Sweet peas can usually go outside in spring , once the worst of the cold and risk of frost have passed in your area, but the exact timing depends on your climate and how you raised them.

🔹 When to plant sweet peas outside

  • Indoor‑started seedlings:
    If you sowed seeds indoors or in rootrainers, plant them outside from late March to May , once they’re about 10–15 cm tall and there’s a mild spell with no hard frosts.
  • Direct‑sown outdoors:
    In milder climates (where the ground doesn’t freeze), you can sow sweet peas directly in the garden from late winter to early spring , as soon as the soil is workable and they’ll be fine with light frosts.
  • Very cold areas:
    In colder regions, gardeners often wait until late May , after the last frost, and harden off plants by putting them outdoors by day and bringing them in at night for about a week first.

🔹 Quick practical tips

  • Harden off: Set plants outside in a sheltered spot for a few hours each day, gradually increasing exposure over a week before leaving them out overnight.
  • Soil & sun: Choose a site with good drainage , full sun to light shade , and rich, moist soil; sweet peas thrive in cool‑ish spring weather and can struggle in very hot summers.

If you tell me your country or zone (for example “UK, zone 8” or “US zone 5”), I can give a more precise “safe” window for when your sweet peas can go outside.