Posted by Beth Steele on 11/12/2017 to FAQ (Frequently Asked Questions)
You're probably here because winter is just around the corner and you have an ornamental shrub growing in a pot outdoors that you're worried might be damaged or killed by cold temperatures. Before you get too worried you want to first check the USDA Zone for the plant, and then know the USDA Zone you're in.
If you're not familiar with the USDA Plant Hardiness Zones they are the standard by which gardeners and growers can determine which plants are most likely to thrive at a specific location. The zones are based on the average annual minimum winter temperature, divided into 10-degree F zones. For better accuracy, the USDA has divided each numbered zone into two parts:, such as 7a and 7b.
To find the USDA Zone listing for a specific plant species or variety you can find it in several locations on every plant page in Wilson Bros Gardens. You can use the Plant Search at the top-center of any page in the website to find a plant you're looking for. It's best to type just one word in the search box. For example, if you are looking for Autumn Embers Encore Azalea you can type "embers" or "encore" in the search box. Once on the plant page you'll find the USDA Zone listings under the USDA Zones Map tab, directly under the main plant photo, and in two locations under the Description tab.
How to know if you need to overwinter a potted shrub indoors
The roots of potted shrubs are more exposed to colder air temperatures than are the roots of shrubs growing in the ground. During the winter, soil temperatures are usually 10 to 40 degrees or more warmer than air temperatures. So, if the potted shrub you are concerned about is listed as cold hardy to two full USDA Zones north of the zone you're in then there's probably no need to be concerned about cold damage to your potted plant or having to bring it indoors for the winter. That said, if and when temperatures are forecast to drop well below what they normally would in your area, you can always bring the plant indoors for a few days or until temperatures have risen back to above normal.
On the other hand, if your potted shrub is listed as cold hardy only to the zone you're in, or one zone above, you might want to consider overwintering the plant indoors through the entire winter season.
How To Overwinter Potted Shrubs Indoors
You can overwinter ornamental shrubs in a heated or non-heated interior space in which the temperatures don't drop much below freezing. This could be a garage, basement, shed, sunroom, greenhouse, cold frame or other interior space.
First, Clean 'Em Up
Before you bring your potted plants indoors for the winter, rinse them off good with the water hose. Then, closely inspect the foliage for insects or other critters that you don't want to bring indoors. Make sure to check the undersides of leaves. If you find any insects pick or spray them off before bringing the plants indoors. You can also spray the plants with a safe insecticide listed for indoor use, such as insecticidal soap. Be sure to spray both the upper and under sides of leaves. When using insecticides always read and follow instructions on the product label.
Non-Heated Interior Spaces
When overwintering in non-heated spaces you'll be maintaining the plants in a dormant or semi-dormant state in which they will require less attention to watering. Since the plants won't be actively growing you'll want to water them sparingly to keep them on the dry side; maybe once every 2 or 4 weeks, and there will be no need for fertilizer. Just provide enough water to keep the soil in the pot slightly damp. Allow the top inch or two of soil to dry before providing more water. Make sure the base of the pot isn't sitting in a saucer or tray of constant standing water, which can cause soggy soil and problems with the roots. It would be best to fill the saucer with some small gravel or pebbles to avoid this problem.
If possible, try to provide some light for sun-loving shrubs. Too much or total darkness can cause partial to full defoliation on many types of ornamental plants. This can be achieved by situating the potted plant near a window or under lights. Plants that like morning sun might do best near an east facing window. Plants that like full sun (at least 7 hours of sunlight per day) can be placed near a west or north facing window.
Environmental conditions indoors during the winter months are often rather poor. Low light levels, hot drafts, low relative humidity, light exposure and other environmental factors can be stressful to plants. The stressful conditions may cause plants to shed leaves or otherwise perform poorly. Inside a heated home, some shrubs will continue to grow, producing new growth and maybe even flowers. This can be a problem with some types of shrubs as they might require a chilling period to bloom on time when outdoors. Plants that normally bloom in the spring outdoors might bloom in the winter indoors, and then not bloom in spring. That said, if you keep the plant in a cooler environment such as a basement, and away from heater vents, this can be helpful.
Maintaining proper soil moisture in potted plants can be a little tricky because the soil might dry out more quickly indoors than outdoors during the winter months, especially if a potted plant is placed near a sunny window or heating vent. That said, if a plant is dormant or not actively growing it may not require as much water. So be careful not to overwater. Soils that stay constantly soggy can cause damaging or life threatening problems such as root rot. When the top inch or two of the potting soil has dried provide some water. If the pot is sitting directly on a saucer, empty the saucer of water after watering or fill the saucer with small gravel or pebbles. Doing so will help to prevent soggy soil and root disease.
Too much or total darkness can cause partial to full defoliation on many types of ornamental plants. If possible, try to provide light according to the plants sunlight preferences, which can be found under the Description tab on any plant page in WilsonBrosGardens.com. Adequate levels of light can be achieved by situating the potted plant near a window or under a grow light(s). Plants that like morning sun might do best near an east facing window. Plants that like full sun, which is at least 7 hours of sunlight per day, can be placed near a west or north facing window.
Due to heating systems, indoor environments are often drier than outdoor environments. In lower humidity conditions some types of plants will respond by shedding leaves. This is a natural response since the plant is attempting to conserve its moisture loss by reducing the number of leaves that are transpiring moisture. This can be seen as a form of shock, but because dry winter conditions are slow to develop, it may occur quite gradually. Resting the pot on a tray of pebbles kept constantly wet may help with humidity levels, however, as mentioned, don't sit the bottom of the pot in a tray of water as this may cause the soil to become oversaturated. You can also mist the leaves of the plant occasionally to prevent them from drying out. If you use a humidifier in your home that keeps the humidity at or above 40 misting usually isn't necessary.
Temperatures & Drafts
If an indoor potted shrub is frequently exposed to cold or hot drafts it may begin to drop healthy leaves. Try to situate indoor potted plants away from heating vents or radiators, or use a sheet of cardboard or some other object to deflect the draft away from the plant.
If one is attempting to grow a fig tree indoors year round, and the leaf drop is preceded by leaves gradually turning yellow or pale green, it's possible your plant is reacting to insufficient fertilizer. Provide a dose of fertilizer at half the recommended rate on the package. Whether it's a granular or liquid fertilizer, make sure it is listed for use on potted plants.
Certain insect pests, such as mealybugs, spider mites, and scale, can cause problems on indoor plants. If you notice leaf discoloration or, it's a good idea to check the top and underside of leaves carefully for insects. If you see pests, treat the plant with insecticidal soap or other insecticide safe for use in interior environments. SEE: Homemade Insect Control Sprays For Indoor Plants
When a potted plant is brought from outdoors to indoors, you can take steps to prevent defoliation and other problems due to shock from dramatic changes in temperature, humidity, light levels, and/or watering habits. To avoid shock, if you are transitioning a plant from outdoor conditions that are much different from the current indoor conditions, do so gradually - giving the plant increasing long visits indoors until it is acclimated to the conditions. Do the same when moving the plant backoutdoors for the warm season. If your plant loses some or all of its leaves there isn't much you can do about shock once it occurs. In most cases the shock is a temporary condition; as the plant adjusts to new conditions, its health will return. Keep in mind that a plant with fewer or no leaves will not drink as much water. Check soil moisture closely before watering, and only provide water when the top inch or two of the soil has become dry.
When To Move A Plant Back Outdoors
The best rule of thumb is to wait until nighttime outdoor temperatures are consistently within about 10 to 20 degrees of the indoor space where you are keeping the plant. That said, it's a good idea to gradually acclimate the plant over the course of a few days by taking it outdoors from early morning to late evening and then bringing it back indoors at night, especially if nighttime lows will drop more than 20 degrees lower than the indoor temperatures.
Hope this information was helpful. Don't hesitate to contact us if you need more details or have any other questions.
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