Building an Inexpensive Greenhouse
By Chris Pratt
It is late fall, the leaves are gone, and the nights are cold. The garden has been bedded down for the winter with a
green manure crop to prepare it for spring. You come in with an armload of wood, take off your winter coat and set
down to a fresh green salad with loose leaf lettuce, spinach, shallots, basil and tomatos. All picked fresh moments ago.
Welcome to the Greenhouse!
One cannot say enough about how nice it is to have a greenhouse. Prior to building it, we never had a season where
jalepenos and cayenne peppers (our passion at the dinner table) would come to full maturity. Kim learned how to make
many jars of green tomato salsa (by necessity). The growing season in Western Washington State is barely
adequate to grow a successful garden.Our greenhouse is a necessity rather than a nicety (we just didn't know it prior
to building it).
We saw an article in Countryside Magazine that talked of using welded wire stock panels (wires welded to form a fence
partition, see Figure 1) with both edges held down to form a quansot hut style greenhouse. This design called for pounding re-bar
into the ground and wiring the edges of the stock panels to the re-bar. The top of one panel is then wired to the bottom
of the next and so on. At the ends, you use some sort of framing to stiffen. Everything is then covered with translucent
This is how we planned it and how we based
our purchases, but as so many of our projects go, quite different from what we built. The first thing that had to go was
re-bar. The place we picked for the greenhouse, had a substance that while appearing to be dirt, is really closer to
concrete. The re-bar lost the contest and would bend rather than be pounded in! The second problem was headroom.
The stock panels would not be high enough if they were flush with the ground. The last was the fibreglass panels. The
fellow at the building supply talked us out of this as he felt they would be cracking constantly at the place they were
wired on. On to plan B.
How we built it
What we built was actually a frame of 4x4s to support the wire structure. These were placed in a "basement" on pier
blocks. The stock panels were attached to the frame, the ends framed, and greenhouse plastic placed over the
The process began by scraping out an 8 1/2 x 22 foot hole approximately 12 inches deep using
out loader. Then we leveled it by hand. We placed the pier blocks where they would appear to provide the greatest support and
created a 8 x 20 square of 4x4s at just above ground level (each 4x4 was attached to the next by steel plates and screws). This 4x4 frame was
nailed to the pier block's steel bracket.
The frame being completed, we got out the bolt cutters and cut off the little ends sticking out
on the stock panels (see Fig. 1). We then laid the stock panels out so that one end was flush with one side of the
4x4 frame. This end was nailed down using giant fencing staples (we did not drive these home at this point so that we could
make any adjustments that might be necessary). The BIG MOMENT. We made the first bowed section by one of us
pushing the free end towards the center (see Fig. 2).
The free side was now nailed to the
other side of the frame and viola... we had something that resembled a structure. We repeated this procedure for 5
stock panels using baling wire to wire each one to the next until we had something similar to Fig 3.
Using all those old scraps of 2x4s that are left over from projects, we framed the ends. The north end was given a
special treat, 2 sections of 1/2 inch plywood (something we avoid using since it cant be milled) with holes cut out for
louver vents and a fan. The south end got a screen door cut down to about 5 1/2 feet and 2 louver vents. The entire
structure was covered with a professional greenhouse plastic.
To seal in the "basement" we bought sections of a type of board that contains concrete. Using a worm drive skil saw
we cut these boards in strips to go from the ground (down in the hole) up to the edge of the 4x4s. These were then
sealed at the top with a sealer, and backfilled at the bottom with dirt. We then filled the entire interior with about 6 inches
Though running water would be nice, we decided to use a 50 gallon food grade olive barrel to hold the water we use.
This has to be filled once in a while but it has the advantage of storing heat (it is a dark gray color). We purchased
a plastic valve, a section of pipe with threads on both ends and some plastic nuts to go on it. We cut a hole the size
of the pipe, put a nut and o-ring on both the inside and the outside of the hole. The we screwed the valve on the end
Since the barrel spigot is at the bottom, we have an old cable spool that we set it on. It was free and is strong enough
to hold the barrel when it is full. The bottom section of the spool doubles as storage for all the little tools we keep for
We limped by for sometime with a small thermostatically controlled electric heater. Even during the summer there were
occasions when the cool of the night would allow the temperature to drop below acceptable limits. We are in the process
of installing a propane heater (non-vented) and a large tank. This should be the most effective method of keeping the
greenhouse warm. We also purchased a cover that can be placed over the entire structure in the evenings and even
left on during really cold spells. It reduces the light by a small amount but provides excellent insulation.
While this may sound like a lot of bother, it is well worth the effort when you see the results.
We are using Halide Track lights to extend the daylight. To achieve coverage of the entire growing area required two
lights and tracks. These make a full pass every 40 minutes. The downside of this is the cost. Each bulb is 75 dollars.
With the short days of winter, we would not be able to keep the peppers blooming without them.
The first morning we had the greenhouse complete and covered, the temperature soared to 120 inside. We realized
that without good cooling, we had simply created a solar oven. We installed a vent in roof, 4 solar-hydraulic
vents in the ends, and a fan in the north end.
The vents are really inexpensive for what they do. They have a hydraulic fluid that opens and closes them based on
temperature. No motors, pumps, or electricity, just very sensitive fluid. These ran about 14 dollars apiece. We made
covers for the vents that can be put on at night so that no heat can escape through the louvers.
The fan is built for greenhouse use. This is important because the moisture can ruin an electric motor. There are louvers
that open when the fan is on. It is hooked to a thermostat that turns it on when the temperature reaches 70 degrees.
We found that we must open the glass in the screen door to allow the volume of air required by the fan. The small
vents are insufficient to avoid a low pressure situation.
Growing Boxes and Tables
Plants are set on tables in the greenhouse instead of the floor so that warm air
can circulate below them. These tables are typically called "benches". After
looking at expensive benches in several mail-order catalogs, and after looking
at more benches in books checked out from the library, we built our own
benches out of used lumber. We purchased white plastic latice for the
top of the benches. The tops can't be solid... they need to let air and
water through. We built a total of three 8 foot long benches. Two
were set on one side of the greenhoues, one on the other. On
the side of the greenhoues with only one bench, we built a 9 foot
by 4 foot raised bed (also out of used lumber).
We also built four "growing boxes" especially for raising salad
vegetables. The boxes are made of used wood and are about
24 inches by 16 inches, and about 6 inches deep. In the
first box we planted lettuce, spinach and shallots. We planted
the second box 3 weeks later... the third box 3 weeks after that...
and the fourth box 3 weeks after that. By the time you have
planted the fourth box, the first box is ready to eat and
provides about 3 weeks worth of salads for us. We then
replant it and move on to eating the second box which is
now ready to eat. And so on, we cycle through the
salad boxes in a continues eat-plant cycle.
In the past we have grown the following crops
in our greenhoues:
- Many Varieties of Peppers
- New Mexico
- Chile De Arbol
- Bell Pepper
- Loose Leaf Lettuce (2 kinds)
- Romaine Lettuce
- Herbs (Cilantro, Basil, Oregano, Lemon Balm, Marjoram)
- Potatoes (Yes, Potatoes!)
- Brussel Sprouts
While we ended up investing quite a bit on our greenhouse (this is relative, many people spend more on a new TV),
we have not even approached the cost of buying a
pre-fabricated shell. Our money is tied up in equipment to make the greenhouse a year-round productive garden rather
than being tied up in the basic structure. The lights, heating, and cooling represent the majority of the cost. If the
costs seem restrictive, remember that you will pay the same money over a year to get fresh organic produce during
the off-season. For us, hot peppers, sweet peppers, and tomatos alone can nearly justify the cost. To go a step further,
the greenhouse can produce income buy selling off culled plants or starts at the beginning of growing season. The size of
our greenhouse provides ample produce for us. If we were to add two more stock panel sections, the extra space
could be used to grow produce for local markets, and this is without any additional costs (beyond building the structure).
Many components in our greenhouse can be obtained second hand for free or nearly nothing. These are:
Stock Panels (any farm with cattle)
Pier Blocks & 4x4s (a good replacement would be bricks or rocks with mortar and a 2x6 ledger on top)
Louvers for Fan (scrap yards)
Food Grade Water Drum
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