Not every gardener knows it’s important to know how to winterize fabric pots, but container gardening is becoming ever more popular. Even gardeners with plenty of in-ground space are opting for the addition of container plants because of their mobility and benefits to root health when using cloth pots specifically.
If this is your first year growing potted plants in containers, you may be wondering how to insulate your potted plants or remaining potting soil over the winter. There are many options with many different pros and cons. Read on to find out how!
Why would you need to winterize a planter? Well, you may have cold hardy perennials that go dormant in the winter but still need some protection from frost and freezing weather. Or you may have potted plants filled with potting soil that are left empty after you’re done growing annuals for the winter but would like to save the soil for the following spring.
Potted plants and planters can be brought indoors, but what if you don’t have enough indoor space? Or what if you’re attempting to extend your growing season and don’t have space for growing inside?
The main objective of protecting your potted plants and planters throughout the cold weather of winter is to keep the soil from freezing completely. The surface soil or the top few inches of soil freezing is to be expected. An additional benefit to protecting your planters is that by providing them with a windbreak or other sort of coverage, you can extend the life of these pots.
The methods mentioned below are recommended for cloth pots but are also suitable for most plastic pots and some other planter types as well. However, it is not recommended to attempt to winterize terra cotta or ceramic pots as they are prone to cracking when the temperature reaches freezing. These are better taken indoors, or emptied, sanitized, and stored over the wintertime.
All About Fabric Pots
If you’re here to read about winterizing cloth pots, then you may already have some in use in your garden, or you may be doing preliminary research to see if cloth pots are the right choice for your garden. We’ll briefly discuss the pros and cons of fabric containers to help you determine if they are the right choice for you in your hardiness zone.
It’s worth it to make sure the pros will outweigh the cons before making the investment. Many options exist, but Root Pouch and Smart Pot are popular varieties for beginners. The Root Pouch and Smart Pot are planters made out of breathable, synthetic cloth.
The main pro of growing in cloth pots is the overall root health of your plants. The material of both Smart Pots and Root Pouch grow bags allows the roots to grow through the sides, dry up, and prune themselves off (also known as air pruning). This allows plants to get bigger and healthier with a stronger root system in a cloth planter.
In synthetic planters, metal, terracotta pots, and ceramic pots, when plant roots come into contact with the outer edge of the pot, they turn back in on themselves, which can lead to plants becoming root bound if not appropriately re-potted. For this reason, plant roots in cloth pots have been said to regenerate faster in the spring than their counterparts.
Since cloth has less natural insulation than hard, synthetic materials (especially metal), they require extra protection during the cold winter months – especially if you’re in USDA zone 6 and above. They also have a shorter overall lifespan than containers made from other materials. As a general rule, cloth planters have a lifespan of 2-3 years but can last longer with proper care.
Mulching Pots
In areas that don’t receive hard freezes, adding a layer of organic matter to the soil and grouping the planters together so that they can share heat is your best bet. This works well in USDA zones 9-13. We’ll discuss the two most beneficial types of mulch for a planter below.
Mulch Types
A thick layer of straw, wood chips, or compost on top of your pots will help protect the soil and any overwintering perennial plants. Straw is particularly useful for its ability to retain heat but also allow moisture to pass through freely. Straw also slowly breaks down and fertilizes the plant within the pot.
It can be left in place in the garden for the next season and can help suppress weeds in the spring. It can also be mounded up around the outside of the planter to protect them from a freeze on colder days. However, if the pots are being kept in a windy area, you may need to secure the straw or other mulch with a tarp or other covering.
Cover Cropping
This is an excellent choice if you’d like to try mulching your grow bags or planter but also add a boost to the soil (and, in turn, plants) without using fertilizers. In zones 9-13, there is plenty of time as winter approaches to get a green manure crop going in your container garden.
Hairy vetch, crimson clover, peas, barley, and wheat are all quick-growing crops that can be used as living mulch and protection of plants in winter. Depending on which crop you choose, they can have many benefits, including adding nitrogen to the soil and improving soil compaction. For even more options, check out our article 18 Cover Crops For Raised Beds – those plants work well for fabric pots, too!
The best practice is to allow the cover crops to grow until they flower and then utilize the “chop and drop” method. Chop down the crop and leave the foliage in place as mulch over winter.
In some zones, however, there is not enough time at the end of the fall for cover crops to grow until their flowering stage before the freeze moves in. In these areas, allow enough time for the cover crop plants to grow at least 6 inches in height before chopping.
Season Extension Fabrics
In areas with a colder winter where a freeze is imminent, such as areas that do receive hard freezes like USDA zones 5-8, extension materials such as floating row covers or frost blankets can be used to insulate your overwintering outdoor plants in terra cotta containers – any planter, really – and help them survive. The use of mulch can also be used in combination with these methods for an extra layer of protection.
When using these fabrics to cover container plants, make sure that the sheet does not rest directly on the plant. Use stakes or hoops to keep the synthetic material, burlap, or tarp lifted above the pots and help the plant survive.
Greenhouse Plastic
This type of plastic is made specifically to trap heat but also still allow light to pass through. It is probably the most expensive of the season extension fabrics. However, with good treatment, it will last for several years. Some UV-stabilized plastics can even last for up to 10 years.
If you’re using greenhouse plastic and still have perennial plants, herbs, and shrubs in your garden (rather than empty overwintering planters), then be sure to remove the plastic on warm sunny days as you don’t want to trap too much heat and end up baking your plants. A general rule of thumb is to pull back the greenhouse plastic on sunny days with temperatures above 40 degrees Fahrenheit.
Burlap
Burlaps are probably best known for being used as a sack for potatoes or a bag to transport bulk coffee beans. They are available online with several retailers and also becoming more widely available at big box stores. They’re generally used to wrap and cover overwintering perennial plants and shrubs, like rose bushes and fruit bushes (or blueberries).
You can protect an empty planter if you wrap burlap around the base of the pots. This wrap will help retain heat. Since burlaps are woven, it allows for better airflow, and there’s less risk of accidentally roasting your plants or garden soil on a sunny day. You might be able to find burlaps for free. If you contact a coffee shop or coffee producer, they may have some they can give away. This is a fantastic way to upcycle rather than buy something new!
Tarps
This is the most affordable option (unless you found burlap for free!) and is readily available at big box stores and local stores. Any type of tarp will do as long as it’s large enough to cover your pots. Darker-colored tarps will help trap and retain more heat around a plant. Use the same caution as with greenhouse plastic.
On warmer days, you’ll want to uncover your plants and even your empty grow bags to avoid solarizing the soil. This refers to the process that occurs when too much heat gets trapped in the soil, which will kill any seeds/microbiome in the top few inches of soil.
Solarization is sometimes intentionally used when transforming a large area of formerly weeds into a suitable planting site, but you might not want to kill the soil microbes in the pots that you’ll be planting in come springtime. Therefore, some stakes to keep the tarp above the soil will help.
Structures and Protected Areas
Similar to season extension fabrics, structures and protected areas offer protection to the garden and to plants by retaining heat, keeping the elements off of the pots, and providing additional insulation. Below we’ll discuss the differences between frames, greenhouses, and sheds, which can all be useful in helping to winterize a grow bag or container garden, especially in USDA zones 5-8.
Cold Frames
These frames can be store-bought, homemade, or even constructed from repurposed wood and window panes. They are essentially mini greenhouses and can be made from glass or plexiglass. The benefit of a cold frame vs. greenhouse plastic is that it’s sturdier and can protect better from extreme winter weather events such as heavy snowfall, wind, and even hail.
The pros of cold frames vs. a greenhouse structure is that frames are less permanent and more easily relocated and vented. On warm days just prop open the top of the cold frame in the garden. The downside to a cold frame vs. a greenhouse is that they are smaller and may only be able to hold a plant or two at a time.
Greenhouses
As mentioned above, cold frames are basically mini greenhouses and they can be a great option if you have a small number of outdoor plants or planters to protect. If you have a larger garden, you may opt for a greenhouse in the garden space to keep each plant warm in winter.
They come in a wide variety of sizes and span a wide range of prices, so there’s an option for every budget. They can also be constructed from repurposed window panes and doors if you’re handy. With a larger structure like a greenhouse, there is also the benefit of adding a heat source which can allow you to grow further into the season. The benefit of a greenhouse is that it also doubles as a staging area for seedlings that are hardening off before being transplanted out into your garden in the spring.
Sheds or Garages
A shed or a garage offers much the same insulation as a greenhouse. This is fine for outdoor pots that no longer house a plant but not ideal for planters housing overwintering perennials, as you may still want to have access to them. I also find that whatever I put in my garage ends up “out of sight and out of mind.”
Furthermore, you may have a hard time controlling the temperature in an area that isn’t properly sealed. Unless you are willing to make adjustments and keep an eye on your plants and planters, another storage area may be better.
Burying Pots In-Ground
Another option for areas that receive hard freezes is to winterize fabric pots by burying them directly into the ground. This is especially useful if you’ve taken advantage of a late-season plant sale on perennials but don’t have the time to plant them out into your landscape before the freezing weather arrives or haven’t decided on a permanent place for them just yet. There are two types of burial methods: individual storage and the trench method. Again, this isn’t a good method for ceramic, metal, or terracotta.
Individual In-Ground storage
This method is best suited for cold hardy perennials waiting for a permanent home. Dig a hole in the depth and width of the pot, just as if you were about to transplant it into the earth. Then place the pot directly into the ground. Fill in the earth, so it’s surrounding the pot to insulate it until it can be planted.
Some gardeners use a similar method of placing their empty containers and planters inside larger planters, but this is risky if they do not provide adequate drainage. We all know that water freezes in the winter, which is not what you want around sensitive plant roots.
An in-ground method is a great option if you have limited space indoors for overwintering outdoor planters but still want to offer them some form of insulation. Choose a spot with a windbreak, like one along a fence line, and remember that a dormant plant generally doesn’t require much sun.
Trench Method
This method is similar to the one above, but instead of digging individual holes for each container or plant, simply dig a long trench and place each pot inside of it. If you’d like to bolster this protection, you may add a pile of straw or other organic material like compost to fill in gaps and insulate between the pots.
Empty and Store Your Pots
In certain areas with an extreme cold weather temperature such as zones 1-4, it is not advisable to attempt to winterize fabric pots or, in general, to overwinter pots. This includes areas of the Northern Central United States (northern Maine, Minnesota, northern Wisconsin, the Dakotas, Montana, Wyoming, etc.) and parts of Northern Central Canada.
The best bet here is to empty and store them to avoid damage to the pots and degradation of the soil. This is a good time to inspect your pots. If you notice a white film, this could indicate excess salts from too much fertilizer, but may also be a sign of hard water mineralization. A dark green film could be an indicator of molds and too much moisture.
Before storage, completely empty the potting soils and leftover plant matter that fill your planters, and run your cloth pots through the washing machine along with baking soda and vinegar. This removes debris and insects that might be hanging out within, ensuring you don’t bring them into your house.
Hang them until they are completely dry, and then fold them for storage indoors until the spring. The soil can be stored in a wheelbarrow or other cold hardy container in a protected structure and used again the following spring.
Frequently Asked Questions
Q: Can fabric pots stay outside in the winter?
A: A gardener can keep them outside in the winter with varying degrees of success depending on your growing zone. It’s also important to consider that keeping these pots outside in the winter can reduce their overall lifespan. Sometimes bringing them inside the house is the best bet.
Q: How do you winterize outdoor pots?
A: There are several methods including cover cropping, mulching, covering with tarps or burlap, moving to a protected area, or burying them directly into the ground until spring. The best method for you will depend on your specific hardiness zone and the average low temps you receive during winter.
Q: How do you store fabric pots?
A: For long-term storage, empty the pots completely and run them through the washing machine along with baking soda and vinegar. Hang until completely dry and store in a cool, dry place away from direct sunlight.
Q: How do I keep my fabric pots from getting moldy?
A: Avoid storing them with too much moisture in the soil.
Q: What pots can stay outside in winter?
A: Most pots can survive outdoors during the winter. However, terracotta pots and other ceramic pots are more prone to cracking. The expansion and contraction of any moisture in the soil can lead to cracks in ceramic or clay-based materials. For this reason, it’s not recommended for these types of pots.
Q: How many years do fabric pots last?
A: On average, they last 2-3 seasons but can last longer with the proper protection and insulation from a gardener. Plastic containers do last much longer. However, the trade-off is in the overall root health of your plants.
Q: Can I put potted plants in shed for winter?
A: Absolutely! A shed, cold frame, or greenhouse are all excellent sources of protection for a potted plant during the winter.
Q: Will garbage bags protect plants from frost?
A: Garbage bags will protect plants from freezes, but they are generally not sturdy enough to protect from a hard frost (28 degrees Fahrenheit and below for 5 hours or more). Greenhouse plastic is a better choice for protecting plants in areas with long-term hard frosts during the winter months. Wrap a planter with greenhouse plastics to help susceptible herbs and other plant species survive winter.
