Greenhouses have specific needs with temperature, lighting, and ventilation, so it’s a lot more than throwing seeds into a dirt pile. However, some basic modifications and considerations can give veggies the necessities they need to produce through Christmas and beyond. Keep the following in mind and you can build a DIY greenhouse that will make neighborhood gardeners green with envy!
According to the experts at Rodale’s Organic Life, fruit-bearing summer crops like tomatoes and peppers should hit temps between 75-85F during the day, and drop down to 60-75F at night. Cool weather crops like broccoli, peas, and leafy greens can get by with much lower temperatures, but they do best at 60-65F during the day and 50F nights. Whether you go for hot weather crops or cool climate ones, you’ll want your greenhouse to have a humidity level that’s somewhere between 70-85%.
You can use fancy growing equipment to keep your greenhouse temperatures up, but it can also be pulled off using a “passive” design. Free heat can be tapped from the sun with a passive solar greenhouse with sloped glazing to maximize sun rays. It’s very effective, albeit a bit more costly and hands-on. But, if you’re itching for a greenhouse with a penny budget, you can pull it off with a pit greenhouse like the walipini. Long story short, you dig a hole — or rather, a rectangle — that’s 6-8 feet into the ground, where temps stay around 45F all year. Top it off with polycarbonate glazing or plastic sheeting, and it’s ready for planting. For extra temperature control a la passive, use water barrels or cold sink trenches. You could be eating garden-fresh tomatoes with Christmas dinner!
Light is a must for plants, but it’s even more important with greenhouses because it doubles as a source of free heat. The best way to maximize winter UV rays is to have your glazing (ie. glass/plastic/windows) sloped at 90 degrees, so that light can be evenly distributed. You obviously want your greenhouse in a sunny location with minimal shade, but the ideal location will allow the greenhouse glazing facing south. Here, the greenhouse will have access to UV rays from sunrise to sunset. This is especially important for fruit-bearing crops like tomatoes and peppers, because they need at least 6 hours of direct sunlight to produce fruit.
Ventilation is another big player in greenhouses because it regulates temperature and keeps air fresh for healthy plants and soil. Greenhouses should be fitted with both an intake and outtake valve so that fresh air can come in, and older warmer air can be pushed out. Intake vents are best placed in the bottom half of the greenhouse for better circulation of fresh air. The top portion of the greenhouse is the ideal candidate for air outtake because it will push out the hot air that rises to the top and keep the greenhouse from getting too hot. If you want ideas on materials and tutorials on ventilation, check out the greenhouse natural ventilation guide from Greenhouse Magazine.
Thanks to old windows and Craigslist, greenhouses can be found all over the place. However, the best glazing choice for a greenhouse can vary depending on location, budget, and needs.
The trouble with glass is that it’s at risk of shattering into thousands of tiny shards — which happens all too easily with pets and children. On top of that, it doesn’t evenly distribute light, or does it take in all the shades within the color spectrum. Glass also does a pretty awful job of holding heat — a big deal the further North you live — so it’s better saved for warmer areas. However, if you’ve spotted a load of free windows online, there are always mod’s to help offset that.
Polycarbonate can offer what glass can’t by holding heat, evenly distributing light, and offering plants the red and blue tints they thrive under. Being lightweight and UV friendly, it’s a great choice for locations with short days and long nights. Quality UV polycarbonate can also last On the flip side, grooved polycarbonate allows for buildup of the 10-20 years. On the flip side, it has grooves that can trap moisture and give rise to mold. It’s also prone to scratches and gouges.
Plastic film may not have the best value, but it can get up a greenhouse in a jiffy — and for just dollars. Even though it isn’t top performer when it comes to heat, light absorption, or durability, it can keep plants alive weeks or months beyond first frost. Polyethylene film is the go-to material for tunnel greenhouses, and they’re also a prime candidate for pit greenhouses like the walipini because their design requires minimum glazing, and their pit design keeps temperatures well above frost.
If you have the yard space, then a pit-style greenhouse is really the way go to. It’s inexpensive, efficient, and outta sight; so it’s the perfect solution for the budget-minded or for newbie DIYers (or for my fellow paranoid, survivalist, apocalypse preparers). The catch with the pit greenhouse is that you have to dig at least six feet down. This can be pulled off with a shovel, but that kind of job is best saved for a work crew or die hard penny pinchers with hours and hours to spare. You can build a walipini in a jiffy by using earthmoving equipment like mini excavators. Check out Craigslist or look for local construction equipment companies to help you out. If you’re renting, it’ll cost you a couple hundred, but that’s still way less time and money than it would take to plan, frame, wall, and trick-out a greenhouse on the ground.
Article written by Ash Stevens, blogger over at One Damn Good Woman. Ash is a mother, writer, and a wannabe shaman. She loves health, gardening, simplicity,culture, chocolate, and sarcasm. If she isn’t writing about family and relationships on her blog, then she’s surely playing badminton with the kids. Find her on Twitter or Facebook and make a new friend!