3 Tips to Prepare Your Garden for Cold Weather
By Ray Daugherty
1/13/2025
Temperatures may dip below freezing this weekend. To prepare, Ray Daugherty, West Seattle Nursery’s Shrub Buyer, highlights the importance of understanding your plant’s USDA hardiness zone, tips for protecting vulnerable plants, and caring for cold-damaged plants to help them thrive again in spring.
Know your plant’s “USDA hardiness zone”
The USDA divides the United States into 13 hardiness zones. Each zone represents a 10-degree Fahrenheit difference in average minimum air temperature. Larger values indicate more mild conditions whereas smaller values indicate colder temperatures. So, gardeners in zone 6 would expect temperatures between 0 and -10 degrees Fahrenheit to occur each year. On the other hand, gardeners in zone 9 would never expect temperatures to drop below 20 degree Fahrenheit in an average year. The current USDA zone map places Seattle in zone 9 (20-30F). As experienced gardeners though we would remind you that temperatures in frost pockets may drop to as low as 10F during cold snaps; making Seattle functionally USDA Zone 7 or 8. This means that if a plant in your garden is rated as USDA Zone 8 or 9 it may be damaged during cold weather and should be your first concern as very cold weather approaches.
Remember, too, that zone maps are based on air temperature. Garden plants normally grow in large masses of soil that protect their roots from rapid temperature fluctuations, essentially insulating them during cold snaps. Container-grown plants, on the other hand, are fully exposed, and their roots experience temperatures 5 to 10 degrees Fahrenheit colder than they would in the ground. This means container-grown plants should be considered one zone less hardy than they would be in a garden. Even Zone 7 plants may be damaged by a cold snap when grown in pots. To protect them from the cold, potted plants can be grouped together, or insulation can be placed around them to help retain the soil's heat, lessening the damage they might experience.
Don’t forget to water if the plant is dry
Yes, we live in rainy Seattle. But plants in rain shadows (usually pots under a porch roof or awning) may still dry out during the winter. During cold a cold snap, even slightly dry plants lose stems to dehydration (freeze drying). To avoid this, irrigating 24 to 72 ahead of cold weather will help avoid damage.
Pay attention to plants that were nutrient starved or struggling
Sugars and mineral nutrients in the plant’s cells act as antifreeze; allowing the plant to survive cold weather. If a plant was growing poorly in the fall, it is likely it was a bit starved for nutrients and therefore may have low sugar levels in its cell. If it survives the freeze, consider giving better growing conditions next year. This may mean giving it a bit more sun and a dose of fertilizer (once spring growth resumes!).
If cold damage does occur, the best response is to take a wait and see attitude. Don’t kill it with kindness. Let it dry down between watering – just like you would normally! Don’t fertilize until new growth returns. Prune to remove obviously dead twigs. Prune out questionable twigs only when new growth allows you to see the true extent of the damage.
For additional tips, check out our blog post: 4 Products to prepare your garden for a freeze!
