March 26, 2020
How to Build a Cannabis Greenhouse in Your Backyard
You’ve been thinking about growing cannabis but the idea of growing indoors, without the sun, seems absurd. On the other hand, you’re pretty sure the unpredictability of Mother Nature will give you an ulcer. You also have nosy neighbors who might gasp at the sight and smell of cannabis. What to do?
A greenhouse might be the solution. Greenhouse agriculture is an effective way to produce high quality, high yield cannabis with a minimal carbon footprint. When properly cured, greenhouse cannabis can last more than a year.
Estimate Space for Full-Grown Plants
It’s not uncommon for cannabis plants to become six-foot giants or bigger. “If you want a monster-size plant with big yields, make sure you account for that in your greenhouse design. 12 feet at the apex of your greenhouse may not be enough,” says Stefani Malott of Phyre Farms.
You can also plant one row down the middle to avoid plants touching plastic. Michael Lupario of Western MA Hemp in Massachusetts warns: Too little headspace may cause the plant to touch the roof and condensation will do the same kind of damage as rain. Adjust the dimensions accordingly.
Consult Your Local Building Department
Find out what local permits may be required for your greenhouse. If your structure will have electricity, you will likely need a permit!
Plan, Plan, Plan
Plan for harvest before you even start planting. Many growers work hard to produce the best possible crop through the growing season, only to have it ruined come harvest time. Major culprits: lack of labor and inadequate curing space.
You can’t dry and cure in your greenhouse because the conditions required for the two operations are incompatible. Be sure you have a separate space for all your harvested buds.
Expect to spend between $300-400 dollars, depending on complexity and size. If you can reclaim old materials it’ll be even cheaper. Cost estimates are based on a hoop house of 12’ H x 12’ W x 12’ L, which can comfortably fit 6 cannabis plants.
- Wood—cedar recommended—for base boards, 6 2’x4’s: ~$60
- 6 Rebar stakes, ½” diameter, 2’ length: ~$20
- Rubber mallet: ~$5
- PVC pipes:
3 at 1 ½” diameter, 20’ long: ~$60
3 at 1 ½” diameter, 12’ long: ~$30
- Plastic sheeting, 6 mil polyethylene, 24’ x 20’: ~$100
- Stapler and staples: ~$10
- Duct tape: ~$5
- (Optional) Landscaping fabric as shade cloth for a light deprivation setup: ~$10
Step By Step Guide to your Greenhouse
- Find a level plot of land about 12 feet wide and 12 feet long. Make sure it faces south, where sunlight will be coming from throughout most of the day. It should not get any shade nor have any light obstruction from buildings nearby. Make sure the land has good drainage. Get rid of weeds.
- With a measuring tool, mark the corners of your plot.
- Build a rectangular frame with the wood boards over your site. Check to make sure the frame is squared up. This frame will add extra support to your entire structure.
- Using a mallet, pound the rebar stakes halfway (1’ deep) into the ground, at each corner and in the middle of the sides (6’ intervals for bigger structures).
- Slip one end of a 20’ long PVC pipe over a rebar stake, bend it, and put the other end of the PVC pipe over the rebar stake on the opposite side.
-Repeat with the other 20’ long PVC pipes.
- Add the spine—connect each arch to one of the 12’ PVC pipes at the topmost point of each arch. Attach with duct tape.
- Take another 12’ PVC pipe (this is a crossbar) and tape it to the arches about halfway between the ground and the spine, or 5-6’ from the ground. In a bigger, sturdier structure, you can use wood and these are called hip boards.
- Attach the second crossbar to the other side.
- It’s time to put on the plastic. This step ideally requires three people. Do it on a warm day so the plastic can stretch.
- Lay the polyethylene sheet appropriately over the structure and staple it to the base boards. The plastic should be tight enough to prevent sags or billowing when air goes through it.
- Leave some plastic on the ends like a curtain, so you can clamp it closed or lift it as needed for ventilation.