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When to plant sweet peas: The best options for lots of fragrant flowers

Sweet peas are old fashioned annuals with ruffly, fragrant flowers in rich shades of blues, purples, reds, pinks, and whites.  They’re essential in cut flower and cottage gardens and for the best show of flowers, you’ll want to start the seeds at the right time. This article provides all the information you need to know about starting sweet peas seeds indoors as well as direct sowing in the garden. If you’re wondering when to plant sweet peas, keep reading. 

What are sweet peas?

Sweet peas (Lathyrus odoratus) are one of the most popular types of cut flowers and grown for their colorful and often richly scented blooms. Most sweet peas are vining annual plants that grow 6 to 8 feet tall and need the support of a trellis or other structure. That said, there are also compact sweet peas, like the dwarf variety ‘Knee Hi’, that have bushy growth. These are perfect for pots and hanging baskets. Antique varieties produce 3 to 5 pea-like flowers per stem, while choice varieties like ‘Spencer’, ‘Cutherberson’, and ‘Mammoth’ have been bred for long stems and extra-large blooms, with 5 to 6 flowers per stem.

Please note that unlike garden peas, sweet peas are not edible and all parts of the plant are poisonous.

2 options for when to plant sweet peas

Knowing when to plant sweet peas is the best way to encourage the healthiest and most productive plants. They’re tolerant of cool weather and unbothered by light frost. Your climate is the main factor for when to plant sweet peas and there are two options:

Option 1 – Autumn: In zones 8 and above, sweet pea seeds should be planted outdoors in autumn. They’re typically sown in October or November, about the same time spring-flowering bulbs are planted. You may not see a lot of plant growth in autumn, but the seeds are busy developing robust root systems and quickly sprout up when the weather warms in spring. Some gardeners in mild regions plant a second sowing in early spring to ensure the longest season of sweet pea flowers. 

Option 2 – Early spring: In cooler climates, zone 7 and lower, sweet peas are planted late winter through early spring. Seeds can be sown directly in the garden or started indoors. I start my sweet pea seeds indoors as transplanting seedlings results in more vigorous plants than those that are direct sown. Below you’ll learn more about when and how to start sweet peas seeds indoors as well as get tips on direct sowing in garden beds. 

When to plant sweet peas indoors

While you can direct sow sweet pea seeds, giving them a head start indoors under grow lights or in a sunny window gives the plants the strongest start. You’ll need to first figure out when to plant sweet peas indoors. To do this you need to know your last expected frost date. Sweet pea seedlings should be moved to the garden 2 to 3 weeks before the last frost date. So if my last average frost date is May 20th, I’ll be transplanting my sweet pea seedlings outdoors around May 1st. 

Ok, now I know when to transplant the seedlings in my garden, but when do the seeds need to be started inside? Next, we need to look at how many weeks of growth sweet peas need indoors before they’ve moved outside. They’re fairly quick to grow and should be sown indoors 4 to 6 weeks before you intend to transplant them to the garden. This means I need to count backwards 4 to 6 weeks from May 1st to determinate the indoor planting date. A quick glance at the calendar tells me I need to start my sweet pea seeds under my grow lights sometime between mid-March to early April. 

How to start sweet peas indoors

Now that we’ve figured out the timing, it’s important to know how to plant the seeds. Let’s look at the supplies you’ll need for starting sweet peas indoors.


  • 4 inch pots or cell packs placed in seeding trays
  • Seed starting growing mix
  • Plant labels and a waterproof marker
  • Grow lights or a sunny windowsill
  • Watering can

When you’re ready to plant, fill pots or cell packs with the pre-moistened growing medium. Sow the seeds 1/4 to 1/3 inch deep. Don’t bury the seeds too deeply or they may never germinate. Once planted, water the pots and move them under a grow light or place them in a sunny window. When the first seeds sprout, turn on the grow light, leaving it on for 16 hours a day.