Yes, you can keep soil in pots over winter, but it requires some planning to protect your plants and the containers themselves. Winterizing your potted plants is a crucial autumn task that prevents cracked pots, frozen roots, and disappointing losses come spring. With the right steps, you can successfully tuck your container garden in for a cold season.
The main challenges are freezing temperatures and excess moisture. When soil in a pot freezes, it expands. This can shatter clay, ceramic, and even some plastic pots. For plants, frozen roots can’t take up water, leading to desiccation and death, even if the plant is technically hardy. Your goal is to moderate these extremes.
Can You Keep Soil in Pots Over Winter
The direct answer is a qualified yes. You can leave soil in pots over winter, but you must decide whether you’re protecting a perennial plant in that soil or simply storing the empty pot and soil for reuse. The strategies differ slightly, but both focus on insulation and drainage.
Why Pots Are Vulnerable in Winter
In the ground, plant roots are insulated by the immense thermal mass of the earth. The soil temperature a few inches down remains relatively stable. A pot, however, is an isolated chunk of soil exposed to air on all sides. It freezes quickly and thoroughly, subjecting roots to the same temperature as the air. This is why a plant that’s hardy in your zone in the ground may not survive in a pot.
Additionally, winter sun and wind can dry out above-ground foliage while the roots are locked in frozen soil, unable to replace lost moisture. This causes “winter burn.” Constant freeze-thaw cycles are also destructive, heaving plants and soil up and breaking roots.
Step-by-Step: Winterizing Potted Perennials, Shrubs, and Trees
This process is for plants that will stay in their pots, like hardy herbs, ornamental grasses, roses, shrubs, and small trees.
1. Know Your Plant’s Hardiness. Check its USDA hardiness zone. If your local winter is more than one zone colder than the plant’s rating, it will need extra help or should be brought indoors if possible.
2. Stop Fertilizing. By late summer, stop feeding your plants. You want to discourage tender new growth that will be killed by frost.
3. Water Deeply Before the Freeze. Well-hydrated soil freezes more slowly and provides moisture for the plant through winter. Give a thorough soaking before the ground solidifies.
4. Clean Up and Trim. Remove all dead leaves and spent annuals from the soil surface to prevent disease. Do not do major pruning in fall; save that for spring.
5. Protect the Pot. This is critical. Group all pots together in a sheltered location, like against a house wall or in an unheated garage. Then, insulate the container.
* Bury the Pot: The best method. Sink the pot into a vacant garden bed, covering the rim with soil.
* Create a Mound: Pile mulch, leaves, straw, or wood chips around and over the pot to cover the soil and sides.
* Wrap the Pot: Bubble wrap, burlap, or special pot blankets work well. Secure it with twine.
6. Protect the Plant. For the top growth, use burlap screens to shield from wind or construct a simple frame around the plant filled with dry leaves.
Storing Empty Pots and Soil Over Winter
If your pots held annuals or you’ve moved tender plants inside, you can store the pots and soil together. This saves time and money in spring.
1. Remove Plant Debris. Pull out all old roots and stems to prevent rot and pests.
2. Let it Dry Slightly. Don’t store sopping wet soil, but don’t let it bake bone-dry either. A slightly moist state is ideal.
3. Stack and Store. You can stack pots with the soil still in them. Place them in a shed, garage, or against a sheltered wall. If stacking, put the emptiest pot on the bottom.
4. Cover the Top. Use a piece of wood, a tray, or even plastic to keep excess rain and snow from waterlogging the soil. This prevents nutrient leaching.
When to Replace Potting Soil Instead
You shouldn’t reuse soil indefinitely. Replace it if:
* The plants that were in it showed signs of disease.
* It’s become very hard, compacted, or won’t absorb water.
* It’s been used for several growing seasons and is likely depleted of nutrients.
* You notice a white crust on the surface, which indicates harmful salt buildup.
Old soil can be added to your compost pile or used as a filler in the bottom of very large containers.
Special Cases: Tender Bulbs and Sensitive Plants
For plants like dahlias, cannas, or tropical specimens, the pot-and-soil method is perfect for storage.
1. After frost blackens the foliage, cut it back.
2. Let the pot dry out completely in a garage or basement for a week or two.
3. Store the entire pot, dry soil and all, in a cool, dark place where temperatures stay between 40-50°F (4-10°C).
4. Do not water at all during dormancy. In spring, bring the pot to light and warmth, and begin watering to wake the plant up.
Common Mistakes to Avoid
* Letting Pots Sit on Saucers: This traps water and guarantees frozen roots. Elevate pots on “pot feet” or bricks for drainage.
* Using Plastic Wrap Directly on Soil: This creates a suffocating, mold-friendly environment. Use breathable materials like burlap.
* Overwatering in Fall: Soggy soil is colder and more likely to freeze solid and cause root rot. Water deeply once, then let nature take over.
* Forgetting About Rodents: Cozy, insulated pots are attractive to mice and voles. Avoid using grass clippings or dense hay for mulch, and consider deterrents if they’re a problem in your area.
Spring Awakening: What to Do When Warm Weather Returns
Don’t rush to uncover your plants. As temperatures slowly rise in spring:
1. Gradually remove insulating wraps and mulch as the risk of hard frost passes.
2. Begin watering carefully if the weather is dry.
3. Wait for new growth to appear before applying any fertilizer.
4. Gently check for root health and repot if the plant has outgrown its container.
FAQ: Winterizing Your Potted Plants
Q: Can I leave my plastic pots outside in winter?
A: Yes, but they can become brittle and crack in extreme cold, especially if the soil inside freezes. It’s still best to insulate them or move them to a sheltered spot.
Q: Should I water my potted plants in winter?
A: For dormant hardy plants, only water during an extended winter thaw if the soil is very dry. For plants in unheated shelters, check monthly and water lightly if the soil is dust-dry.
Q: What is the best mulch for insulating pots?
A: Shredded leaves, straw, or wood chips are excellent. They provide air pockets for insulation without compacting to much.
Q: Can I winterize my potted plants in an unheated garage?
A: Absolutely. An unheated garage is an ideal location. It provides shelter from wind and the worst cold, but remember to water occasionally as the soil will dry out.
Q: Do I need to protect concrete or fiberglass pots?
A: Concrete can crack from freeze-thaw cycles, so insulating it is wise. Fiberglass is generally very resilient, but the plant inside still needs protection from root-freezing.
Successfully keeping soil in pots over winter boils down to managing temperature and moisture. By providing insulation, ensuring drainage, and choosing the right strategy for each plant, you can protect your investment and enjoy a thriving container garden year after year. A little effort this fall saves you from the cost and dissapointment of replacing plants and pots every spring. Start your winterizing plans before the first hard frost arrives for the best results. Your future self will thank you when you see those first green buds pushing through next season.