How to Build a Greenhouse for Growing Weed (Ultimate Guide)
Last Updated: July 06, 2023By Joshua Mezher
Commercial cannabis growers and hobbyists have turned to greenhouses to grow their plants rather than warehouses or outdoor grows. Weed greenhouses are the best of both worlds- they let you grow indoors while outdoors.
If you have the money and space to set up a greenhouse for growing marijuana, you will gain a great return on your investment. Read on to find out the best way to set up a greenhouse for growing marijuana.
Growing Marijuana in a Greenhouse
Cannabis growers have traditionally grown their weed hidden in plain sight in the great outdoors or in indoor facilities. Although outdoor gardens can leverage the power of natural sunlight, you will have relatively little control over your growing environment. On the other hand, indoor growing lets you control the growing environment but does not benefit from natural sunlight and has high overhead costs.
Growing cannabis in a greenhouse combines both, allowing you to leverage natural sunlight and granting you significant control over the environment your plants grow in. Let's cover some of the main benefits of using a greenhouse rather than an outdoor or indoor grow setup to grow cannabis.
Benefits of Growing Cannabis in a Greenhouse
The following are some of the benefits associated with using weed greenhouses:
Significant energy savings - Since you won't have to rely on lighting equipment to light your plants, your energy consumption will be significantly reduced. Plus, your air conditioning system will not have to work overtime to eliminate the excess heat typically given off by lighting equipment.
Natural sunlight - Greenhouses let you leverage the power of natural sunlight for your plants. This will lead to healthier, more robust plants and significantly reduce energy consumption. Keep in mind, cannabis plants typically require up to 18 hours of sunlight per day before the flowering cycle.
Lighting control - Greenhouses grant you plenty of control over your growing environment without sacrificing the ever-important natural sunlight. You can ensure the light conditions are perfect for your plants during every stage of their development like adding lights if you plant early to keep your plants in the vegetative stage.
Climate control - Cannabis plants require a specific temperature and humidity range during their growth stages. Greenhouses allow for temperature and humidity control using a combination of paneling for airflow, air conditioners, heaters, fans, and de/humidifiers.
Disease and pest control - Outside may have plenty of natural light, but it also exposes plants to pests. However, with a greenhouse, you will be able to minimize pest problems to a significant degree.
Protection against the elements - Using a greenhouse to grow marijuana will protect your plants against heavy rains, strong winds, or other conditions that may damage the plants and hinder their development.
Superior yields - Greenhouses let you control nearly every aspect of the growing environment, including conditions and pest control. This typically leads to high-quality plants with superior potency, flavor, and aroma.
Double harvests - Greenhouses makes it easy to employ a light deprivation strategy so that you can artificially shorten the grow season which allows time for a second round of growing.
All greenhouses are not built equally. There are a wide variety of greenhouse designs, shapes, and sizes. The right type of greenhouse for you will depend on your space, the number of cannabis plants you want to grow, and your budget.
Here is a quick overview of the types of greenhouses on the market today:
Small pop-up greenhouse - This is perfect for a hobbyist cultivator who doesn't have a lot of space. It usually consists of a frame and a plastic covering. You can either buy a frame that is made to be a greenhouse or get materials cheaply from most gardening centers.
Walk-in greenhouse - This type of greenhouse is roomier and allows you to walk in and really interact with your plants as they grow and mature.
Polytunnel greenhouse - This greenhouse features a tunnel shape. It tends to be popular with commercial growers due to its size and ease to set up and work with. Polyhouse tunnels are more costly than walk-in and small-pop-up greenhouses because of the cost of materials.
Professional outdoor greenhouses - This is the top choice of greenhouses. They are usually made of rust-resistant, heavy-duty frames and extra-durable panels. Professional outdoor greenhouses are larger, sturdier, and, not surprisingly, more costly. These are almost like a combination of an indoor warehouse and a traditional greenhouse.
Consider your budget, available space, and the number of plants you want to grow before settling on a greenhouse. Make sure your available space receives plenty of sunlight and has adequate security to keep prying eyes and thieves away.
Steps to Building a Cheap DIY Greenhouse:
1. Decide how many plants you want to grow. For this example, we will be growing six plants as that is the maximum allowed in California.
2. Pick a flat space that gets a lot of sunlight, ideally 14+ hours during the peak of summer. You will want this space to be big enough to hold your greenhouse dimensions plus some extra space so that you may maneuver around and easily take care of your plants (extra important if your greenhouse is too small or too full of plants to freely move around). If it’s not flat, make it flat. If there is a slope, water will drain and pool and you’ll have one corner that turns to soup. Our 6 plants will grow in 35 gallon a Pot for Pot grow kits which are designed to grow photoperiod cannabis outdoors. We will do two rows of three pots. Each pot is 20 inches in diameter and 24.5 inches tall and the drain saucer is 22.5 inches in diameter. We want to give at least 24 inches around these pots so that the plants have space to grow out. So, the dimensions of our base will be 10 feet by 15 feet.
3. Source materials– pvc piping, stakes/posts, 2x4’s for frame/support, wire ties, 4 or 6 mil clear plastic tarp, fans, clamps, and grow kits for your weed Optional: ropes, additional lumber for frame/support, post driver, lights, blackout tarp, irrigation system, carbon filters, mulch or gravel to prevent weeds.You aren’t limited by these materials. Greenhouses, hoop houses, are simple constructions that boil down to a ribbed frame that is covered with a clear material, usually plastic. What you make your ribbed frame out of can vary, we just opted for the pvc piping because it is cheap and easy to handle. For our dimensions, we will need 4 pieces of pvc piping, 8 posts, 50 feet of lumber for the frame and 30 feet of lumber for the side support. And while our footprint is 150 square feet, our tarp will need to be much bigger to make up for the height of the tunnel and still cover the sides. So, we are going to go with a tarp that is at least double the length; 20 feet by 34 feet 6 mil clear plastic tarp.
4. Assemble the greenhouse frame. Plant posts and bend pvc piping between the posts and secure with wire (and maybe duct tape) Optionally, you can spread mulch or gravel to keep other weeds from growing. We also like to add 2 x 4’s as side support. This also makes it easy to roll up and clamp the sides during the day to get more of a breeze moving through your tunnel.
5. Pull the tarp over. (This is where ropes come in handy.) Use clamps to secure. And that’s the basics of the greenhouse!
6. Add fans, optional lights, and set up your grow kits to plant your weed seedlings and you are good to grow! Additionally, you can set up irrigation and plan for trellising in the future.
Watering and Ventilation
Once you choose a specific type of greenhouse, you need to set up ventilation and watering. Note that seedlings require more humidity than mature plants, so make sure you have an efficient hygrometer and thermometer to follow humidity levels and temperature. You will want to invest in a couple of fans to ensure there is plenty of airflow and your greenhouse has adequate ventilation. Greenhouses can trap heat and humidity too much of either and your plants will not have a good time.
To create a gentle breeze through the greenhouse, don't forget to place oscillating fans above and under the canopy.
You can also invest in an automated watering system to ensure your plants receive the right amount of water at the correct intervals. Drip irrigation systems, for instance, are perfect as they ensure plants receive the right amount of water constantly. Such a system can help you from overwatering your plants.
Additionally, make sure you have drainage and a source of water nearby.
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Lighting Requirements
During the vegetative stage, your plants will need at least 13 hours of sunlight per day. To increase growth during this stage, it is common for growers to use a light to dark ratio of 18/6. Many parts of America will need to supplement sunlight with artificial lights.
For optimal results, try to provide 400W of light per square meter for your plants. LED grow panels are a great option as they offer more than adequate light, produce little residual heat, and are quite affordable.
Just know that if you aren't planning on light depping, you may still want to consider a dark tarp for nighttime. Otherwise you may just have a giant nightlight in your backyard.
Coverings or Panels
Cannabis plants will start flowering when they receive 12 hours of light and darkness. If you plan to force the flowering stage through a method called light deprivation, invest in coverings to block out sunlight. You can use blinds, tarps, or shutters to achieve this in your weed greenhouses. But it is important that you check for light leaks. The darkness you provide your plants must be complete and total.
Here are a few more tips you can apply when you grow marijuana in a greenhouse;
Choose the correct pot sizes – a Pot for Pot offers grow kits in various sizes ranging from 0.5 gallons to 35 gallons. For growing in a greenhouse, bigger is typically better.
Consider the strain - Some strains are known to thrive in greenhouses better than others. Shop around and make sure you find a strain that meets the properties you are seeking.
Train your marijuana plants - You can use a variety of high and low-stress techniques to control the growth of your plants and direct them toward sunlight. That way, you make the most use of your available space.
Use carbon filters - Cannabis cultivation can be highly noticeable. Install carbon filters in your ventilation system to help mask the smell.
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Cultivating your cannabis in weed greenhouses has plenty of benefits. It grants you plenty of control over the growing environment and allows you to leverage the sun's power. a Pot for Pot has weed grow kits with everything you need to equip your greenhouse and grow healthy, strong, and bountiful cannabis plants.
Learn how to cultivate marijuana. Find the best marijuana growing advice for seed germination, cloning, pruning, trimming, and curing to help maximize your yields.
