Snapdragons (Antirrhinum majus) are often treated as annuals, but they are actually short-lived perennials. In Zones 7 and above, they usually breeze through winter with zero help. However, if you live in Zones 4, 5, or 6, those sudden deep freezes can be a death sentence for these garden favorites.
If you have a particularly beautiful variety or want a massive head start on spring blooms, you can successfully overwinter them using two key techniques: heavy mulching and poly low tunnels.
Phase 1: Preparation (Late Autumn)
Before the ground freezes solid, you need to prepare the plants for dormancy.
- Don't Cut Back Too Hard: Leave about 4–6 inches of stem. This helps protect the crown of the plant.
- Clean the Base: Remove any fallen, diseased leaves to prevent fungal issues like rust from hibernating near the stems.
- Hydrate: Ensure the soil is moist before the first hard freeze. Dry roots are more susceptible to frost damage.
Phase 2: The Mulching Strategy
Mulch acts as a thermal blanket, preventing the "freeze-thaw" cycle that heaves plants out of the ground.
- Wait for the First Light Frost: This signals the plant to go dormant.
- Apply 4–6 Inches of Loose Mulch: Use pine straw, shredded leaves, or clean straw. Avoid heavy, wet wood chips that can pack down and cause rot.
- Mound the Crown: Ensure the mulch is tucked right up against the stems.
Phase 3: Building a Poly Low Tunnel
If you are in a zone where temperatures consistently drop below 10°F (-12°C), mulch alone might not be enough. A poly low tunnel creates a greenhouse microclimate.
Component Purpose
Support Hoops PVC pipes or heavy-gauge wire bent into "U" shapes over the row.
6-mil Greenhouse Plastic Traps solar heat during the day and blocks freezing winds.
Pro Tip: On sunny days in late winter, the temperature inside a tunnel can spike. If it gets above 45°F (7°C) inside, vent the ends of the tunnel to prevent the plants from "waking up" too early or rotting.
Spring Survival: The Wake-Up Call
Once the soil begins to thaw and the threat of extreme "deep freezes" has passed (usually 3–4 weeks before your last frost date):
Peel back the mulch: Gradually remove the heavy layers so the sun can warm the soil.
Fertilize: Give them a balanced, water-soluble fertilizer once you see new green growth.
Expect Early Blooms: Overwintered snapdragons usually bloom 3–6 weeks earlier than spring-sown seeds and produce much sturdier stems.
Anchor Pins/Sandbags To keep the plastic from flying away during winter storms.