How to grow cannabis in a greenhouse

How to grow cannabis in a greenhouse
Steven Voser

You may have seen tomatoes thriving in greenhouses and wondered, can you grow cannabis in a greenhouse too? The answer is yes, you can! And not only does it work, but plants will thrive under the right circumstances. Taking the benefits of both indoor and outdoor growing, discover what you need to know about cultivating cannabis in a greenhouse.

Some people love the control of growing cannabis indoors, while others think that growing weed outdoors in its natural habitat yields the best results. How do you decide? Well, why not harness the benefits of both and grow in a greenhouse?

Simple, cheap, and highly effective, growing in a greenhouse is a fabulous option for cannabis growers of all stripes. Stick with us as we break down the what, why, and how of greenhouse growing.

What Is Greenhouse Cannabis?

How to grow cannabis in a greenhouse

Growing cannabis in a greenhouse provides the best of both indoor and outdoor growing. Greenhouse growers benefit from natural sunlight—which, when ample and bright, cannot be beaten—and the highly controlled environment offered by indoor growing.

With this in mind, greenhouse cannabis can rival the yields of a bushy outdoor grow and the quality and density of an indoor grow!

Why Should You Grow Cannabis in a Greenhouse

How to grow cannabis in a greenhouse

Cultivating cannabis in greenhouses is growing (pardon the pun) ever-more popular, and with good reason. The pros of greenhouse growing include:

  • Can grow all year round (with supplemental lighting)
  • High degree of control
  • Avoids the need for pesticides
  • Perfect microclimate
  • Consistent, predictable harvests
  • More energy efficient
  • Protection from undesirable elements
  • Allows for covert growing while retaining large plants and ample crops
  • Cheap!

How To Grow Cannabis in a Greenhouse

How to grow cannabis in a greenhouse

While growing in a greenhouse is fairly simple, there are some unique aspects you need to account for if you want to get the full benefit of a greenhouse grow.

Buy or Build a Greenhouse?

You may already have a greenhouse, or even a large polytunnel just waiting for a new crop of weed to fill it. But if you don’t, you’ll need to source one somehow. Is it best to buy a greenhouse, or build your own?

The answer to this comes down to a few variables, not least of which include your budget and your ability to build one well.

Building your own can be cheap and a fun project. Growing your own weed inside a greenhouse you built yourself can be highly satisfying. On the other hand, they can be big structures and—if you need to rig lights—might need to be fairly robust. So it will require some effort and handiwork on your part.

Depending on the size, buying one can range from very affordable to pretty expensive. But it will be a fairly painless experience, and (hopefully) will be of high quality.

In any case, the considerations that will dictate the form your greenhouse takes are:

  • Size of grow
  • Location
  • Whether it needs to open fully
  • Whether you need to cover it (providing darkness)
  • Whether you want to get inside it completely
  • Whether you need to rig lights

So, whether you’re buying or building a greenhouse, accounting for these needs is important. Ultimately, the choice mainly comes down to size. It needs to be big enough for your needs, but small enough to fit. All going well, your plants will grow vigorously, so give them enough space!

The Importance of Location

When choosing a location for your greenhouse, there are a couple of factors to consider. First, how many hours of light will your plants be exposed to? Greenhouse growing is all about utilising the natural power of the sun, so a patch that’s in the shade for half the day won’t cut it. Ideally, you want it to get direct sunlight from dawn till dusk. At the very least, plants need 12 hours of light to flourish.

Second, depending on where you are, security will be a consideration. In most places, blatantly growing cannabis might not go down so well (sadly), so somewhere with a bit of subtlety is probably helpful. It might be worth putting a padlock on the door, too.

Choose Your Growing Setup

Hydro or soil? A greenhouse can provide the perfect environment for either type of setup, so the choice is yours.

Soil is simple and easy. By growing in pots, soil greenhouse grows will flourish, producing massive, healthy plants.

On the other hand, why not try your hand at a hydro grow? Hydro will give you a slightly shorter grow cycle and, if it goes well, allows you to eke every last gram of THC out of your cannabis plants. On the other hand, it is a more involved process, and any problems that do occur are harder to rectify.

Pick the Right Strain

Anyone who’s grown weed before knows that the myriad strains available don’t just produce different flavours and highs, but have their own special needs when growing. Ranging from tough and resilient plants to divas who will drop dead at the first sign of a nutrient imbalance, picking the right strain can make the difference between a successful grow and a failed one.

Should you go for an autoflowering strain or a photoperiod? Besides yield, taking growing characteristics into account will help you decide. Fortunately, both can be grown with equal success in a greenhouse, but the experiences will be different.

The pros of growing autos include:

  • Great resilience (due to hardy ruderalis genetics)
  • Ability to grow year round, as they work on any light schedule
  • Speedier life cycle means you can fit more grows in
  • Smaller size can be more suitable for small spaces and techniques like SOG

The pros of growing photoperiods strains are:

  • Bigger plants and bigger yields (this is a pro and a con; they will need to be controlled)
  • The grower (or the season) controls when plants move into bloom, allowing you to extend the veg phase if needed

Though every grower has their favourites, our top strain recommendations for greenhouse growing are:

  • White Widow: This strain copes with environmental changes, responds well to training, and delivers up to 600g/m² in a greenhouse.
  • Northern Lights: A classic strain, NL is easy to grow and offers big yields, good pest and rot resistance, and a renowned relaxing high.

Plan the Grow Window

As you’ll be relying either entirely or primarily on natural sunlight, you’ll want to plan your grow to start in the spring. The earlier the better, as it gives photoperiod plants maximum time to veg and increase their size, and means auto growers can cram an extra crop in.

Thanks to the extra warmth of a greenhouse, you can start growing as soon as the last frost is over.

Germinating Indoors

To make the very most of available days, you can germinate your cannabis seeds indoors beneath CFL lights, and then move them into the greenhouse once they enter the veg stage.

While this maximises all of the resources at hand, you’ll need to introduce them to their new environment with care. Although a greenhouse provides more control than growing outdoors, the transition to a perfectly stable indoor environment could still be a shock to young plants.

Introduce them a few hours at a time at first, extending their stays in the greenhouse over a week or two. This way, you’ll avoid causing them harm through stress and shock. Autoflowering strains are particularly bad at recovering from early stresses, as they grow so fast.

Add Lighting

Of course, one of the best things about growing in a greenhouse is that you rely on the sun for your light. Nevertheless, stretches of poor weather, or the desire to grow outside of the normal growing season, demand supplemental lighting. Fortunately, greenhouses provide an environment in which you can set up artificial light systems, but run them at a much lower cost than indoors.

Ensuring ample lighting for your cannabis plants means you'll get the very most out of them, and that you can potentially grow year round in your greenhouse, using the sun when it's available.

Create a Darkening System

All things love balance, and cannabis is no different. Giving your plants enough darkness is as important to their health and your harvest as light is. Therefore, you might need to create a darkening system. Maybe you want to force flowering early, or perhaps you need to make up for the unwanted light provided by a streetlight at night. Either way, light deprivation can be a useful tool in the grower’s arsenal.

If you have the budget and the structure, you can set up electronic blinds on a timer and do it this way. Most amateur greenhouse growers, however, tend to find that some manual blinds or even an opaque tarpaulin thrown over the top of the greenhouse does the job just as well, for almost no cost (and less opportunity to go wrong).

Growing Cannabis in a Greenhouse: Extra Tips

Create a darkening system

There’s a lot more to a marijauna greenhouse grow, and much of it is the same across the different grow systems. Here are our top tips for getting your greenhouse up and running and capable of delivering a superior crop!

  • Airflow: Greenhouses get humid, and fungus loves humid environments. Either by opening the sides or installing a fan, keep the air moving around your greenhouse to prevent mould taking hold.
  • Temperature: The massive benefit of a greenhouse is that it holds heat. But in summer, things can get too hot. Keep an eye on the temperature and be ready to throw on the covers when the sun gets too intense.
  • Training methods: SOG and ScrOG will help you make the very most of the space available to you, maximising your overall yield.
  • Watering: Depending on your setup—pots, soil bed, hydro—your watering regimen will vary. If you’re new to growing, the thing to watch out for is overwatering your plants, not underwatering.
  • Cleaning: Weed is not the only thing that thrives in the hot, humid, and well-lit environment of a greenhouse. A regular cleaning regime is essential to stop infestations taking hold in this most hospitable of environments.
  • Security: Even when padlocked, greenhouses are easy to see into and get into, so be aware of this factor when growing in them. However, they tend to be more secure than outdoor grows.

Growing Greenhouse Cannabis: Good Luck!

Create a darkening system

You’re now ready to take full advantage of growing cannabis in a greenhouse! Boasting the vigorous growth of outdoor plants and the high-quality buds of indoor plants, greenhouses have a lot going for them. Combine that with the highly controlled environment and no-cost, no-carbon sunlight, and you’ve got a winner!

Following these simple tips will ensure you get the very most out of your greenhouse grow, and will soon be harvesting a bumper crop of healthy cannabis.

Steven Voser
Steven Voser

Steven is a long-time veteran of cannabis journalism, having delved into every aspect of the subject. His particular interests lie in cannabis culture, the emerging science of cannabis, and how it is shaping the legal landscape across the globe.