Unlike annual plants that complete their lifecycle in one growing season, perennials and shrubs are designed to survive through winter. However, when grown in containers, their roots are more vulnerable to freezing temperatures. Let’s explore how to properly overwinter your potted perennials and shrubs to ensure their survival and health for the next growing season.
Why Overwintering in Containers is Different
When plants grow in the ground, the surrounding soil insulates their roots, keeping them warmer than the air temperature during winter. In contrast, container-grown plants lack this natural insulation. Pots tend to freeze and thaw rapidly, which can stress or even kill plants. This makes it essential to take extra precautions.
General Rule for Winter Hardiness in Containers
A good rule of thumb is to select plants that are hardy to at least two zones lower than your local USDA hardiness zone. For instance, if you live in zone 6, choose plants that are hardy to zone 4 or lower for better chances of success. While it’s possible to grow less-hardy plants, you’ll need to follow additional steps to protect them.
Five Tips to Successfully Overwinter Plants in Pots
1. Choose the Right Containers
The type of container you use plays a significant role in protecting your plants during winter. Certain materials, such as clay, ceramic, and glazed pots, are prone to cracking in freezing temperatures. This not only damages the container but also exposes the plant’s roots to cold air and drying winds.
For best results, opt for durable materials like plastic, wood, or composite pots that are designed to withstand freezing and thawing cycles. Avoid leaving your plants in thin nursery pots, as they offer little to no insulation against the cold.
2. Relocate Your Pots to a Sheltered Area
Leaving planters exposed to harsh winter conditions can be risky. Instead, move them to a protected location such as:
- Against the wall of your house or shed.
- Under a deck or similar structure.
- Inside an unheated garage or shed.
Important: Avoid bringing your pots indoors to heated spaces. Most perennials and shrubs require a period of dormancy in cold temperatures to thrive in the next growing season. Moving them to a warm environment can disrupt this natural cycle and may even harm the plants.
Tip: Wait until temperatures drop consistently below freezing and the plants are nearly dormant before moving them to a sheltered spot.
3. Use Insulation to Protect Roots
If relocating your pots isn’t an option, you can insulate them where they are. Wrap the containers with materials such as:
- Burlap.
- Blankets or old towels.
- Thick bubble wrap.
For additional protection, you can bury the pots in the ground up to the base of the plant. This mimics the natural insulation that soil provides to in-ground plants. Finish by adding a layer of mulch to the top of the soil in the container, which helps retain moisture and adds an extra layer of insulation.
4. Water Sparingly but Consistently
Dormant plants still need water, but overwatering can be harmful. Keep the soil lightly moist throughout winter to prevent roots from drying out. Check the soil every few weeks by inserting your finger to feel the moisture level. If it’s dry, water lightly. If it’s still moist, hold off on watering.
Plants left in uncovered areas often receive sufficient water from winter precipitation. However, pots in sheltered spots, such as under a roof, will require occasional watering.
5. Avoid Fertilizing and Pruning
Winter is not the time to fertilize or prune your plants. Fertilizing in late summer or fall can encourage new growth, which is highly susceptible to cold damage. Pruning too late in the season has a similar effect.
Instead, let your plants naturally enter dormancy. Reserve fertilization and pruning for the early spring when growth resumes, ensuring your plants are prepared to flourish in the warmer months ahead.
Final Thoughts on Overwintering Success
Overwintering perennials and shrubs in containers requires thoughtful preparation and care. By choosing the right pots, relocating them to sheltered areas, insulating effectively, maintaining proper moisture levels, and avoiding untimely fertilization or pruning, you can protect your plants from harsh winter conditions. With these steps, your plants will emerge healthy and ready to thrive in the upcoming growing season.
