Why You Should Grow Cannabis In A Greenhouse Or Conservatory

Max Sargent

Cannabis Journalist & Psychedelics Expert

Max Sargent

Last updated: April 17th, 2024

Popular culture is full of images of foil-lined rooms with hot lights and rows upon rows of flowering cannabis plants. However, the best weed is usually grown under the sun, using natural light. In some parts of the world, the great outdoors is best; in others, the assistance of a greenhouse can really optimise the process.

In this article, we look at growing cannabis in greenhouses and conservatories, exploring the benefits and drawbacks, then providing some tips on how best to do it!

The differences between greenhouse and conservatory growing

While there are no stark differences between the two, there are some small disparities. In a nutshell, a greenhouse is made strictly for plant cultivation and is usually separate from one’s living quarters. A conservatory, meanwhile, is often an extension of one’s house, and may perform other functions than just gardening. Both spaces are often made from glass. You might also hear a conservatory referred to as a “sunroom”.

However, conservatories can be small and hot, or they can be large and airy. While both harness the power of sunlight, not all conservatories are particularly well-suited to growing cannabis (or other plants). Greenhouses, on the other hand, are—so long as they’re placed appropriately.

Different types of greenhouses

There are four main types of greenhouses, and these can come in a range of shapes and designs:

• Pop-up greenhouses: These structures are small, and thus are the perfect choice for novice hobbyists and those with very little space. They are very cheap, starting at around £30, and are made with a plastic or metal frame, and come with a plastic cover. One side will have a zip, allowing access. Inside there will be shelving, which you can usually adjust to your needs. Pop-up greenhouses can be used indoors or outdoors, and are great for growing one or two cannabis plants.
• Walk-in greenhouses: These are like larger pop-up greenhouses. Similarly designed, they are significantly bigger, allowing you to fully access the space. As well as giving you greater ease of access to your plants and equipment, they make it easier to grow more plants and to fit in more lights, exhaust systems, and so on. Usually, these greenhouses are positioned outdoors or in very large indoor spaces.
• Polytunnels: Now we’re getting serious. These tunnel-shaped greenhouses take up a lot of space and can fit a huge amount of plants in them. If you fill a polytunnel with weed, you’ll have a very big harvest. Otherwise, you could grow cannabis alongside a range of other plants. Polytunnels can only realistically be used outdoors, but give you very good access to your plants.
• Professional greenhouses: These can vary in size, but are built of sturdy, high-quality materials, and as such can be expensive. Still, if you want to grow a lot of weed in a greenhouse, then the investment can be worth it, especially if you’ll be rigging up equipment too.

What size greenhouse is best for cannabis?

The ideal greenhouse dimensions for your grow will chiefly come down to your spatial restrictions and how much weed you want to grow. It might be great to have a polytunnel, but if it doesn’t fit in your garden, there’s not much you can do about it. Moreover, if you want to grow one big, healthy plant, then a little pop-up greenhouse will suffice. If you want to grow 100 plants, then you’ll need a polytunnel or professional greenhouse.

For the vast majority of casual growers, a pop-up or smaller walk-in greenhouse should be big enough for your needs.

The pros and cons of growing weed in a greenhouse or conservatory

Like every other cannabis cultivation method, there are some advantages and disadvantages to making use of a greenhouse or conservatory for your grow.

Pros of greenhouse growing

In terms of advantages, greenhouses and conservatories are often more cost-efficient than indoor operations. You also benefit from the natural heating functions of the greenhouse, which is especially useful when outside temperatures are low, or if you want to grow cannabis plants that thrive in hot and humid conditions, such as Thai sativas.

Furthermore, you have the option of providing supplemental heating and/or cooling systems if necessary, which gives you a lot of flexibility. In the summer, you can use a greenhouse to grow naturally, and in the later months, you can use sunlight where possible, and then supplement it when necessary.

The transparent covering allows you to harness the power of the sun to help your plants grow healthily and vigorously, without spiking your electricity bill. And compared to garden growing, a greenhouse or conservatory is better at keeping your herb out of sight from nosey neighbours and certain critters too.

The pros of greenhouse and conservatory growing are:

• Harnesses the power of sunlight
• Creates optimal environment for growing weed
• Cheaper than indoor growing
• More control compared to outdoor growing
• Extends the growing season
• Keeps other people and certain pests away from your crop

Cons of greenhouse growing

A downside to these methods, however, is that your plants’ growth is largely contingent on the natural light cycle. Unlike a true indoor grow where the grower must manually change the light cycle to initiate the flowering phase, greenhouse and conservatory plants will naturally make the switch from veg to bloom when Mother Nature says so.

With that said, growers can construct supplemental light systems if need be. The same can be said for light deprivation systems. If possible, strategically plan out the start of your grow in advance to give your plants ample time to grow and mature under the summer sun before the cold, dark months arrive.

Another potential drawback is that, compared to indoor growing, you lack some control regarding certain pests and diseases when growing in a greenhouse, so it’s best to keep a careful eye out.

Finally, with conservatory growing specifically, your ability to harness the sun really depends on which direction your conservatory faces. If it faces south, it’s going to be perfect for growing weed. If it faces west or east, it will be imperfect but should work in places that get a lot of sunny days. If it faces north, you probably won’t get enough direct sunlight to give your plants the energy they need to grow properly.

The cons of greenhouse and conservatory growing are:

• Without supplementation, you are limited to the normal growing season
• Offers less control compared to indoor growing
• Higher chance of pests and disease (compared to indoor growing)
• For best results, conservatories should be south-facing

Tips for growing cannabis in a greenhouse or conservatory

Now that you know the pros and cons of growing in a conservatory or greenhouse, here are some tips and tricks to take advantage of.

Choose good genetics

Remember that, first and foremost, you need to buy cannabis seeds with high-quality genetics if you’re looking to optimise any grow for success. Even if you take excellent care in maintaining the best greenhouse environment possible, bad seeds are still bad seeds.

Start early

To maximise the rewards of your greenhouse grow, start by determining the best time to begin cultivating. Ideally, you’ll want to start early in the year, allowing your plants enough time to sprout and go through the vegetative phase with ease. This is the time when plants grow strong branches and produce fan leaves, before forming flowers. A robust veg stage is the foundation on which quality buds are built.

Most greenhouse growers will germinate their seeds indoors under CFL lights. This means that you can start seeds around two weeks earlier than you would outdoors, giving them two weeks of extra growth, and keeping them protected during the most vulnerable stage of their lives.

Automated systems

A greenhouse can make the workload for the grower a lot easier since it provides a perfect sanctuary for plants to receive automated watering/feeding. This system is great for busy folks with not a lot of free time to constantly observe their babies. However, it is still important to pay close attention to your automated system, should anything go awry.

Automated systems can range from a timer on a light, to a drip irrigation system, to a complex network of pumps and fans hooked up to hygrometers, thermometers, and so on.

Hygrometer / Thermometer

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Security

Marijuana cultivation can still be a risky business, even in this day and age of recreational legalization in many parts of the world. With that being said, discretion is key. Growing in a greenhouse is a good option, but you have to make sure that it is done stealthily.

One way to do so is by painting the exterior with some white shading paint, just to mask what is going on inside. You can also add companion plants like tomatoes and mint, or even a green plastic plant mesh, to camouflage the sight and smell of your precious herb. Also, greenhouses will keep your plants secure from most larger pests, as long as it’s securely enclosed. Small and microscopic invaders, however, still pose a threat.

Common greenhouse and conservatory growing mistakes

When growing in a greenhouse, in addition to knowing what to do, it’s important to know what not to do. Though it’s pretty straightforward and very similar to growing in other spaces, here are some common issues to look out for:

• Overwatering: This is common to all cannabis grows, but as a greenhouse is a closed-off, humid environment, the soil can dry out more slowly compared to in other environments. So, always ensure the soil is actually dry before you water it.
• Poor climate control: Greenhouses, though on the whole a very good environment, can get too hot or too humid, especially in the height of summer. As such, you should open them up at least once a day to let out excess heat and humidity. If not, you might be met with stunted growth and the presence of nefarious fungi!
• Bringing plants out too early: Just because greenhouses make for a warmer environment doesn’t mean you can bring plants out too early. For one, it may still be too cold for them. But more importantly, before a certain point in the year (around March 21st in the Northern Hemisphere) there just won’t be enough natural light to properly sustain your plants.

Master the art of greenhouse and conservatory growing

Using a greenhouse is undoubtedly one of the best ways to grow cannabis. Though not as optimised, the same general principles apply to growing in a conservatory, so long as it gets enough direct light.

The drawbacks to these methods are greatly outweighed by the benefits, and if you can grow cannabis in a greenhouse, there’s really no reason not to. At the very least, it makes summer growing even more productive, and with a little supplementation, you can greatly expand the growing season.