wide and tall, so there’s room for the roots.
I’ve had good results with planting dwarf sweet peas in hanging baskets, as well, especially with the Sugar ‘n Spice variety.
How to start sweet peas from seed
Choose from direct sowing in the garden or starting seeds indoors. Both methods are easy, and despite what some say, sweet peas transplant easily without damaging their roots. Have gentle hands, of course, and give it a try for earlier flowers.
Before planting sweet pea seeds, you can soak them overnight to speed up the germination process. The soaking softens the hard outer coating, making it easier for the seed to crack open.
Direct sowing in the garden or pots
Once soaked, it’s time to sow the seeds in the soil. Using a trowel, dig a series of holes that are about 1 inch deep and 3 inches apart and place 1-2 seeds inside. Alternatively, make a furrow in the soil and sprinkle the seeds down the length of it with one seed every couple of inches.
This method is perfect for sowing at the base of a long trellis, whereas individual holes are great for sowing at the feet of a teepee or triangular obelisk.
Cover the holes or furrow with soil and lightly pat it down. Water lightly over the area to settle the seeds and dirt, and wait for germination. You can lightly mulch at this point or wait for the seeds to sprout, then mulch around them.
Starting sweet peas indoors
While you can plant sweet pea seeds directly in the garden, starting them from seed indoors can give you a head start on the growing season.
This is particularly useful if you live in a colder climate or if you want to enjoy sweet pea blooms earlier in the season.
To plant sweet peas indoors, gather up your seed-starting equipment, including seed trays or pots, a seed-starting mix, and grow lights or a sunny windowsill. You will also need to time the planting so that your seedlings are ready to transplant into the garden once the weather warms up.
Begin by filling your seed trays or pots with a high-quality seed-starting mix. Moisten the soil lightly and then plant the sweet pea seeds about an inch deep. Put 1-2 seeds per cell or pot if using 6-packs.
Cover the seeds with soil and then place the trays or pots in a spot where you can check on them to monitor the soil moisture. They don’t need any grow lights until they’ve sprouted.
Keep the soil moist but not too wet, and once the seeds have germinated, make sure that the seedlings get plenty of light. In a pinch, you can use a sunny window, but cheap shop lights are really better here and will result in much stronger plants.
Once the seedlings have grown to about 3 inches tall, you can begin to harden them off by gradually exposing them to the outdoor environment.
You can read exactly how to harden off your plants here (and avoid killing your seedlings!): 7 Ways To Minimize Transplant Shock In Seedlings.
You can transplant your sweet pea seedlings up to a month before the last frost if they’re properly hardened off. Sweet pea plants are relatively cold tolerant, though they probably won’t survive being covered in snow for long, so time your planting according to your local weather.
Space the seedlings 3-4 inches apart and leave room to install a trellis. You can put up the trellis before transplanting, too, and make it simple to start training the vines up right from the start.
Here are some ideas for sweet pea trellises in this article: Should I Trellis Sweet Peas? (Tips For Success).
Overwintering sweet peas
If you want to get the earliest flowers, think about fall sowing your sweet peas to overwinter them. Instead of sowing the seeds in early spring, you’ll sow the seeds in fall along with your other fall crops, like kale, lettuce, and carrots.
Sweet peas don’t mind a bit of cold weather, but they can’t take heavy snow loads or repeated freezes and thaws, so here are two ways to sow in the fall and provide some protection:
Direct sow and cover
With this method, you’ll plant the sweet peas where you intend to grow them next year, probably around September or October. By the time your first fall frost rolls around, you’ll want to have some sort of season extension in place, whether that’s a low tunnel, a pop-up greenhouse, or a row cover.
The protection will keep the temperatures just a little warmer to prevent the plants from freezing. Monitor them over the winter and remove them in the spring once the weather starts to warm up.
Sow in pots for transplanting
Another way to start fall sweet peas is to sow them in root trainer pots, which are long and narrow pots that have plenty of room for peas’ long taproot. Just like direct sowing, you’ll want to sow the seeds in September or October.
Once the weather turns cold for the winter, put the pots in a sheltered area like under the eaves, in a greenhouse, or in a coldframe. In the spring, typically around March, you can plant the seedlings out in their permanent location and you’ll have sweet blooms in no time.
Caring for your growing sweet peas
Tending your sweet peas is pretty hands-off once they’re established.
They will need regular watering if you’re having a dry spring. Once or twice per week should be plenty, totaling about an inch of water per week.
You can fertilize throughout the blooming period with a balanced fertilizer, but if you start with a rich soil that has compost mixed in, you probably won’t need to add any extra fertilizer.
As small plants, your sweet peas might need some help to get started on their trellis. You can weave the tendrils into the trellis, and the vine will quickly catch on and take over the job.
Most varieties will reach 4-5 before they start producing flower buds, then continue climbing to six feet or so as they flower.
Overall, caring for sweet pea plants is a relatively easy process. Just be sure to water regularly and provide support as needed. With just these two things, your sweet pea plants will reward you with beautifully scented blooms all season long.
Don’t forget to cut some stems for a pretty little bouquet! Sweet pea steps will last about a week in the vase if you pick them young and keep the water clean.
Once the heat of July and August hit, your plants will likely produce fewer flowers. The leaves will eventually yellow and you’ll see seed pods forming as the sweet pea flowers shrivel.
If you want to try saving the seeds, allow a few pods to dry on the stems and harvest them just before the pods burst. Store the seeds in a paper bag and you’ll have a supply of fresh seeds for next season.