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In 2003 I went searching for a new place to live. My succulent collection had outgrown the few outdoor benches I had constructed, I had started sowing seeds and couldn't imagine where all the new plants would go, and I'd grown tired of natures assaults on my plant collection. From wind and rain and scorching sun to browsing deer and marauding raccoons, I was faced with a constant barrage of broken pots and labels, waterlogged plants, and mayhem. I needed a yard big enough for a greenhouse. I am also a renter, so whatever solution I found, I knew that it had to be portable. And because my income was limited, the solution had to be cheap. Now, seven years later, the proof of the utility of my home-built greenhouse is secure, and I want to share some of what I've learned.
My 20 x 24' greenhouse, fully furnished, cost me about $3800, or about $10 per square foot of useful bench space. Seven years later the plastic film that protects my plants from the elements needs replacing for the first time, and there's material left in the original roll to do this at no additional cost. I have grown literally thousands of plants from seed in this structure, and it has become a source of inspiration and joy for me, my friends, and my community.
My inspiration in the design of my greenhouse came from the large structures at Steven Hammer's nursery in Vista, California. His houses are framed in metal poles that fit together into welded corner and angle units, and a wooden frame is hung from these tubular structures using off-the-shelf hardware. To these wooden beams shade cloth, horticultural plastic, and a door are attached.
I did some preliminary searching for companies that make these portable metal building frames, which are normally marketed as "party tents", temporary buildings that can be constructed and deconstructed within a matter of hours. The vertical, horizontal, and diagonal (roof) members are made of the same galvanized steel material used in the construction of a chain link fence. A larger diameter tubing is used in the construction of the corner pieces that join the metal tubes together, and just a few different standard parts need to be manufactured by the party tent company.
It pays to search around for a local company who does their own fabrication, and I found great service from A&L Products in Ceres, California. I decided to pay an in-person visit at their plant in the Central Valley to see what they could do. Many of the party tent companies you can find online offer only a range of standard sizes and shapes, and this makes sense when you consider that it is not just the frame, but also the vinyl covering that the companies must manufacture. In my case, though, I wanted only the frame, and I hoped that someone could make a frame in the exact size I wanted. I was amazed that with A&L I could specify exact dimensions, and with just a few click of a mouse they were able to generate a drawing and a parts list for my A-frame-roofed building. For a 20 × 24' structure (8' wall height) the total cost for the frame was $658.21, tax included, and the materials fit in my pickup truck with plenty of room to spare.
The back corner of my lot was already flat(ish), but it was covered in a bramble of small trees when I moved in 2001. I spent about a week preparing the ground, but because our winter rains had already begun, I didn't care to spend more time getting out every tree root or to perfectly level the floor area of the greenhouse. I had a friend (SF–club member Jeff Shipley) over one afternoon in January, and we got the entire metal frame set up in less than an hour.
The vertical poles sit in A&L–provided "mud feet", metal plates with a short piece of rebar sticking out of the bottom, a tubular metal fitting on the top. In a more permanent installation, the wall poles could be sunk in concrete (and larger-diameter poles can be ordered for additional stregnth and permanance), but in keeping with my portability requirement, the structure was secured to the ground with nylon rope tied to rebar: A 4' piece of rebar is driven at an angle about one foot into the ground near the greenhouse wall (inside or outside the structure, as you see fit), a length of nylon rope is tied to a horizonal bar of the metal structure and to the rebar, and the rebar is pounded further into the ground, drawing the rope tight. Four such stays seemed sufficient to secure the structure in my rather protected back yard.
Next came the wooden frame. If I had had to build the entire structure out of wood there would have been a lot of technical measurements involved, the material costs would have been high, and the time required for construction would have been enormous. But because the wooden parts in my design serve only as points of attachment for the plastic sheeting and a doorway, and because they simply (and literally!) hang from the metal frame, all cuts and measurements were simple, and rather imprecise. I decided that the plastic roof would extend from the ground on one side of the greenhouse, up and over the apex of the A-frame roof, and down to the ground on the other wide. The two uncovered end-walls would be covered only in shade cloth. It was easy to see that I needed a ring of 2 x 6" boards around the base of the entire structure and around the triangle-shaped area of the A-frame on each end, and off I went to the lumber store for treated Doug Fir boards.
Home Depot sells metal clips, called tension bands, used in chain-link fence constructions. These hook over the metal bars of my greenhouse frame and have a through hole which allowed me to screw them directly to the boards along the roof line. The metal clips and tie plates (20 each of two different kinds) came in at $18.60. I used 1.5" deck screws to hang the wood members on the metal frame, and I only needed help marking the angles at the roof apex and supporting boards as they were hung in place. No more than six hours was required to cut and hang all the wood pieces.
Along the front of the greenhouse I placed an additional vertical board between the "baseboard" and the board hanging along the roof line, leaving a space wide enough to hang an aluminum "storm door" I bought at Home Depot for $127.
The floor of the greenhouse must be a serious consideration. I guess ideally a cement slab would be poured, but this was both out of my budget and contrary to my portability philosophy. To me, having a floor that was relatively durable, weed-free, and sweepable were of primary concern. I settled on a black, woven, UV-resistant horticultural polypropylene material, which is sold (as a weed barrier) by the roll for typically less than 10 cents per square foot. One 6' × 300' roll of this Dewitt-brand ground cover would cost me $75.43 from McConkey (a large horticultural supply house, which happens to be happy to deal with individual members of the public). Floor installation was trivial. The 6'-wide sheets were rolled out in parallel overlapping swaths, and then "nailed" into the earth below by driving a thick 4"-long nails every few feet along the ground cloth's edges. Washers serve to capture the nail heads and thus prevent the nails from tearing through the floor sheet.
It's worth considering how you will sweep the greenhouse floor before laying down the sheet. I find that certain parts of the greenhouse are marginally harder to clean, because my sweeping direction (out of a corner and toward the center) sends dirt and perlite under the flaps where the floor covering sheets overlap.
It is essential that the plastic film used to cover the greenhouse be horticultural grade greenhouse plastic. Such UV-resistant film that is guaranteed to last at least five years. It's not cheap, but mine has only just begun to fail after seven years, and I'm certain its demise was hastened by a tree that fell onto my greenhouse last winter.
I bought a 48' x 100' roll of plastic for about $250. This piece, which comes cleverly folded and rolled onto a 12' cardboard tube, is enough to cover two greenhouses my size, which means I now have enough material on hand, carefully stored in my basement, to re-cover the greenhouse this winter at no additional cost (not that removing the old film and getting the new sheet in place will be easy with the greenhouse full of plants!).
The cheapest way to install the plastic sheet is to staple or nail the plastic directly to the wooden frame, but this must be done with care. The ends of the plastic should first be wound around wooden slats so that the pulling pressure felt at the connection points is distributed along the length of the plastic sheet, and not just at the points where the plastic is nailed. Better, however, is to use one of the systems designed to hold greenhouse plastic in place. I found an elegant system by Agralock that consists of an extruded aluminum base that screws onto the greenhouse frame. The plastic film is laid across a metal slot, and then an second aluminum slat snaps over the plastic and into the base strip. The design is such that the plastic is secured against the sort of lateral tugging that wind will exert along the direction of the plastic sheet, but a vertical tug easily pops open the assembly, making replacement of the plastic literally a snap. At just over $200 for all the hardware I needed (again from McConkey), the ease of installation seemed to merit the expense. And the end result looks petty slick. Not one bit of the 144' of installed hardware has failed in seven years.
Shade is a crucial consideration, and I decided that 30% shade cloth would suit the types of plants I grow: mostly succulents, with a strong focus on mesembs and cacti. I'm in cool but fogless Oakland, but in hotter climates you might want to go for 50% shade. If you want to divide your growing space into areas suitable for seedlings or plants that would thrive under less light, you can consider hanging layers of shade cloth to achieve the ambience desired*.
It is an inescapable axiom that the benches in your greenhouse will cost as much as the structure, though you'll rack your brain trying to get around this fact. Many commercial greenhouse benches exist, but I had my own ideas of how to proceed—and save money, I hoped. I can report that no money was saved in the construction of my benches, but my design has proven robust, portable, and practical. I began with size.
I like to keep all my plants in 18" square plastic flats, since these can hold twenty-five 3" or sixteen 4"-square pots. Therefore, my benches are 3 × 6' and fit exactly eight flats each. I estimated that I could fit 20 such benches in my greenhouse (but you will plan better than I did). The bench tops were constructed with 1 × 4" redwood: two horizontal (or lengthwise) members, each 6' long, crossed by eight 3' members spaced such that flats are evenly supported from below. These lengths are readily cut from 12' boards ($360) and assembled with two screws at each board intersection. Total time" about six hours.
The legs of my benches were fabricated at my request by A&L, the maker of my greenhouse's metal frame. The same galvanized metal tubing forms the bench risers, and because I am very tall, I elected to set my benches on 36" legs. This has proven perfect as a work and observation height for me, but my bench design allows you to set your benches at whatever height you want, with only a trivial difference in cost. The real expense of the design came in the manufacture of the hardware that attaches the legs to the bench tops. I designed a simple metal plate with a welded-on sliding-fit metal tube to accept the leg. Half of the 160 parts I ordered have two through holes; these screw onto the bench bottoms. The other half, holeless, sit below the feet on the greenhouse floor. The assembled benches seem quite wobbly when assembled, but once weighted with plants they are perfectly stable. My 20 benches (some 360 square feet of bench space) cost just under $1650.
With seven years experience, I can offer a few improvements on the bench design. First, the assembly would be greatly simplified if the legs were secured into the connecting tubes at the bench bottom and feet with set screws like those that hold the building frame together. If the assembly tubes on the legs were also longer (say 4" rather than the 1.5" I specified), the legs would likely stand straighter, and the height of each leg could be individually adjusted to accommodate uneven flooring. Set screws would have added $1 to each part ($160 total). Plating to prevent rusting of the plates would also have added a dollar, and is probably not worth the added expense.
In overall design the greenhouse I designed has one glaring shortcoming, and that is in the space efficiency. I chose the structure size independent of a floor plan, and realized only later that if I had first planned how I wanted the benches to be arranged in the greenhouse, this plan would have dictated a slightly different size for the floor area. When planning your own greenhouse, I'd advice first drawing a floor plan. Using paper cutouts or a computer drawing program, take time to arrange your benches, space out your aisles, and imagine where your door will go. 20–24 inches should be considered a comfortable minimum space between benches. I aimed for 18" aisles, imagining only that the ability to place 18" flats on the floor was important. It works fine for me, but my fat friends can't walk around in there!
My benches, with their spindly metal legs, offer an additional advantage I hadn't anticipated. I discovered that ants are my number one greenhouse enemy, since they spend a lot of time farming aphids and mealie bugs, moving pests from plant to plant. The spread of sucking insects can be greatly slowed by eliminating ants form your benches. Blocking their path up the metal legs of my benches was accomplished with a ring of tanglefoot around each leg. Tanglefoot is a sticky plant resin that ants can't cross, but make sure you apply it where clothes and fingers can't reach. I applied strips of packing tape around the bench legs first, making removal of the tanglefoot much easier. But don't underestimate the cleverness of ants. No other part of the bench, or its contents, should touch the greenhouse walls or shade cloth, or the ants will jump right back on!
I could go on indefinitely about the hows and whys of my setup, but instead I'll pose a few last thoughts and questions for you to ponder for yourself: Consider how you're going to run a rose into the greenhouse. A space as big as mine requires watering by hose, but my nearest faucet is fifty feet away. Will you keep soils and pots in the greenhouse, and if so, how will you store these things and keep them looking neat? (A messy greenhouse is a distraction from the plants!) I have hung wood beams from the metal roof beams of my greenhouse in order to attach hooks and chains for hanging baskets, but be aware that it's hot higher up. Hang a min-max thermometer somewhere in the greenhouse so you can learn to gauge your daily, monthly, and annual temperature extremes. Will you run power and put up shop lights so you can work after dark, or will you do as I have done and allow the sun to dictate when it's time to go inside? Establish a spot for repotting and keep it clear—your seedlings are going to be needing a lot of attention as you strive to fill the house. Later you'll need to have room to stage plants as they leave, perhaps to be sold at your local cactus club. One things for sure, when you finally get your greenhouse built, your life with plants will never be the same again. My greenhouse is a refuge form the world, and I love it!
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| Metal "party-tent" structure |
$613.00 |
| 8’ 2 × 6” Douglas Fir, (6 boards) |
$34.00 |
| 10’ 2 × 6” Douglas Fir (7 boards) |
$45.00 |
| 12’ 2 × 6 Douglas Fir (8 boards) |
$68.00 |
| Screws (#6 × 1.5” grab-guard, 1 lb) |
$8.00 |
| Aluminum door with window |
$127.00 |
| Tension bands (60) |
$22.00 |
| Washers (40) |
$3.00 |
| Tie plates (30) |
$11.00 |
| Plastic Floor Sheeting |
$80.00 * |
| Floor nails and washers |
$15.00 |
| Horticultural plastic film (48 x 100’ roll ) |
$250.00 |
| Agralock base (12 12-foot pieces) |
$105.00 |
| Agralock top (72 2-foot pieces) |
$102.00 |
| Shade cloth |
$693.00 ** |
| $2175.00 |
| Wood for table tops (60 1 × 4” rough cut heart redwood boards) |
$310.00 |
| Screws (#6-1.25” grab guard, 5lbs) |
$30.00 |
| Legs (80 galvanized steel poles, 36” long) |
$180.00 |
| Table Feet (160, custom manufactured) |
$1120.00 |
| $1640.00 |
| $3816.00 |
Parts list and prices (tax and shipping not included except: *shipping included, **tax and shipping included.
All values rounded to nearest dollar.) |
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