University of Vermont Extension
Department of Plant and Soil Science

Winter News Article


Dr. Leonard Perry, Extension Professor
University of Vermont

The North Country Garden Calendar, published jointly by Cooperative Extension in Maine, New Hampshire, and Vermont, has as its theme for 2005 common garden questions each month.  Questions we get, and that you may ask, this month concern the most common winter houseplant problem, how to know what plants will grow in your area, and whether woodashes can be spread on gardens.

With so many exciting new plants and seeds, I find gardeners often don't know where to begin their planning, or how to narrow their search to what may grow in their area.  A good place is the plant hardiness zones, developed by the U.S. Department of Agriculture, shown in their well-known and often seen map.  Find your location on this map, and identify your zone.  These zones refer to "average annual minimum winter temperatures", and so are only guides but good places to begin.

Keep in mind local variations in climate, called microclimates, can modify these zones.  Such variations are caused by altitude, topography (hills and valleys), proximity to bodies of water, or nearness to buildings for instance.  Your local master gardeners, or trained garden store professionals, can help you sort out such variations and their effects.

Plants in catalogs and books will have a hardiness zone or range listed.  These may vary among sources, so it is best to consult several and go with the average.  If you want to be safe, stick with the warmest zone listed for a plant.

The lower the zone number, the colder it is.  Plants have a good chance in your zone, or colder ones (lower numbers).  Depending on those microclimates, they may even survive if rated for one zone warmer (higher number).  So if you are in zone 4, plants listed for this and zone 3 should survive, and perhaps even some rated for zone 5. 

Margaret Hagen, with the University of New Hampshire Cooperative Extension, says that the most common indoor houseplant problem in winter is overwatering.  My own philosophy is, if in doubt, don't water. Here is a case where less is better.

Suspect overwatering if your plants' lower (older) leaves are yellowing and dropping.  Overwatering prevents roots from getting oxygen for proper growth.  The result is root rot, and possibly death.  Rotted roots can't take up water, so plants wilt.  Gardeners often mistake this for dryness, so water more and make the problem even worse.

To avoid overwatering, you can purchase inexpensive water gauges at complete garden stores.  Or look at the soil surface.  Dry soil will often be lighter in color, and will not glisten.  Check the weight of the pots immediately after watering, and water only when pots begin to feel light again.

Use a growing medium with good drainage (soilless ones are best indoors), and use pots with at least one drainage hole.  Plants in pots four inches or larger may only need to be watered once a week.  This, of course, depends on plant size and your home.  Large plants in small pots will need water more often.  Plants in homes with forced air heat will dry out faster than with other forms of heat, especially in winter when the heat is on often.

Lois Berg Stack, from the University of Maine Cooperative Extension, says you can spread woodashes in your garden, or on your lawn, as a substitute for lime.  Wood ashes behave as lime, raising the pH of the soil, making it more alkaline and less acid.  Use only a light layer, as too much can make your garden too alkaline for good plant growth.  It is best to add them according to soil test results.

Wood ashes are good to use, as they make good use of an available resource.  They work more quickly than lime to raise the soil pH.  They also add potassium, phosphorus, and small amounts of other elements important for plant growth.  Don't add wood ashes, though, from burned trash, cardboard, or painted and stained wood.  These may be toxic to plants.

If you'd like to learn more questions and answers each month, as well as daily tips, check out our yearly North Country Garden Calendar online ( If you could use another calendar, or didn't get one over the holidays, you can order this one there, as long as supplies last.

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