When you grow marijuana outdoors, your plants are at the mercy of the elements. If you live in a climate with inclement or unpredictable weather conditions, your plants are at risk. A sudden frost could kill your crop overnight. Meanwhile, high winds and heavy rain could also cause havoc. With a greenhouse, you retain control over temperature and humidity.
Adjusting your watering schedule is important to ensure there are no humidity issues. Outdoor growers should avoid their typical watering habits. Water evaporates from the soil much faster outdoors than in a greenhouse. As a result, watering plants as you would outdoors will lead to overwatering.
When choosing a site for your greenhouse, make sure it matches the dimensions of the grow space available. Remember, you also need some free space to move around inside the building. Finally, set it up in the part of your garden that gets the most sunlight.
Likewise, a simple oscillating stand fan gently blowing air across your plants can prevent pockets of stagnant, humid air from forming. You should also keep a thermometer and hygrometer in your greenhouse. Just keep an eye on these things and your cannabis will thrive!
As such, you want to make sure that your greenhouse has optimal ventilation and cooling, and you may want to consider artificial lighting with less heat output, like LEDs.
Supplemental grow lights aren’t just good for greenhouse growers in regions without much sun; they can be beneficial for growers in any location. Even in sunny climates, an additional grow light can get your plants through the cloudy days. Plus, if you live somewhere with a chilly climate, a powerful HPS light can support adequate temperatures for your plants.
Another big benefit of having a grow light in your greenhouse is that you can extend the hours of light your plants receive. For example, you can use the lights to provide your vegging photoperiod plants with 18–20 hours of light, even when natural daylight hours would be much shorter. This allows you to grow your plants all year long—plus it will greatly increase your yield.
CONSIDER HEAT AND HUMIDITY WHEN BUILDING YOUR GREENHOUSE
Where you place your greenhouse is very important, for a number of reasons:
The location of your greenhouse will ultimately determine how much sun your plants receive. Obviously, you don’t want to place your greenhouse behind your house in the northern part of your garden where your plants never get any sun. The best location is the south or southeast side of your house.
When growing feminized photoperiod strains, you have the choice to use exclusively natural sunlight, or you can supplement with artificial light. If you grow in natural sunlight only, your plants will essentially have to follow the regular outdoor grow season schedule. At the end of summer, plants will start to flower, and then you can harvest sometime in autumn. Luckily, the controlled conditions of a greenhouse can support flowering deeper into fall, which is a major benefit for sativa growers especially.
EARLY FLOWERING WITH AN AUTOMATED DARKENING SYSTEM
Given ideal environmental conditions are met, your plants can, in principle, grow just as large in a greenhouse as they can outdoors. It’s not uncommon for cultivators to harvest 2–3m-tall monsters, or even taller. Of course, this all depends on how much space you have in your greenhouse and how large of a plant you want to deal with. Even if you don’t have a super tall space, you can still potentially grow sativas and other lanky strains using training techniques. Simple LST can keep vertical growth in check, and techniques like topping can help to boost yield while breaking apical dominance. You can also keep height in check by skipping the vegetative phase and initiating flowering right away.
The ideal spot for your DIY grow room will be facing the sun. A slightly shaded area is fine, but make sure nothing is keeping the natural light from reaching your greenhouse. The more hours of light, the bigger the yield.
Free-standing greenhouses: From a simple walk-in greenhouse with room for a couple of plants to the massive connected behemoths set up by commercial growers, free-standing greenhouses are what most people picture when they think of a greenhouse. They are apex shaped, like a house, and consist of metal or wood frames and glass, fiberglass, or plastic panels. Many have roof and/or side panels that open to allow for ventilation. This may be the most expensive option, but it also has the most room for plants while still allowing for location flexibility so growers can move it to best capture the sunlight. Inexpensive free-standing models start at less than $100 but they may not be very durable. Sturdier models cost closer to $1,000 and prices go up from there.
Building a cannabis greenhouse
Knowledge: The most high-tech equipment won’t matter unless you have a thorough foundation in how to grow cannabis. This means understanding when seeds should be sown (generally April), when flowering occurs (eight to 12 weeks typically), and which cannabis strains do best in greenhouses (autoflowering strains such as Purple Punch Auto, Jack Herer, and 8-Ball Kush enjoy a great reputation among cannabis growers).
A marijuana greenhouse also puts you in control of two primary factors in successfully growing marijuana plants.
Buying a cannabis greenhouse
Cold frames: Cold frames are another affordable choice, though they are small and temporary. While it’s possible to construct a cold frame yourself, you can purchase a solid one for between $80 and $200, depending on the size. Cold frames are generally small boxes that sit on the ground. They are constructed out of wood or plastic frames with plastic or glass panels. Cold frames are normally used as is, with only heat from the sun, especially in warm, dry climates like Southern California. In areas with colder temperatures, consider installing a heating system, also known as a hotbed.