Starting a greenhouse was a natural offshoot of my Community Supported Agriculture (CSA) market garden business; I built my movable greenhouse on rails (a la Eliot Coleman) as well as a lean-to greenhouse and a small version built from cattle panels.
Here's my experience working with them, so you can evaluate the benefits of starting a greenhouse for yourself.
My movable greenhouse (actually a hoophouse) is mounted on wooden rails that are a little more than twice the length of the hoophouse itself. I buried flashing (used steel roofing) around the base of the rails to keep out rodents.
The dimensions of the hoophouse are 20 feet wide and 28 feet long. I framed the end walls in wood; and built a large door in each end for easy access and ventilation.
I also installed a ventilation fan in one end wall. The entire hoophouse, including the end walls, is covered by a single layer of poly.
The hoophouse is relatively lightweight and easily movable by 4 people, with one person on each corner to slide it along the rails.
My lean-to is built from the same hoops; we used half-hoops framed against the south-facing gable end of one of my outbuildings.
The base frame is a 10' x 16' rectangle built out of 2x8. The top of the half hoops are secured to a ledger beam about 11 feet up the wall. End wall framing is made of 2x4 bolted to the hoops.
When I considered starting a greenhouse, I knew I wanted a movable design. Being able to easily move the greenhouse to a new location effectively doubles the greenhouse growing area. I can also take advantage of seasonal and site-specific growing conditions.
For example, the garden where the hoophouse is positioned has both sunny and shady spots. In early spring, the greenhouse is in full sun, to provide maximum light and heat to early crops. Later in the season I cam move the hoophouse to the shadier position, to help prevent overheating.
Beginning in early spring (first week of March in my area, still lots of snow on the ground) I built raised beds in the hoophouse. The 20-foot width of the hoopshouse allowed me to construct 5 beds.
I left about 2 feet between the side walls of the hoophouse and the first beds; this was to provide some distance from the outside cold and also to allow room for me to grow flats of transplants and bedding plants there later in the season.
I direct-seeded the beds with carrots, beets, turnips, bunching onions, broccoli, and cabbage. I installed row cover as well for an additional layer of protection. Despite some heavy frosts, no plants were lost due to cold.
The carrots, beets, turnips and bunching onions stayed in the hoophouse until harvest; the broccoli and cabbage seedlings were transplanted outside in late spring.
I did leave a few broccoli in the hoophouse, to see how they would fare compared to the outdoor garden. The broccoli plants in the greenhouse were harvest-ready 3 weeks before the ones I transplanted out.
Later in the spring, I moved the hoophouse along its rails to the next position. I planted greenhouse-type tomatoes, cukes and eggplant. I expect these plants will also yield a harvest earlier than the outdoor garden.
I subsequently harvested over 100 bunches of carrots, and about 60 bunches of beets and turnips from the hoophouse.
They were ready 4 weeks before the first harvests from the outdoor garden. This early harvest alone was enough to justify starting a greenhouse.
In the fall, I will change the growing order; the hoophouse will remain over the tomatoes, cukes and eggplant to shelter these tender crops as long as possible.
Then I will move it back to the first position, where I will have planted more hardy crops for the fall. This second move means I get triple use from my little hoophouse.
Does this greenhouse production justify the the time and expense? My movable greenhouse (if every component was bought new) would cost less than $2,000.
Hoophouses are usually constructed on a base, so the incremental cost to make it slidable (some more 2x6 and 2x4 for the additional length of rail, more used steel flashing) was about a couple hundred dollars. For this incremental cost (about 10%), I got triple the growing area of a fixed greenhouse.
The value of the extended-season crops and the transplants and 100 trays of bedding plants I grew was more than the cost of the hoophouse; therefore it paid for itself in one season.
Every small farm should consider starting a greenhouse, for fun and profit!
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