The changing of the seasons is such a natural, ancient event that the shifts in weather are, well, seasonal. As such, many plants have adapted to the survive the dropping temperatures and winter frosts naturally, without needing much interference from you. One exception to this is potted plants.
Plants in pots have different needs than those established in the ground. With less protection from the elements, potted plants are likely to suffer irreparable damage from freezing roots and exposure to wind, rain, and snow. With this in mind, it’s important to give potted plants special consideration when fall transitions into winter.
When it comes to container plants, you have three options: let them weather the storms as is, move them to deeper soil for protection, or bring them inside. Here are some guidelines to help you in your decision making.
Temperature, Light, and Humidity
Some plants can’t handle temps below about 70 degrees while some others can’t handle being too warm, and overall most don’t do well once it freezes. Established plants of yours that have been in the same spot in your yard for years and haven't suffered will likely continue to do fine, so take some time to evaluate the needs of your plants in pots and plan out your winter garden migration. If they like warmer weather, slowly acclimate them to the indoors. If they naturally go dormant during the winter, get them into the ground where they have more protection. If they naturally thrive in a pot, let them stay but offer them some added safeguards.
All other things being equal, remember that your plants will typically not get as much light inside the house as they will while outside in the yard. If your plants needs full sun, it is probably better to plant it in the ground than to expect it to thrive indoors. For those that you do move indoors, consider their need for light and place them accordingly. Moisture needs will also vary depending on what species you're working with this winter. Evaluate your plant selections as to whether they will continue to thrive in the dryer indoor environment.
Relocating plants is always a risky maneuver. In reality, only the strong will survive so use your best judgement when deciding which ones to move and which ones will continue to thrive. Don't bother trying to move or salvage any diseased of pest ridden pots as they can quickly infect other plants in an indoor environment.
Rather than yanking a potted plant from a brisk 55 degrees and plopping it into a balmy 75 degrees indoors, make the transition slowly. When temperatures begin to drop, bring the selected plants indoors during the night and put them back out in the morning. Over the course of a few weeks, allow longer time indoors while reducing time outdoors until the relocation is complete.
Most perennials do just fine outdoors over winter. They are used to the conditions if they are planted in the proper zone and the weather isn’t unseasonably harsh. If they are fragile, they may do better in the ground than in pots though. In milder zones, bulbs will overwinter fine while in other areas they should be dug up and brought inside. Herbs such as lavender, sage, and rosemary can be kept in pots or put into the ground. Roses, berries, hops, and grapes will also do fine either way.
Make sure that pots have proper drainage. Especially in areas that receive a lot of rain, you don’t want your plants standing in a puddle. Plus, that moisture can turn to ice during a deep freeze. On the other hand, if you place your plants under cover make sure they get water occasionally as needed.
In addition to making decisions about which plants stay outside and which plants come in, you’ll need to evaluate the pots themselves. Some materials can hold up to the harsh elements of winter, while others will suffer from her wrath. Here are some different types of pots and information about how to care for them.
Clay or Terra Cotta
Clay products absorb moisture. This means they will crack or chip when it freezes. Whether they have plants in them or not, terra cotta should be stored indoors, meaning you may have to transplant some items to save both the plant and the pot. Even in storage these pots don’t care for the cold so some gardeners keep them half filled with soil to maintain warmth and structure.
Ceramic flower pots are typically glazed to protect the delicate clay underneath. Most ceramic pots overwinter well, but if not in use should be stored indoors.
Because resin is a form of plastic, it can generally handle the conditions that winter brings. The severe cold, however, can shorten the lifespan of your resin pots so if they are empty, it’s best to store them indoors.
Most metal can tolerate the winter months, but the moisture will cause it to rust eventually. You can treat it will sprays and paints or cover it for the winter to increase longevity.
Concrete pots normally do very well staying outdoors for the winter. However, rain and snow can settle in the cracks, then freeze and expand, breaking apart the pot so check the integrity before deciding to leave concrete pots exposed to the elements.
Wood and water don’t typically go well together. You will see the wear on your garden beds, gates, and deck. Flower pots and boxes are no different. Softwoods will break down faster and should be stored inside. More durable woods such as those that are pressure treated, will perform longer, but will benefit from a coat of protective stain every year or two.
Clean and dry all pots thoroughly both so your job is easier in the spring and to avoid bringing pests or disease into the storage area. Do not stack pots, especially those made of clay. This allows them to retain moisture and grow mildew. Instead, stagger your pots leaning one against the next or line them on a shelf with the next layer stacked on top pyramid style. The goal is to allow air circulation.
If you don’t have an indoor space to store your pots, at least get them off the ground. You can stack them on a pallet or even a tarp. Turn them upside down if you can so that they don’t collect rain or snow inside. Wrap large pots that are too heavy to flip over. If you leave any pots on your deck or patio, be sure to elevate them with a plant stand or pot feet.
Also pull all of your outdoor pots into the same area, preferably against the house and under the eaves. Grouping them together provides heat between them. For added protection, you can wrap your pots in bubble wrap or wrap fencing around the group of pots and stuff the area with leaves, straw, or other breathable insulating material.