How to Start Growing Cannabis in a Greenhouse

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Cannabis Plants in Greenhouse
Author avatar By Parker Curtis
August 30, 2021
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Perhaps you’ve just harvested your first batch of weed, and you’re seeking a way to bump up your yields. Maybe you have a few outdoor plants that aren’t doing well or, you’d simply like to grow your favorite strain year-round. Either way, growing cannabis in a greenhouse may well be the next move to stepping your weed game up.

Setting up a greenhouse for your next marijuana crop might seem like a huge endeavor, from setup and running costs to the actual day-to-day maintenance and care. 

Simply put, you’re creating ideal conditions for your plants by using a greenhouse, and you might find that you’re rewarded in many fantastic ways if you choose this path.

Let’s dig in as we learn more about the hows and whys of growing cannabis in a greenhouse.

How does a greenhouse work?

Greenhouses are excellent tools that have the potential to boost cannabis crop production. They allow you to grow bumper crops year-round, regardless of the weather conditions. 

If managed correctly, you can get a grip on pests in your marijuana greenhouse, protecting your plants. You may even find that you’re saving on general overheads and utility bills.

Remember that, while the sizes and options vary, the aim is to produce the ideal conditions for your plants. The sealed environment provides optimal temperature and humidity conditions from seedling or cutting stage to harvest.

Sea of Green Cannabis in a Greenhouse
Sea of Green Cannabis in a Greenhouse

Why start growing cannabis in a greenhouse?

There are a whole host of reasons to start a marijuana greenhouse of your own, ranging from space constraints to odor control (not everyone may share your love for the smell of dank indica in their homes year-round) and improved lighting conditions. 

You’re also able to dictate when your plant comes out of vegetation and moves into bloom.

By employing solar power systems, you could run your setup completely off-grid, albeit at a higher initial investment.

Safety

You may have experience with growing plants indoors, possibly stemming from a mishap due to the uncontrolled outdoor environment. 

Many potential hazards face a weed crop, from forgetting to switch off your lights to skipping a watering day.

An adequately managed cannabis greenhouse grants you some forgiveness for minor oversights, as your plants will already be much happier and healthier in general. Through automating specific tasks, like watering, lighting, and even fertilization, you’ll add an extra layer of safety for your plants.

PVC Plastic Tunnel Greenhouse
PVC Plastic Tunnel Greenhouse

Light Control

One of the perks of growing cannabis in a greenhouse is that you get to take advantage of the best light source available, the sun itself! 

While technology has made great strides from the old fluorescent tubes to new HIDs and LED setups, nothing beats the price-to-performance ratio of our very own daystar.

On cloudy days, you can supplement what nature is already providing. If you’re moving from an indoor setup, the energy savings are palpable nearly immediately. You can accurately mimic night-time conditions through the use of a sailor black-out curtain over your cannabis greenhouse.

Climate Control

While most people consider weed as a relatively robust crop, there are innumerable benefits to keeping it in a controlled environment

Simply put, 70 degrees Fahrenheit is the sweet spot, and a variance of 20 degrees in either direction could be the difference between a bumper crop and utter disappointment. 

Regardless of where you find yourself, through the correct usage of design and technology, you can regulate the temperature of your weed greenhouse perfectly. Humidifiers, fans, and cold walls allow you to compensate for nearly all adverse weather conditions and keep your plants comfortable, even when you’re not.

Conserve Energy 

You may consider a separate structure outside of your home, requiring lighting, irrigation, and temperature regulation, as a substantial additional monthly expense. 

While you may not be wrong, there are numerous ways to offset the costs involved, with intelligent design and material choices like solar panel arrays. 

Life Cycle Control

This may be the driving force behind dedicated cultivators choosing to set up an outdoor marijuana greenhouse. You can grow excellent crops year-round, and when you’re ready, flip the switch and start the flowering process at the perfect time to harvest. 

Perhaps your region experiences icy winters, and you don’t plan on growing year-round or running the expenses of climate control through this period. Simply start cutting the amount of lighting your crop receives and trick it into flowering early

This way, you can harvest well before the cold sets in and have your cannabis greenhouse ready for the next batch of seedlings when the worst has passed.

How to start growing marijuana in a greenhouse

As with any functional structure, there’s far more that goes into it than simply providing a roof and four walls. There are a few additional requirements for growing cannabis in greenhouses.  

Let’s take a look at some of the furnishings you’ll need to make your greenhouse an ideal home for your plants.

Growing Weed in a Greenhouse

1. Choose Your Equipment 

You may find that one of the most significant aspects of learning how to build a marijuana greenhouse is the excellent level of scalability.

As with the enclosure’s size, you can find a balance that suits your needs and budget through research and practical application.

1.1. Heating

One of the most significant benefits of growing cannabis in greenhouses is that they’re warmer during the day by nature. Depending on your chosen construction materials, you may find that you need to provide heating artificially during the colder months. 

If you have a large enough cannabis greenhouse, an easy natural way to heat the space is to start a compost pile right in the middle of it. While the smell may be something to get used to, you’d be surprised at the amount of energy it radiates.

Depending on the size of your marijuana greenhouse, you may be able to install a space heater like those for garages or workshops. Make sure you have enough fans to circulate the air and eliminate cold spots.

1.2. Lighting

Getting back to the benefits of having an outdoor setup, you want at least 6 hours of full-spectrum lighting as provided by the sun per day. You might find that in the summer months, you can get away with hardly any supplemental lighting at all. 

For most outdoor marijuana greenhouse owners, lighting may prove to be the most significant contributor to running costs

HPS solutions enjoyed a fair amount of time in the limelight as the choice option for full-spectrum artificial lighting. Their scalability in wattage, reasonable energy efficiency, and cost-per-watt are all considered great reasons to buy. The heat they radiate may also prove beneficial during colder periods.

LED lighting is gaining ground at a rapid pace as the go-to solution for new setups. The efficiency is undeniable, with some implementers claiming up to a 75% energy saving after moving to an LED solution

LED arrays also allow you to precisely dial in the color spectrum. The only downside is that LEDs generate less heat due to their design efficiency.

Weed Plants in a Greenhouse

1.3. Ventilation and Fans

Fresh air circulation is essential when growing cannabis in a greenhouse. While some designs may allow natural cross-ventilation, you need to consider fans and ducts to channel air throughout your greenhouse

Remember that you may want to “seal” the greenhouse altogether in colder months and pollen season to prevent heat from escaping or contaminants from entering. To this end, many choose to invest in at least a fine screen covering for vent openings. 

2. Choose Top-Quality Soil

Once it’s time to start planting, make sure you invest in the best soil you can get. Just as you built your greenhouse for marijuana on a prepared base, you want your cannabis to grow from the strongest foundation you can give it. 

There are hundreds of options in this sector, but generally, you’re looking for loamy soil that offers excellent water and nutrient retention without draining too slowly. You can also add coconut coir, perlite, and vermiculite to get the mix just right if you like to prepare your own.

3. Do Your Research

Our best advice before you do anything is to research. Some states may require a building permit before you’re even allowed to begin constructing a greenhouse. You may have to obscure the greenhouse’s visibility or not grow outdoors at all in other states.

Seek out online forums that deal with greenhouse keeping (not only for marijuana-specific purposes) as you’ll find the experiences of a broader user base rather than simply going on what one website wants you to believe.

As with any new endeavor, ample research will save you many potential hassles, legal issues, and ultimately money. 

Building your own greenhouse for marijuana

You’re probably familiar with the images of agricultural greenhouses, from the vintage timber and glass structures to modern polytunnels lined up in farm country.

As with most things, you may seek the best value you can get your hands on. Maybe you’re flush with cash, and you’re looking for the very best setup money can buy. Whatever the case may be, this begs the question; what are the best materials to use when constructing your outdoor marijuana greenhouse?

Glass

Perhaps the original go-to material for greenhouse construction and still a popular choice. Many may argue that glass is the way to go for a greenhouse that could very well last you the rest of your life. A well-designed glass greenhouse for marijuana will also add to the appeal and value of your property.

While it may arguably have the highest initial cost, glass stays clear for far longer than plastics or polycarbonates as it’s inert. 

It’s also non-combustible and, with regular cleaning, allows excellent radiation transmission throughout its lifetime, remaining beautiful long after plastics have grown brittle from sun damage.

Aside from the initial cost of more robust structural requirements, you also need to consider that glass is prone to catastrophic failure due to hail or even earthquakes. While you could factor these into your original design specs, they’ll inevitably add to the set-up cost. 

The need for sturdy foundations and framework also means that most glass marijuana greenhouses are a pain to relocate.

Parker in HMG Greenhouse
Parker Curtis in Homegrown’s Greenhouse

Fiberglass 

Corrugated fiberglass is an excellent and cost-saving choice when it comes to setting up a greenhouse quickly. It’s the ideal material for a beginner without any crazy equipment requirements, from simply cladding a timber frame to ordering DIY kits online. 

The high level of rigidity is excellent for wind, hail, and also heavy snow protection. It’s near effortless to work with, light, and offers excellent insulation properties

Compared to glass, it’s pretty easy to cut, bend and drill to your requirements without the risk of breaking and causing injury. 

Once again, quality is directly related to cost. Some manufacturers offer fiberglass that may stay clear and flexible for up to twenty years, while cheaper fiberglass marijuana greenhouses may start yellowing after less than four years. Fiberglass is also highly flammable, which should also be a design consideration.

Plastic

The material of the future! Plastic products are rapidly moving into a preferred material for commercial cannabis greenhouses the world over. There are many reasons for this, from cost savings to safety and ease of setup.

Generally, there are two different branches people refer to when talking about plastics. The one is the line of more rigid polycarbonate products, and the other would be the flexible, skin-like films. Some people like to use a combination of the two to reap the benefits of each. 

A polycarbonate roof allows excellent light diffusion, while plastic films provide cheap but effective walls. Polycarbonate is also a perfect option for a stealth outdoor grow solution where neighbors are a concern.

While you could get away with a cheap plastic-clad frame as a temporary solution, your investment has a direct impact on the longevity of the structure. Bear in mind that your design needs to compensate for potential adverse weather conditions as well.

HMG Garden Greenhouse
Homegrown’s Greenhouse

Buying a marijuana greenhouse

The idea of building your greenhouse from scratch might not appeal to everyone. You’re probably here to grow, not to build, right? 

Enter the world of prefabricated marijuana greenhouses. Everything should be pre-cut, measured, and supplied to order, taking the guesswork and frustration out of the DIY process.

Polytunnel 

Generally constructed out of steel hoops that are then tightly covered in clear or diffused plastic sheeting, cannabis polytunnels offer excellent value for money and simplicity. They’re usually placed directly on a soil base, which requires minimal ground preparation.

High ceilings also mean you can walk around comfortably all day long without developing a creak in your neck. If you pick a model with a high enough peak, you can also raise your plants, saving your back and knees too.

They’re also easy to pack up and move, should you ever find the need to relocate

Let’s give you an idea of what longevity to expect; the galvanized steel frame could very well last up to 20 years. You should budget that you may need to replace the polythene sheeting on your marijuana polytunnel at least once in that lifetime.

Cold Frames

Cold frames are a great starting place for someone on the fence about investing in a full greenhouse setup. Think of these as mini ganja shelters with just enough space for your crops.

You’ll have the benefits of being able to completely cover your plants to protect them from the elements and require a tiny initial investment. This also marks the second-lowest level of environmental control you’ll be able to offer your plants. 

Cold frames mark a sort-of middle ground between an indoor marijuana setup and simply exposing your plants to nature completely

You’ll have the benefits of the sun as well as moisture retention. Most of the other functions will fall squarely upon you, though, making this potentially much more laborious than a greenhouse or a tunnel solution.

Parker Watering Plants in Greenhouse
Parker Watering Plants in the Greenhouse

Choosing the best marijuana greenhouse location

There are many things to consider when choosing where to build your outdoor marijuana greenhouse. In some cases, regulations may dictate your options (that suspicious gazebo on the front lawn might not go down well with the neighbors anyway.)

Generally speaking, you want a spot that gets the most sunlight every day, year-round, ideally from the early morning. 

Many growers use a south-facing location for this reason. Ultimately, this becomes a combination of convenience, practicality, and what works best for the plants. You are, of course, pursuing this endeavor because you’d like to see your cannabis flourish.

Growing cannabis in a greenhouse: is it for everyone?

While it would be easy to shout a resounding “yes” and call it a day, be sure to get some insights into what people’s time investments are when growing cannabis in a greenhouse.

If you’re looking to increase your yields and grow the best buds you can imagine; a marijuana greenhouse is an obvious choice.

Over the long term, if done correctly, you may begin saving money.

As with much in life, you may save yourself time by investing in automation systems and sensors. Likewise, you’ll be able to save money if you’re willing to spend more hours tending to each plant and checking each parameter yourself. 

The experience of learning growing cannabis in a greenhouse is a reward in itself. 

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About the author: Parker Curtis

Parker Curtis has around a decade of cannabis-growing experience, specialising in soil-less and hydro grows. He’s mastering outdoor, greenhouse, and indoor grows.