Sweet peas (Lathyrus odoratus) are annual flowering plants prized for their fragrant, colorful blooms. While they thrive in cool weather, their tolerance to frost varies depending on their growth stage and environmental conditions. Young sweet pea seedlings are more susceptible to frost damage, whereas established plants may withstand light frosts (temperatures slightly below freezing) for short periods. However, prolonged exposure to hard frosts (below 28°F or -2°C) can be fatal.
Frost affects sweet peas at a cellular level. Ice crystals form within plant tissues, rupturing cell walls and disrupting water transport. Symptoms include wilting, blackened foliage, and stunted growth. While mature sweet peas may recover from mild frost, repeated exposure weakens the plant, reducing flowering potential. In contrast, seedlings often die if unprotected, as their tender stems and leaves lack resilience.
To enhance frost survival, consider these strategies:
a. Timing: Sow seeds in late winter or early spring after the last frost date in your region. In mild climates, fall planting is possible with protection.
b. Mulching: Apply a 2–3 inch layer of straw or compost around the base to insulate roots and retain soil warmth.
c. Covering Plants: Use frost cloths, row covers, or even old bedsheets to shield plants overnight. Remove covers during the day to prevent overheating.
d. Microclimates: Plant sweet peas near south-facing walls or under tree canopies to exploit radiant heat and wind protection.
Sweet pea survival depends on local climate zones:
a. Mild Winters (Zones 7–10): Plants may survive outdoors with minimal protection. Mulching and occasional covering suffice.
b. Moderate Winters (Zones 5–6): Heavy mulching and frost cloths are essential. Consider planting in containers that can be moved indoors during extreme cold.
c. Harsh Winters (Zones 3–4): Sweet peas are unlikely to survive frost without greenhouse or indoor overwintering. Treat as annuals or start seeds indoors for early spring transplanting.
If frost damages sweet peas, assess the extent:
a. Minor Damage: Trim blackened foliage and water lightly to encourage new growth. Avoid fertilizing until active growth resumes.
b. Severe Damage: Replace plants if roots are mushy or stems are entirely collapsed. Resow seeds if the growing season allows.
c. Preventive Monitoring: Watch for fungal diseases like powdery mildew, which thrive in cold, damp conditions. Improve air circulation and avoid overhead watering.
In regions with harsh winters, treat sweet peas as annuals. Sow seeds early indoors (6–8 weeks before the last frost) and transplant outdoors after temperatures stabilize. This ensures blooms before summer heat, which often causes sweet peas to decline.
