Quick Answer
Potting soil can be left outside over winter, but there are some precautions you should take to protect it. Covering the soil with a tarp, storing it off the ground, and keeping it dry are some tips for proper winter storage. Unprotected potting soil may become saturated, freeze, thaw and become moldy if left outdoors exposed to the elements all winter.
Should You Leave Potting Soil Outside in Cold Weather?
Potting soil is typically a mixture of peat moss, compost, perlite or vermiculite that provides nutrients and drainage for container gardening and houseplants. While potting mix contains organic materials that can break down over time, it’s best not leave bags of unused soil exposed to outdoor conditions for extended periods.
Freezing and thawing cycles, excessive moisture and pests can damage potting soil quality if it is left outside through the winter. However, you can safely store potting soil outside over winter if you take some basic precautions.
Here are some tips for properly storing potting soil outdoors when the weather turns cold:
– Keep it covered: Put a waterproof tarp or plastic sheeting over stacks or pallets of potting soil bags. This will protect the soil from becoming waterlogged from rain, snow and ice.
– Store off the ground: Place pallets, boards or bricks under bagged soil to keep it elevated off the ground. This allows for air circulation and prevents the bottom layer of bags from getting wet.
– Check for water: Periodically check under the tarp to make sure no water has pooled on the bags. Drain or soak up excess water to keep soil bags from getting heavy and rotten.
– Keep it dry: Store in a shed, garage or carport to keep potting mix sheltered from moisture. Make sure the storage area has adequate ventilation to prevent dampness.
– Protect from pests: Keeping soil off the ground and covered deters mice, insects and snakes from nesting in it over the winter months.
– Use pallets: Stack bags on pallets to make moving and storing the heavy soil easier, while keeping it off the ground.
– Store indoors: For best results, bring unused soil indoors to a basement, garage or shed. This prevents damage from changing weather conditions outdoors.
What Happens if Potting Soil Gets Too Wet?
Leaving potting soil outside exposed to rain, snow and ground moisture can cause a few issues:
– Saturation: Potting mix left uncovered will become waterlogged from precipitation. Excessive moisture causes nutrients to leach out.
– Freezing: Saturated soil left outside in freezing temperatures will become frozen solid. As it alternately thaws and re-freezes, this expansion damages soil structure.
– Mold growth: Wet potting mix promotes mold growth. Gray fuzzy mold can rapidly spread through bags of soil left wet for long periods. This makes potting soil unhealthy for plants.
– Pest infestations: Wet, rotting organic matter attracts unwanted pests. Bugs, frogs and mice may find a home in soil bags that contain a lot of peat moss.
– Foul odors: Anaerobic bacteria thrive in waterlogged soil, producing sulfur and ammonia gases that create strong rotten smells.
To avoid these issues, check potting soil often and cover, drain or move it somewhere dry if the bags feel heavy with moisture. Discard any bags with visible mold or pests. Let overly wet soil dry out before using.
Can You Store Potting Mix Outside in a Bag?
Unused potting soil can be kept successfully in its original plastic bags outside over the winter by following best practices:
– Elevate bags – Place potting soil up on pallets or cinder blocks to prevent contact with wet ground and allow airflow beneath bags.
– Use a tarp – Cover the pallet stacks with an impermeable tarp or sheet secured on all sides to keep rain and snow off the bags.
– Check for moisture – Inspect under the tarp periodically and pour off any collected water before it can seep into bags.
– Ventilate – Make sure the tarp is not sealed tight to the ground so air can circulate to prevent condensation under the tarp.
– Add supports – Place wood planks or another pallet underneath to support bags from sagging or breaking on the bottom.
– Store high traffic areas – Keep potting soil in a spot like a covered driveway or near a doorway where you will walk by and notice any issues.
– Bring delicate bags indoors – Any torn or flimsy bags should be stored somewhere dry like a garage or shed protected from the elements.
With the right precautions, potting mix bagged by the manufacturer can successfully be left outside for the duration of winter and be ready for use come spring. Just be diligent about checking for and preventing excess moisture.
Should You Cover Extra Potting Soil for the Winter?
Leaving unused, leftover potting soil outside uncovered all winter is risky. It’s best to provide some sort of cover to protect it from precipitation and pests until needed. Here are some good options for covering stored potting mix:
– Plastic tarp – An inexpensive plastic tarp is very effective for keeping soil dry. Choose a thick 4-6 mil tarp and weigh down the edges with bricks or stones.
– Canvas tarp – More durable than plastic, canvas tarps allow airflow to prevent condensation. Waterproofed canvas resists mold and mildew better.
– Greenhouse plastic – Clear 3-year greenhouse plastic lets in sunlight yet repels water. It traps heat while allowing ventilation along the edges.
– Fiberglass panels – Lightweight, rigid corrugated fiberglass panels shed water well. They allow more light and air circulation than solid tarps.
– Wood panels – Protects from rain and snow while allowing airflow, but can be heavy and deteriorate over time. Elevate off the ground.
– Concrete paving stones – Overlapping solid concrete pavers provide a waterproof, breathable cover that allows for airflow when stacked.
Any covering that shields potting soil from the elements while still allowing for some ventilation and drainage will work. Just check periodically for any leaks, gaps or tears that could expose the soil.
Can Potting Soil Be Stored Outside Without a Bag?
Loose potting soil that isn’t contained in a bag requires more protection when stored outside for the winter. A plastic tarp alone won’t contain unbagged soil in windy conditions. Here are some better options:
– Covered trash can – A lidded 32-64 gallon plastic garbage can with drainage holes drilled in the bottom keeps soil contained and allows excess moisture to drain out.
– Wooden box – A homemade plywood box with a waterproof liner stores multiple cubic feet of loose potting mix neatly while keeping it covered.
– Wheelbarrow or cart – Lining a wheelbarrow or garden cart with a tarp or plastic bag creates a mobile covered container for loose soil that can be moved under cover.
– Children’s plastic pool – An inexpensive kiddie pool, sand box or plastic storage tote can hold and protect a few bags of loose soil when flipped upside down over the pile.
– Concrete block bin – Concrete cinder blocks or bricks stacked into a three-sided bin will securely corral loose potting soil while still allowing for airflow and drainage.
Any container that keeps the soil restrained, separated from the soil beneath and protected from heavy rain or snow will work. Just ensure it has ventilation so condensation doesn’t accumulate. Check soil moisture levels before use in spring.
Can you Store Potting Mix Directly on the Ground Over Winter?
It’s best not to leave extra potting soil directly on the bare ground over winter if possible. Contact with the soil beneath can compromise potting mix quality and lead to issues like:
– Waterlogging: Ground moisture can be wicked up into potting soil from below, saturating it.
– Nutrient leaching: Minerals and fertilizers will leach down into surrounding native soil over time when in direct contact.
– Weed seeds: Storing directly on soil can introduce weed seeds that will sprout when potting soil is used in spring.
– Pest contamination: Bugs, worms and rodents from the ground can make their way up into unprotected potting soil.
– Hardening: Bagged soil left on the ground can harden into a solid mass that’s difficult to break up come spring.
– Wasted product: The bottom layer of soil may become too compacted, damp or contaminated for use.
For best quality and to avoid waste, store potting mix up on pallets or pavement if possible. Or use a waterproof tarp, container or plastic sheet as a barrier between the soil and bare earth beneath. Check for weed seedlings or signs of pests before using potting soil stored on the ground.
Keeping Potting Soil Dry Over Winter
Since excess moisture is the biggest threat to potting soil stored through winter, here are some tips to keep it dry:
– Check soil moisture every 1-2 weeks using your fingers. It should feel lightly damp, but not soggy wet.
– Create drainage by elevating soil on pallets or shelves.
– Use a breathable waterproof cover like a tarp or canvas. Avoid solid plastic sheeting.
– Store in an open shed or garage rather than fully enclosed space.
– Place soil in an area protected from groundwater, puddles and downspouts.
– Discard any overly wet or moldy bags.
– Turn bags periodically to dry all sides.
– Add more aeration by remixing in perlite, vermiculite, bark or coconut coir.
– Stir in gypsum to improve drainage and draw moisture out.
With a little diligence, you can keep potting soil in good shape over the winter months. Just try to maintain moderate moisture levels andproper air circulation until ready to use.
Conclusion
Potting soil can be left outside over the winter without problems as long as you take some basic precautions against excess rain, snow and ground moisture. Store bagged potting mix up on pallets and covered securely with a breathable tarp. Check soil frequently for saturated bags. Discard any overly wet or moldy soil. For loose soil, contain it in a covered bin, trash can or wheelbarrow. Always elevate soil off the ground with boards or blocks to prevent waterlogging from below. With proper winter storage methods, potting soil can be preserved in quality condition until your spring planting season arrives. Just be sure to inspect it for weeds and pests before using.
