Cold frame construction

Jim McKenney
Tue, 04 Jan 2011 10:20:44 PST
For those of you who are regulars of long standing on this list, what
follows is water long under the bridge. But since there seems to be renewed
interest in cold frames, I’ll repeat here some of what I’ve said in the
past. Keep in mind where I am: east coast Maryland where winter sun is
bright and temperatures can drop to about 0º F (about -17 º C). In other
words, this is not sunny California. 


For me, the main advantages of cold frames have been these:

-          they allow me to grow many winter-flowering plants which are
impossible in the open garden

-          they allow me to control moisture

-          they provide a great place to winter marginally hardy plants

-          their economy is very appealing


However, there is one huge disadvantage to cold frames in our climate: they
require attention at least twice a day in the matter of opening and closing
them. A couple of hours of January sunshine will cook the contents of a cold
frame exposed to the sun (and for most purposes you definitely want the
frame to have a sunny exposure). I have not tried the automatic openers
recommended by some people. 


There is no evidence that the temperature inside my most protected cold
frame has ever dropped below the freezing point. For instance, Zephyranthes
grandiflora has gone through the winter in full leaf and never showed any
sign of freeze damage. This year I’m trialing some Paphiopedilum and
Kalanchoë – so far, so good. 


I cover the glass light with a double ply poly tarp whenever the outside
temperature is below freezing. If the daytime temperatures are predicted to
be above freezing, I take off the tarp and prop up the lights a bit to allow
ventilation. If I have to be away for a few days, the tarp remains in place
until I return. 


This has turned out to be a good place to grow marginally hardy aroids such
as Biarum, Ambrosina, Arisarum and Arum along with a big range of other
plants which produce active foliage during the winter. I’ve successfully
flowered one of the Chilean Tropaeolum in this frame, and Nerine sarniensis
has been in this frame since 2005 – although it grows well it is erratic
about blooming.  


Give cold frames a try – you’ll probably be surprised with what you can get
away with. But don’t blame me if your successes in a cold frame soon have
you tearing up the yard and spending big bucks to install a greenhouse to
house your rapidly expanding collections. 


You can see my first cold frame here:


Jim McKenney

Montgomery County, Maryland, USA, 39.03871º North, 77.09829º West, USDA zone

My Virtual Maryland Garden



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