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Overwintering Plants

Barbara Leach, Horticulture Technician, VCE-Roanoke

October 27, 2017

It is almost a little late to be thinking about how to over-winter plants, but when the weather stays as warm as ours has (right up until recently), it is easy to get complacent and just leave plants outside too late.  Ideally, you should think about bringing things inside in September, before the heat comes on.  The change in humidity can be hard enough on a plant, even when the transition is gradual.  Nevertheless, all is not lost if, like me, you waited a little too long because you were still enjoying the last blooms.

For potted bulbs like amaryllis, dahlias, cannas, begonias and others you can tip the pots up on their sides in a protected place so they receive no more water.  If you get a threat of frost, you might need to pull them inside or cover them.  Soon the foliage will begin to yellow.  You want all of the carbohydrate in the leaves and stem to move into the bulb or tuber.  Once the foliage is dried, you can pull it off and store the plants in the basement.  If you have a very cool basement, it takes less space to dig the roots and pack them in some loose, barely moistened potting soil.  When I say barely moistened, I mean like spongy dry soil when you buy it.  If you actually have to add water, try a spray bottle because too much moisture will be the kiss of death for stored tubers and bulbs.  I pack the bulbs and soil in old grocery bags that I have punched some air holes in.  Shredded paper will work for a storage medium, too.  All you need is something to gather and hold enough atmospheric moisture so that the roots don’t shrivel.  If you have the space, you can just stack the pots in an outside corner of the basement, on the floor where it is coolest.  Start watching for sprouting about February, checking weekly.  As soon as you see signs of new growth dig them out and repot in fresh soil.  If you have to pot your bare roots because they begin to sprout, tall plants like elephant ears and cannas can be planted near the bottom of the pot so they are already at the proper depth when set out in the garden. 

One of the most important rules when preparing plants for over-wintering is to wear gloves and be on the lookout for Black Widow spiders, slugs, and crickets.  Widows like to hide under the rim, between or beneath pots.  Also, check for egg sacs.

Plants that are to continue growth may need cutting back and will need to be sprayed for insects.  Insecticidal soap works for most things.  Do not bring diseased or heavily infested plants inside.  It is always a good idea to mix up some soapy dish water and submerge pots in it for a few minutes.  You want critters and eggs to float to the top so you can remove them.  After removal and drainage, flush the pots thoroughly with clear water and scrub the outside.  Plants this saturated will not need water again for a long time, or they may rot.  Likewise, succulents and cacti are not a candidate for this treatment.  As a rule, all plants want less frequent watering in the winter.  Keep them semi-dormant, rather than pushing for new growth.  

Plants that will overwinter outside should be grouped closely, pot-to-pot if possible, in a protected site.  A corner, under outside steps or the deck or somewhere on the north or east side of a structure work best.  You want the pots to freeze and stay frozen, not freeze and thaw all winter.  Leaves, foam block or other insulating material can be packed around the edge to improve hardiness.  Remember, a pot above ground will always be less hardy than a pot that is sunken into well-drained soil.  Either way, the pots will need to be watered periodically throughout the winter, as thaws permit.

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