By Bev Johnson

Master Gardener 

Bunkey decided he has enough “gardening smarts” to start his own plants in his own greenhouse. Before he spends any money, there are a few things he needs to know.

He may or may not recover the cost of the building for years, especially if he is only growing plants for his own garden. If that isn’t a problem, there are still some things to think about before he starts. One of the vital decisions is where to build. The site is one of the most important decisions, other than cost, he must make.

For best results, the greenhouse should have full sun on three sides of the building, East, West and South. If he must drop one, make it the West side. Full sun is from 8 to 5. business hours. Ideally, the North side should be protected either with another building, the landscape, a hill or a copes of trees.

The next decision is what to build it out of. If it is a DIY, sliding glass doors are excellent as they have double panes. Storm windows will work but they will leak more. The frame may be treated lumber, metal or, best, cedar or redwood. There are clear fiberglass sheets that can be used. They need to be sealed with fiberglass cloth and will, eventually weather and become less transparent. Polycarbonate is great but expensive.

If you are going for a commercial building, they usually have all four sides clear. In Minnesota, that is not the best use of material. A kit will allow Bunkey to build with only three clear sides, thus saving the extra material to make his greenhouse a bit larger.

Kits and commercial greenhouses can be all glass, a bit tricky here in hail and strong wind country (think of flying tree branches.) Polycarbonate is a better choice. It comes in either sheets of either single, double or triple wall. The sheets look like clear corrugated cardboard. They are better at keeping the heat in the building than glass and stand up to hail. Even if they get a hit, the hail will only leave a small hole, easily repaired. Glass shatters.

Now for size. DIY, should be at least 4 ½ feet wide so you can hang grow lights in it. A cheap hack is fluorescent shop lights with one regular “blue” bulb and one kitchen/bath (pink) bulb. Hang on chains so you can move them up and down. The north side should be solid. Ideally it could be an equal sized wood building for potting and storage.

Your greenhouse will need heat. Electricity can be iffy. In a storm it can go out leaving your plants to freeze. Propane is better, however, be sure to vent it out the roof to prevent a buildup of CO in a strong wind.

Floring should be a heat sink, that is bricks, clay tile, etc. that will hold heat once heated up. it should be easy to sweep as planting is a messy job.

For your shelves, build them with a 2-inch-high edge. Fill with sand and bury a heat tape in the sand. This will help your seeds to sprout and is a backup if the heat goes out. The plant’s feet will be warm even if their leaves are cool.

Don’t buy pots! Just let your friend and neighbors know you are building a green house and need pots. Large garbage bags will appear like magic, full of plastic pots and flats. Now all you need is potting and seed starting soil and a soft rubber mat to stand on and you are in business.