When to Plant Sweet Peas: Tips For Your Zone
Sweet peas are a beautiful addition to the early spring garden and make wonderful spring arrangements. Join cut flower gardener Melissa Strauss to discuss when you should plant them in your zone and how to do it.
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Sweet peas are a delightful addition to the spring garden. They will cover a trellis with delicate vines and fragrant blossoms, and they are excellent as cut flowers. Getting them started isn’t difficult, but there are some important factors to take into account.
These pretty plants are cool weather lovers. In fact, they are surprisingly cold-tolerant. Young plants will tolerate temperatures in the low 20s (~-7°C) before they need covering. This makes it easy to plant them ahead of time and get them growing well before the weather heats up.
Sweet peas do not like warm weather. They are one of the more heat-sensitive plants I can grow here in my North Florida yard. That means that the earlier I can plant them, the longer I will have to enjoy them.
Planting time for sweet peas will vary, as with most seeds, according to your climate. The warmer the climate, the sooner they will need to go in the ground if you want to see plenty of beautiful blooms.
Zones 8 and Higher
Because of the brevity of the cool season in these warmer zones, growing these vines can be a challenge. They need cool weather to establish strong roots, and they are sensitive to hot weather. When the temperature consistently rises above 80°F (27°C), they will stop producing and begin to wither.
Fortunately, they have excellent cold tolerance. In zone 9, where I live, it rarely drops into the 20s (-7°C). When it does, it only happens at night and doesn’t typically last more than a few days. Since these are tolerant of temperatures down to the low 20s, this means that we can start them extra early.
The ideal time to start your seeds in warm climates is in mid-fall, between September and November should be just right. You can get going as soon as the weather begins to cool off, and it’s unlikely to get hot again. You can start your seeds indoors, but I recommend directly sowing them if you’re able. They transplant fairly but will be more robust if you don’t move them around.
Zones 5, 6, and 7
January is the best time to start your seeds for mid-range zones where the ground freezes, but the summers are hot. If you can’t work the soil, start them indoors and then plant them out about eight weeks ahead of your last anticipated frost date.
Remember that these plants don’t just tolerate cold weather. They prefer it. Their roots develop better in cool soil and stop growing at about 80°F (27°C). You want to have them well on their way by that last frost date. If you start your seeds in trays, make sure that you keep them in a cool spot. Growing them warm will result in fast, leggy growth, not full, bushy plants.
Zones 3 and 4
For those cool climate areas, you can grow these well into the summer months. They will be happy if your soil temperature stays below 80°F (27°C). If you want to start them early, you can do so and then transplant them when the soil is workable.
Since you have a cooler summer in these areas, it’s fine to wait until the soil is workable and plant these in early spring. No need to worry about your last frost date; the seedlings appreciate some freezing weather. As long as it doesn’t drop below their cold hardiness, they will be perfectly fine.
In these zones, I would directly sow my seeds as early as possible. Again, don’t worry as much about that last frost date as whether your soil is solid.
How to Do It
Sweet peas prefer to stay in one place, so directly sowing them is always the best option if possible. If you need to start them indoors because of temperature difficulties, it’s ok, you can transplant them, but it’s just not the ideal method.
These seeds have a hard outer shell. Often, seeds with this coating benefit from some preparation before you plant them. Sweet peas fit into this category. Gently scarify them with a file or fine-grit sandpaper and then soak them.
Soak for up to 24 hours before sowing them. This will help to soften the outer shell, and allow water in to set the germination process in motion. Plant three to a hole, about one inch deep and six inches apart. Thin them out to one every six inches once they reach three inches tall.
If you prefer to start these indoors, using biodegradable pots is best. This way, you don’t have to disturb the roots. Start them about four to six weeks ahead of your last frost date, and transplant them when they are about four to six inches tall.
After planting and establishment, sweet peas benefit from pinching when they reach about six inches tall. Pinching them encourages branching, so you’ll have nice, bushy plants that produce an abundance of flowers. The more branching, the better the bloom will be. I pinch again when they are about nine inches to a foot tall to encourage them to branch again.
Sweet peas are climbing or trailing vines, so make sure to give them a trellis or other support to climb. You can also plant smaller types in hanging baskets. Deadheading is important to keep your plants blooming as long as possible. If you leave flowers on the vines, they will go to seed and shorten the life of the plant.
Soil
In terms of soil, these vines grow best in well-drained, fertile soil. The pH should be between 6.0 and 7.5, so right around the neutral mark. If you have dense soil, amend it with organic matter like compost or manure and perlite to improve drainage.
Sun
Sweet peas prefer full sun, at least six hours per day. They need as much sun as you can give them in cooler regions. In warmer climates, planting them in a position where their roots have some shelter will prolong their life. Keeping those roots cool is the key to a long growing season.
Water
These are moisture-loving plants, and their need for moisture increases with the temperature. Keep the soil cool and moist as much as possible. In the ground, you’ll want to water them two to three times per week. I grow mine in a raised bed, so the soil drains quickly and dries out faster. As the summer draws nearer, I will water them daily to keep them hydrated and cool.
Fertilizer
Sweet peas are nitrogen fixing, so they don’t need much in the way of supplemental nitrogen. A light dusting of bone meal at planting will give them a boost. A bloom-boosting fertilizer applied at the same time will also help them along. These usually contain higher concentrations of potassium and phosphorus.
