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Using the Greenhouse
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With a little planning and some simple relatively inexpensive structures,
you can extend your growing season at least two months. If you work at it, you
can have at least some vegetables all year round. The two primary tools are (1)
the unheated greenhouse, sometimes called a high tunnel and (2) remay cloth or
row covers.
 Here in Southern New England, our last frost is somewhere around the
end of April and the first frost in the fall is anywhere after the
second week of September, although usually not until mid October in our
location. Nevertheless, we manage to plant lettuce and greens in our
unheated house in mid to late February (usually), and begin harvesting
them around the end of March. We then plant lettuce & other greens
outside under remay cloth in the beginning of April. We also plant
lettuce in the unheated house from September through November and
harvest through Christmas and if lucky, into January. Tomatoes go into
the unheated house in late April (not late May which is the usual
setting out date) and we get fruit in June. We usually miss the first
couple of frosts in the fall since the unheated structures will give two
or three degrees frost protection.
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So how do you do it. Fairly simple. You make an inexpensive
"greenhouse" using pvc pipe for hoops, a perimeter of 2x6 or
2x8 framing lumber and cover it with 6 mil plastic. If you can find it
at a reasonable price, use greenhouse plastic (it will resist UV rays);
if not, get a 20x100' roll of regular 6 mil plastic at Home Depot for
about $40. You will have to replace it every year or two, but at that
price, it does not matter. Even if you buy everything brand new, you
would be hard pressed to spend more than $225-250. We think that is a
fair price for home grown lettuce 10 months a year and tomatoes 4 weeks
before most people. Also, it sure is nice to sit out there in January
when it is ten degrees outside and 81 inside.
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Building the structure. Use standard size lumber and pipe. 10x16 feet
for the outside dimensions works well. Level (sort of) the garden space where
you plan to place the structure. Build a perimeter frame out of 2x6 or 2x8. Use
either pressure treated wood or regular construction grade. (We have some
concerns with the preservatives (Copper chromium arsenate) leaching into the
soil and used regular lumber.) I am not sure how valid a concern this is-I have
heard conflicting contentions. If you do not use pressure treated, expect the
perimeter frame to last five or six years. If your house is longer than sixteen
feet, simply put two boards together and hold them with a wood plate screwed to
both boards. Square the frame up (move it around until the diagonal measurements
are the same) and fix it to the ground with some pieces of 1 inch steel pipe
hammered into the ground and fixed to the frame with 1" pipe clamps. Put a
piece of pipe every three or four feet.
Hoops are 1" or 1 1/4" pvc, 20' long. These are not normally found
at the local home supply store and you will probably have to go to the plumbing
supply house to get them. Set one of the hoops between the two long pieces of
the perimeter frame to get an idea of height and built two end walls using
2x3's. You don't have to be real fancy with the cuts since it doesn't support
much of anything. You can actually fasten the joints with plywood plates made
from 1/4" or 3/8" plywood glued and screwed to your framing pieces.
Make sure you plan for plenty of openings for windows & vents since these
units will get very warm and you need all the ventilation you can get. Today,
February 23, the outside temperature was 26 F. Inside at 11AM, the temperature
was 87 degrees. Put a door and one or two windows on one end wall and two or
preferably four windows on the other end wall. You do not have to be fancy about
windows. Ours are made out of 1x3 pine with a Plexiglas insert (only because we
got the Plexiglas free). Plastic would work equally well. You could also just
use pieces of plywood, although it tends to warp over time.
Windows are important since you really do not need a fan to vent the
structure. If you have enough windows you can vary the amount of
ventilation by opening more or fewer windows. Once you build your two end walls,
nail them to the end pieces of your perimeter frame. Measure, cut and affix a
2x4 x16 board between the two to carry your hoops, the height of the 2x4 being
just below your hoop. Again, if your structure is longer than sixteen feet,
simply scarf two boards together and place a post under the joint. Place hoops
every 3 or 4 feet-we sometimes have a fair amount of snow so I went with three
feet. Hoop goes over the two by four ridge pole and inside the perimeter frame.
Fasten the hoops with 1" pipe clamps both to the perimeter frame and the
2x4 ridge. An alternative is to fasten them to the ridge with pieces of rubber
cut from an old tire tube (sometimes you can find them at a gas station) or old
bike tubes. If you use the pipe clamps on the ridge, put something over the
clamps to prevent them from rubbing holes on the plastic covering. Use a string
from each end wall to make sure the hoops are more or less even. Make any
adjustments by loosening your clamps on the perimeter frame and moving the hoops
up or down as needed. Tighten up your clamps.
Next, cover the end walls with plastic. Fasten the plastic to your end wall
frame with wood battens and screws. Do not just staple it. The first wind would
take it off. Once the end walls are done, cover the hoops with 6 mil poly
leaving an extra foot or so on each end. Fasten the plastic first to the
perimeter frame. Then pull the plastic around to the end walls and screw a
second batten over the first one. The reason to do it this way is when it gets
really hot, you can easily remove the battens along the perimeter frame and lift
up the plastic a foot or two to give even more ventilation. Make up your windows
and doors and put them on with simple butt hinges.
 This is the rosemary plant going on its third winter. It is now 30 inches
tall and going strong. picture was
taken on 17 Feb 2001. Outside temperature was four degrees.
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