protected cold frame

Jim McKenney
Tue, 20 Jan 2009 08:14:03 PST
Kathleen, the way you asked your question suggests that you will perhaps be
disappointed with my answer. As far as I’m concerned, the things you ask
about (construction details) probably have little to do with the success
I’ve experienced so far. The frame itself is set into the ground only a
couple of inches; the glazing is a discarded storm door which is so heavy
that only very strong wind is a consideration; the floor (ground) of the
frame is perhaps six or so inched below the glazing. The base is the local
soil (into which some of the cold frame residents are planted). I do not use
shade cloth. This touches on the one big “if” concerning cold frame
management: cold frames are like dogs, they REQUIRE attention at least twice
a day, sometimes even more frequently. They must be opened before the sun
strikes them and closed on all nights when the temperature falls below
freezing. They don’t necessarily conform to the typical work schedule –
they’re the retired person’s play thing. 

I would say that the single most important consideration is the site chosen.
My protected cold frame is right against the house wall, under the roof
overhang and has a SSW exposure. The frame thus has the advantages of heat
seeping form the building and the heat provided by sunlight, heat provided
both to the frame itself and to the brick surface of the building. It’s the
warmest, coziest place in the garden. The two outdoor palms I grow grow
right around the corner with a clump of Aspidistra. 

The frame itself is ridiculously simple: four pieces of 2x6 lumber nailed
together into a 3’ x 6’ rectangle. A discarded glass sliding door serves as
the light. There is no insulation other than the double ply tarp I throw
over the whole affair on particularly cold nights. I don’t bank the sides
with dirt or bales of straw. 

If all of this strikes you as slapdash and improvised, that in fact is how
it all got started. I had ordered a bundle of Jane McGary’s surplus bulbs in
2006 with the idea that I would build a new bulb bed in the back garden for
them. It didn’t happen. As an interim measure, I had already potted up the
bulbs – I just needed a place to get them through the winter. As I was
heeling them in against the house wall, the idea of an impromptu cold frame
hit. So I did it and have not looked back since. 

You can see it here:

The main point I would like to make is this: if you have been thinking about
building or buying a cold frame, but have hesitated because of the cost and
bother, don’t be put off by those considerations. My cold frame was built
for less than $15 – yes, it would have cost a lot more if I had to purchase
the storm door used for the light, but anyone else can improvise. If you can
nail two boards together, you have the requisite skills. It’s not beautiful,
but it was not built to be an eye catching attraction. It’s more or less
hidden behind some fine old boxwood, but even in plain view it’s not

To repeat: the single most important consideration is the site. 

I have other cold frames out in the open garden: a tender plant would
probably not stand a chance in those during the winter.  I use these
primarily for those bulbs which are cold hardy but require careful watering.

Kathleen, you don’t say where you garden. Your local conditions might not
provide the sort of advantages I have here. I’m in USDA zone 7 where, in
recent years, we’ve been having zone 8 winters for the most part. If we go
back to having real zone 7 winters, it might turn out that this cold frame
will require much more careful management. But for now there are times when
it seems almost too good to be true. For instance, in 2006 there were about
240 taxa growing in that small frame during the winter. Many of those were
plants which would not have done well in the house under lights (too warm),
and were not sufficiently cold hardy to survive in the open garden.  

Jim McKenney
Montgomery County, Maryland, USA, 39.03871º North, 77.09829º West, USDA zone
My Virtual Maryland Garden
Webmaster Potomac Valley Chapter, NARGS 
Editor PVC Bulletin 
Webmaster Potomac Lily Society

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