Saturday, October 11, 2008

Greenhouses don't build themselves

So here it is, the first cold, inclement weather of the fall. I'm delighted to sit inside right now and avoid the drizzle and the chill. It's just shy of 40 degrees F. outside, and it's 50 inside my greenhouse where I'm growing broccoli, several varieties of kale, Swiss chard, kohlrabi, turnip greens, bok choi, beets, bunching onions, walking onions, leeks, endive, arugula, cabbage and hopefully garlic greens (that is if the bulbs I planted send up shoots). It is possible that the approximatly 35 gallons of water I have stored in plastic containers inside, will help to moderate the climate in the greenhouse. I just finished it last week. Below is my account of greenhouse building.

As fall began to come in this September, seeing the changes in the light and in the length of the days, I decided that it was time to get serious about building that greenhouse. Certainly I must admit that I did not quite anticipate the level of effort needed for this project, or the number of days I would spend with such sore muscles as a consequence of my commitment, but certainly I'm not the first to take on a large project, thinking that it wouldn't be so very difficult. Doesn't this happen in construction all the time?

I think my mistake was perhaps to read in gardening books that describe the "simplest" of greenhouses that could be erected easily and quickly, and to actually believe that this was true. Relatively simple could describe the process I suppose. Perhaps the authors of these books do not live in places that present quite the challenges that one encounters in building greenhouses in Boulder. Maybe they none of them happen to be on the later side of 40 something....

In any case, my greatest challenges involved the necessity of building a structure that could stand up (I hope) to the velocity of the winds we get here in the winter. Certainly the solution to this involves investing more in the structural components and in anchoring them in the ground. Of course the minute one starts discussing anchoring anything in the ground, one must then consider the digging needed and the rocks and gravel to clear out in the process. Some folks just use a post-hole digger. Not in my yard you don't!

My plan was to make bows using PVC conduit pipes rather than PVC water pipes. Schedule 40 PVC conduit has thicker walls in its construction, and it's intended to stand up under UV exposure, so I decided to use that for the bows over the top. For the upright portions of the bows, I decided to use galvanized steel conduit. I installed these over 5/8 inch rebar that I buried approximately 18 inches in the ground and bolted to the sides of the two raised beds that would be enclosed by the greenhouse (see the picture above) and then bent at an angle as needed by the bows. I spaced these bows about two feet apart, which is recommended in snow country. Next, using a heavy gauge wire, I wired 10 foot sections of 1/2" rebar in the center top for the purlin and along the south side. By the time I had finished all this, the whole structure started to "hang together" somewhat and I felt more confident.

Next came the "end walls" with door frames and sills and the vents that I decided to put over the doors. Because I was using odd pieces of recycled lumbar and because I like to build in a rather organic, creative way, this was an entertaining and somewhat time-consuming experience. It also took longer because I decided to add a little root cellar, but that will be the subject of another post. My husband must receive credit here particularly because he volunteered his time and energy one day, and two 4 by 4's of cedar he'd been saving for something special, to build the East end wall pictured above. I also need to give him credit for coming out with the heavy iron bar and digging out the very nastiest rocks when I was fed up with them from time to time.

Once we had the end walls (just frames really) finished, I put up the plastic. This is 6 ml. UV treated greenhouse plastic that I decided to apply in two layers as it's more
durable this way. Cure Farm just replaced a similar plastic on their first hoop house and this had lasted 4 years. To hold the plastic to the bows, I used two diameters of black water hose that I cut into sections with a hack saw and slit longitudinally with tin snips. I positioned them over sections cut from old bicycle inner tubes to protect the plastic and improve their grip. It's important to have inner tube between the greenhouse plastic and the hose "clamps" because the hard plastic edges of the "clamps" can poke holes in the greenhouse plastic. Where the greenhouse plastic needed to be attached to wood, I bought fender washers and self-tapping pan head screws and these did an excellent job of both securing the plastic while distributing forces. It will be easy to take the plastic off in the spring if I want to. I'll see how well this arrangement holds up, but as I borrowed the idea from my observations of the greenhouses at Cure, I suspect we have a workable solution. Another solution I borrowed from Cure and in consultation with one of many references I've been reading, is a tie-down system to keep the plastic down for those really tremendous gusts of wind. I bought seat-belt webbing (you can buy this by the foot from Neptune Mountaineering in Boulder) and two short bungee cords. After installing lag screws in the bottom boards of the raised beds on either side of the greenhouse, I hooked on the bungee cords, ran the webbing over the greenhouse and tied it to the bungees. This is supposed to keep the plastic snug regardless of the natural shrinking and expanding it does with changes in air temperature.
So, after some weeks of struggle, the greenhouse is up. My favorite tools are now my hand-held jig saw, cordless drill, my level and measuring tape, a square, the pick axe and spade. I invested most in the greenhouse plastic and the hardware (lots and lots of carriage bolts, lag screws, washers and nuts in addition to the pan head screws and fender washers). This greenhouse is approximatly 10 x 12 ft. and cost considerably less than what I would have paid commercially. Next time I order plastic though, I will plan on looking for a supplier closer than the excellent resource I used on the West Coast. Shipping costs are rising fast and I expect they will continue to do so. It's not cheap shipping plastic.
I will be happy to take a little vacation now that the cold is upon us.


Kate Goffj said...

Thanks for this information! Do you have a book you can recommend for someone who has never built a greenhouse like this? I don't have the space to build one yet, but I would like to have a reference book for the future.

nisahal said...

Hi Kate,
I used Four-Season Harvest: "Organic Vegetables From Your Home Garden All Year Long" by Elliot Coleman, Barbara Damrosch and Kathy Bray. I also spent time at Cure Farm, gazing long at their greenhouses and occasionaly asking questions. Consider checking or another supplier of books for other more recent books as the library was not very helpful for this type of greenhouse and more books look to be coming out for this audience.