To set up a cannabis greenhouse, pick a structure that fits your space and budget, then nail three things: ventilation and humidity control, a watering system that won't drown your plants, and a way to block light if you want to force flowering. Done right, a greenhouse protects your plants from cold and bad weather and lets you get the most out of the sun. The cool thing about growing is that there's more than one way to do it, so here's what you need to build one at home.

What Is a Greenhouse?

A greenhouse is a structure that creates an ideal microclimate for plants. You can use it to grow plants or to house them for their whole life, which makes it a big project to take on. That said, you can build one on a tight budget or leave it to professional builders.

Why Grow Cannabis in a Greenhouse?

The main advantages of a cannabis greenhouse include:

• Lower energy use: growing in a greenhouse lets you use sunlight instead of paying for a grow light running 18 hours a day.
• Control over growing conditions: in an outdoor grow, plants are completely exposed to the elements. A greenhouse, on the other hand, gives you much more control over your plants' environment, so you can dial in temperature, airflow, humidity and more.
• Better potency, aroma and flavor: results vary a lot depending on the strain and your skills as a grower, but greenhouse weed has earned a solid reputation for potency, aroma and flavor, probably thanks to the control this setup gives growers over the quality of their harvest.
• Better pest control: outdoor cannabis is exposed to pests that are hard to control and get rid of. In a greenhouse, though, you can cut the risk of pests way down, much like in an indoor grow.

How to Build a Greenhouse for Growing Cannabis

Like we said, building a greenhouse isn't easy, and there are a ton of variables that depend on your situation (how much space you have, the materials you can get, your budget, your DIY skills and so on). Here we'll cover three things: the types of greenhouse, how to set one up, and the key things to keep in mind once it's running.

Types of Greenhouses for Growing Weed

The great thing about greenhouses is that they come in all kinds of shapes, sizes and designs. Which one you go with depends on your budget, how many plants you plan to grow and how much space you've got.

Here are some of the types of greenhouse you'll find on the market:

• Small pop-up greenhouses: these are the most affordable and are usually aimed at hobby gardeners with limited space. They come with a frame, a plastic cover, a few shelves for plants and tools, and a zip-up door for easy access. This is the cheapest option out there.
• Medium walk-in greenhouses: usually also made with metal frames and plastic covers, these give you a lot more room, bigger shelves and the chance to step inside and really get into caring for your plants. They come in several sizes and styles and suit people with a bit more space (a backyard, patio, deck or garden). Prices vary a lot, but they tend to cost more.
• Hoop houses (Quonset greenhouses): these are tunnel-shaped and among the best known and most popular in commercial growing. Because of their size, they're built to be used outdoors and are better made as a result.
• Professional outdoor greenhouses: these are easy to spot by their size, build quality and price. They're usually made with rust-proof aluminum frames and very durable polycarbonate panels, which offer maximum light transmission and protection from the elements. Along with hoop houses, they're the priciest on the market.

Key Tips for Growing Weed in a Greenhouse

Keep humidity down: set up ventilation and watering

One of the biggest problems when growing cannabis in a greenhouse is high humidity. Those humid conditions are great for seedlings, but they're a big problem for mature plants, because they create a breeding ground for bacteria, fungi and pests.

To keep it in check, use a thermometer and a hygrometer to monitor temperature and relative humidity inside the greenhouse.

It's also worth investing in intake fans, oscillating fans and exhaust fans to give your plants plenty of fresh air and keep temperature and humidity down.

The best kind of fan depends entirely on the size of your greenhouse. What you're after is a gentle but steady breeze moving through the whole space.

Automatic watering systems

To keep moisture problems from hurting your harvest, use a proper watering schedule. Investing in an automated watering system is a great way to head off trouble.

Drip irrigation is a good choice, since it gives your plants just the right amount of water with no excess (which in turn lowers the risk of bacterial and fungal problems), and it encourages healthy roots and much more.

If you've been growing outdoors, don't just carry over the same watering routine, or you could end up overwatering your plants.

Cover the greenhouse (to force flowering)

A greenhouse works the same way as any other grow when it comes to flowering. Cannabis naturally starts to flower after the summer solstice, as the days get shorter and fall and winter approach. In a greenhouse, though, you've got two options for flowering:

1. You can let the plants grow the way they would in nature and wait for them to flower as the light cycle changes after the summer solstice. This is the simple route and just takes a little patience.
2. Or you can put blackout blinds or covers on the greenhouse to block light and force flowering (a technique known as light deprivation, similar to what you'd do in an indoor grow room). As you'd guess, it's more work, but it gives you more control over your plants and how they develop.

A few ways to force flowering in a cannabis greenhouse:

• Use a tarp: get a custom-fit black tarp that goes over the outside of your greenhouse and pull it on and off by hand to cut down how much light your plants get each day. Fair to say it's the easiest, cheapest fix if you've got a small greenhouse.
• Use curtains: hang them along the inside walls of the greenhouse and cover the roof with a tarp.
• Install blinds: one of the easiest options but also the most expensive, since automatic blinds let you block out the sun at the push of a button.

Tips for Setting Up a Cannabis Greenhouse

• Know your strains: when you start planning your greenhouse, get to know the strains you're going to grow. Ideally, pick strains with the traits you're after that have a track record of doing well in a greenhouse.
• Know your space: take the time to think through how much room you have in the greenhouse and how you'll divide it to give your plants the best environment.
• Use the right size containers: in a cannabis greenhouse, plant size matters. For medium-sized plants, we recommend 2 to 4 plants per m² (about 11 sq ft) in 12–15 L (3–4 gal) containers. That way each plant has room to grow, and they're easier for you to tend.
• Train your plants: there are different techniques you can use, even combined, especially low stress and high stress training, to control how your plants grow and make sure they make the most of the available light and space.
• Keep a faucet and a drain nearby: make sure you have access to water inside or near the greenhouse, plus somewhere for it to drain.
• Plan everything ahead: whether you buy a greenhouse or build it yourself, you need a solid plan. Factor in the size and shape of the greenhouse, how many plants you want to grow, the materials you'll use (if you're going DIY) and the day-to-day logistics of the grow (watering, feeding, training and pruning, etc.).
• Don't forget carbon filters: if you're growing more than a handful of plants, add carbon filters to your ventilation system to mask the smell of cannabis.

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