Overwintering Tender Plants
Practicing these overwintering techniques will help you expand your gardening palette without spending a fortune on new plants each spring.
That beautiful red-leaf banana you bought in June looked fantastic through summer’s glory. In fall, the question arises: What do I do now? Rest assured there are options. When cold weather threatens, it is time to get overwintering plans underway for tropicals and tender perennials that spent the warm season outdoors.
The three basic strategies are:
- Bring your plant into a warm, sunny room while the weather is still mild and treat it like a houseplant.
- Let cool temperatures send it into dormancy and store it in a cool, dark location until spring.
- Take cuttings to make new plants and send the parent plant to the compost pile.
There is not a perfect solution for any particular plant, so your best judgement will have to be made based on several criteria:
- How many plants do you need to overwinter and how much warm, sunny space is available to overwinter your tropicals?
- What types of plants are you overwintering?
- Are the plants robust and healthy, or have they struggled through the summer?
Move the Plant
If you are bringing the plant in to overwinter as a houseplant, it is important to first inspect its condition and take note of its size. Look closely for signs of insect infestation such as aphids, scale or spider mites. Aphids are small, soft-bodied insects usually found on the undersides of leaves. Scale are insects that often look like raised bumps on the stem or on leaves. Spider mites are tiny bugs that leave their fine webbing on stems and foliage. All of these critters are detrimental to the health of houseplants and should be addressed before bringing the plants in for the winter. A strong jet of water may be enough to remove many of the bugs, but other solutions include a topical spray of horticultural oil that will smother adults and eggs or a systemic insecticidal treatment that will kill bugs as they try to feed on the plant. I recommend treating in that order, going from least to most toxic.
Another maintenance task that is better done outside rather than in is pruning. If it is time for a trim, do it before bringing the plants in and avoid the mess. Aggressive growers will benefit from an aggressive cut-back. As a side note, fertilization should cut back when the plants come indoors for two reasons: Many will not use the same amount of fertilizer in winter, and those that could use it would only outgrow their allotted space..
As a general rule, especially when space is limited, sick, weak or infested plants should not be kept. These weak plants may be good candidates for taking cuttings. It does not benefit the other plants to have a likely host for disease and insects kept in close proximity for 6 or 8 months. Other candidates for cuttings include unwieldy large plants, or those that grow very quickly. Take several cuttings for each plant, because success rates are rarely 100 percent. Keep the cuttings in a warm location where they can root in and grow well.
Wait Until Dormancy
As overnight temperatures drop into the 40s, dormancy is triggered in many tropicals. At this point, you can stop watering unless the soil has dried out. Move the plant to an unheated, dark location that will stay in the upper 40s or lower 50s. Basements, garages or unheated sun porches are potentially good locations. Use boxes or black trash bags (loosely) to cover the plants if the room is not dark enough. Check on the plants every week or so to see that they are not completely dried out. Water sparingly if needed. (Woody plants should not be trimmed ahead of this treatment. Herbaceous plants should be allowed to turn brown before cutting back. Bulbs should be dug up and wrapped in newspaper or bagged in peat moss. The dark, cool conditions are the same for all types of plants.
Plants that are only a zone or two away from their hardiness zones, like a zone 9 Sago Palms growing in my zone 7 landscape, may only need temporary protection when cold fronts are moving through. Be sure to address soil drainage issues for these plants at planting time; as hydration is a key component for cold protection, and by the same token overwatering a dormant plant can rot its roots. Mulch these plants well for winter.
An in-ground planting will benefit from a frost blanket wrapped around the entire top to help it endure a cold spell. For a few extra degrees’ protection, cover the frost blanket with plastic. Never use plastic directly against foliage because frozen condensation will burn the foliage. Remove this covering as soon as the weather breaks. Outdoor containers can be wrapped with styrofoam or bubble wrap to mitigate temperature fluctuations. Again, be sure to water well ahead of cold weather and wrap the top of the plant to protect it through extreme temperatures.