How to Grow Weed in a Greenhouse
Starting a garden of any kind is a rewarding experience. Planting tiny seeds and waiting for sprouts is kind of like counting down the days until Christmas morning when you were a kid. Then, when you tend to them just right with love and care, you are rewarded with an ample harvest. Whatever you’re growing, we’re here to help with practical advice on what to grow in a greenhouse, how much it costs, and if you opt for cannabis—the best strains for your marijuana greenhouse.
What is a Greenhouse?
A greenhouse is an outdoor structure made of durable framing material covered with a transparent layer of specialized plastic. The purpose of a greenhouse is to grow fruits and vegetables, herbs, plants, and of course—marijuana.
People usually choose to use a greenhouse rather than growing outdoors because of better control over the environment. Greenhouse weed often grows faster and yields better results because the plants are protected from the natural elements, have more carbon dioxide, and have consistent temperatures.
Greenhouses are made with various materials and come in multiple styles and sizes. For example, you can make a simple hoop house with PVC pipes and painter’s plastic if you are looking for a small home grow on a budget. Or, if your space and budget allow, you can build an industrial greenhouse with automated ventilation and temperature controls and massive fan installations.
The shape of your greenhouse can be gothic, A-frame, dome, tunnel, lean-to, gable, flat-arch, and a variety of other forms to accommodate your growing needs and space availability. Wherever you place your greenhouse, make sure it receives at least six hours of sunlight every day.
What to Grow in a Greenhouse
A greenhouse is the most versatile way to grow just about any kind of plant. You can use pots of all sizes, raised beds, hanging planters, and trellises, but you can also grow directly in the ground. Greenhouses are suitable for starts that will ultimately grow outdoors in the summer months, or as a permanent home for plants to live out their life cycle.
Flowers adore the heat and humidity in a greenhouse, and even cold weather crops like lettuces, broccoli, and peas do well inside the comforts of a non-heated greenhouse. In the peak summer months watch your tomatoes, squash, and cucumber bloom rapidly in a greenhouse, but be sure to hand pollinate unless you have open-door access for pollinators to come inside.
More and more, people are building greenhouses for cannabis and producing excellent crops. Growing cannabis in a greenhouse is a perfect mixture of harnessing the sun’s power as you would in a fully outdoor environment and having the protection and control you would with an indoor grow.
How Many Cannabis Plants Can You Grow in a Greenhouse?
Each state in the U.S. has different laws and regulations regarding adult use and medical marijuana. For example, each household can grow up to four recreational plants in Oregon. If you have a medical marijuana card, you can grow six plants per patient per household. However, these numbers—and the growing requirements—vary by state.
Once you know how much you can grow, you’ll need adequate space to accommodate your growing plants. If you use high-quality marijuana fertilizer and provide your plants with optimum soil and sunshine, then you can expect some massive cannabis by the time you prepare to harvest.
Generally, it’s best to use pots inside a marijuana greenhouse so you can move them around if you need to. If you go this route, plan for at least an 8×8 foot area for each plant once it’s in its final container. Your plants need plenty of room for proper airflow. Additionally, it’s tough to work in and around overcrowded plants.
When choosing the final pot size for mature plants, you might end up on the smaller end at around 65 gallons, but some California and Oregon growers end up harvesting in 100 or 200-gallon pots.
Can You Grow Weed in a Greenhouse Year-Round?
Growing weed in a greenhouse year-round depends on where you live and what your setup is like. Properly designed marijuana greenhouses are built to sustain life in all climates. However, even locations with full winter seasons can grow in a greenhouse year-round with heating elements. In addition to heaters, you’re likely to need supplemental lighting to make up for shorter days. Although these lights do not provide enough heat to prevent frost from damaging your cannabis, they help a little bit.
However, if you live somewhere with a significant amount of snowfall, your greenhouse is susceptible to damage from the weight of falling snow on top. You can help prevent this from happening by choosing an A-frame or gothic style structure.
Items Needed to Start a Greenhouse Grow
Aside from cannabis seeds or starts, you’ll need the following items to start a greenhouse grow:
- Greenhouse framing materials
- Durable covering
- Fans / ventilation
- Smart pots or something similar
- Soil or growing medium of choice
- High-quality nutrients
- Water reservoir and access to plenty of fresh water
- pH meters and adjusters
- Trellis materials
When deciding the best time to grow weed, you might want to look into a light deprivation system. Light dep can help you maximize your output if you intend to grow more than one crop per year.
How Much Does it Cost to Start a Greenhouse
Pricing out a greenhouse is hard to nail down until you know exactly how big it needs to be. A basic DIY greenhouse with aluminum framing and one layer of polyethylene (PE) plastic is about $15-20 per square foot, not including the cost of lights, heat, or other growing materials. A custom greenhouse with all the bells and whistles (including an automated light dep system) will cost you roughly $35-40 per square foot.
If you are construction savvy and your goal is to repurpose materials and build the best greenhouse you can on a budget, you can retrofit a 1,000 square foot greenhouse for about $10,000 to include a light dep system.
Once you have your greenhouse built, you’ll need to factor in the cost of materials for each plant, including any lighting and heating equipment. Keep your calculator handy and do the math before you get started. There are plenty of costs to consider before starting your greenhouse grow.
Pros & Cons to Growing Weed in a Greenhouse
If you’ve already made your decision on whether to grow indoor vs. outdoor and have settled on the middle ground of a greenhouse, be sure to weigh the pros and cons
- Extended growing cycle and option to grow year-round
- Protection from the elements (including deer, rabbits, rodents, etc.)
- Control over a microclimate to dial in ideal plant needs
- Consistent harvests year over year
- More environmentally-friendly (and cheaper!) than growing indoors
- Depending on climate, energy costs may stack up if heating/lighting during the winter
- Odor or aesthetic may be unpleasing to neighbors
- Can easily take up a large amount of space that may have been useful for other things
- Can be expensive to build depending on the materials
- Requires more attention than an outdoor grow to ensure it’s running smoothly
If you’re ready to build your greenhouse, don’t be fooled into thinking you can guess what size you’ll need. Do a little strain research first so you know how big your plants might be when they reach full maturity. If you want to diversify your garden, leave some extra space for a few tomatoes or cucumbers and enjoy fresh produce in the summer.
Best Strains to Grow in a Greenhouse
The best strains to grow in a greenhouse are autoflower and photoperiod feminized. Autoflowering cannabis switches from the vegetative stage to the flowering stage on its own, so you don’t need to worry about the light schedule. This means that you also don’t need to worry about a light dep system. These strains include Purple Punch, Strawberry Banana, Frisian Dew, Wedding Glue, Northern Lights, and White Widow.
Photoperiod feminized seeds are another excellent option for greenhouse grows. However, they will thrive better with a light dep setup. These strains will flower naturally as the lighting changes from late summer to early fall. Some of the highest yielding greenhouse strains include Blue Dream, Sour Diesel, Super Silver Haze, Critical Kush, and Skunk XL.
Is Greenhouse Growing Right for Me?
If you are still unsure if it’s the right choice for you, ask yourself the following questions:
- Do I have the time and money to build and operate a greenhouse?
- Do I have the space to accommodate my plans?
- Does this location have easy, unlimited access to fresh water?
Starting your cannabis greenhouse is a big project that reaps plenty of rewards. Regardless of the size or strains selected, you will undoubtedly advance your cultivation knowledge and hopefully end up with some top-shelf buds.