How to Build the Best Greenhouse for Growing Marijuana?

You have decided to grow cannabis in a greenhouse, but you don’t want to spend a lot of money. 

Or, you're just tired of growing indoors and want to explore the wonders of growing your plants outdoors, except you want to do it secretly. 

Or maybe you just like some elbow grease and make your own greenhouse. That’s a terrific decision but making one can be tricky, isn’t it?

Well, no longer. Here is a detailed guide on how you can make your own greenhouse the way you like it. You'll see illustrations that help give you an idea, but you can change the plans and create your own if you want. 

Why Should You Construct a Greenhouse?

DIY greenhouses seem like a lot of work. But, if you don't mind the hard work, they offer tons of benefits to cannabis growers, such as:

• You can extend the growing season 
• You gain more control over your cannabis growth
• It saves a lot of electricity as opposed to an indoor growth
• While protecting your plants from external threats like frost, heat waves, pests, strong winds, etc.
• It can make your cannabis buds more potent, aromatic, and flavorful

So, why not simply buy a neat greenhouse and save yourself the trouble, you ask? Well, it's not cheap. It can set you back by hundreds of euros if you want high quality and reliability.

This is where a DIY greenhouse comes into play. A DIY greenhouse can be built in your backyard using some basic tools and DIY skills, and you won’t have to shell out a lot of money from your pocket.

Also, creating a greenhouse is a fun hobby, which lets you immerse more into growing your cannabis plants. Nothing can beat the satisfaction of building your own greenhouse and watching your precious plants bask in it safely!

This is why you should consider a DIY greenhouse. 

What Type of a Greenhouse Should You Build?

A quick Google search will show you tens of types of greenhouses — which can be confusing for new greenhouse growers. Should you just pick the smallest one, or the one that looks the best, or go for the cheapest?

The choice is not so easy. Building a greenhouse involves factoring in different things that entirely depend on your situation and location, like space, DIY skills, budget, materials, preferences, etc. 

To make the narrowing down easier, here are a few popular types of greenhouses you can choose from that fit your needs.

Small Pop-up Greenhouse

A small pop-up greenhouse is exactly what it sounds like — you can pop it up anywhere and fit in a variety of places due to its small size. It is also the most budget-friendly option you can find on the market.

Small greenhouses are best suited for hobby growers growing 2 to 3 plants, which is why they also feature a basic frame and cover, a few shelves to hold the plants, and maybe a zip-up door.

Walk-in Greenhouse

This is a bigger version of the small pop-up greenhouse, and thanks to its larger size, it enables you to walk into the greenhouse and take care of your plants. They still feature the basic frame and covering with a few shelves and a door. 

You can build this in a variety of shapes and sizes, but the complexity of the structure increases with size, so that’s something you must keep in mind. 

Polytunnel Greenhouse

This is a tunnel-shaped greenhouse, which is the preferred choice of commercial growers. It enables you to maximize your space and grow many plants, and due to their structure, they are usually more reliable and sturdy compared to other types of greenhouses. 

Lean-to Greenhouse

Now, if you don’t have space to set up a big greenhouse, or if you want to use your balcony as a greenhouse, this is the go-to choice for you. This type of greenhouse uses a preexisting structure for support and is built around it.

For instance, if you have a balcony, you can use the wall to support the coverings, and depending on your space, it can either be too easy or tricky to set up a lean-to greenhouse. 

The type of greenhouse you choose to build comes down to your space and preferences. You need to ensure that your greenhouse fits in your space while having enough room to move around and the space should be under direct sunlight for best plant growth.

What are the Requirements for a DIY Greenhouse?

Once you have figured out what type of greenhouse you want to build and have selected a location for it, the next step is to build it. But before that, you need to gather all the materials required, such as the following:

• 40 mm PVC pipes with connectors and elbow joints
• Wooden beams
• Wooden boards if you want to grow your plants on raised beds
• Polyethylene sheets or shade netting or something similar
• Duct tape or something similar
• Fans, vents, and oscillating fans depending on your greenhouse design
• Other tools that you require to build the structure and bolt it in place

Remember, you don’t need expensive equipment or materials. You can choose what works best for you, but always choose high-quality materials so that your greenhouse can be sturdy and reliable. 

Also, this is a general guideline but not the only way to DIY a greenhouse.

How to Make a DIY Greenhouse for Cannabis?

Let’s make your DIY greenhouse. Follow these steps.

Find the Best Location for Your Greenhouse

The reason growers prefer a greenhouse is to utilize the natural light for growing cannabis. In addition, a greenhouse provides some sort of discretion without exposing you to others around you. 

However, it's pointless to set up a greenhouse in a location that lacks good sunlight. So, choose a location that gets the most direct sunlight during the day.

For this, find a place and build your greenhouse facing the direction of sunrise — the sun will go over your greenhouse and your plants will get sunlight throughout the day.

Also, ensure that no trees or buildings are blocking the sunlight from reaching your greenhouse. While plants can grow in weak sunlight, consistent sunlight can make a lot of difference. Your goal is to give your plant consistent, direct sunlight as much as possible.

Prepare the Base 

The second thing you must do is prepare the base. Here, you need to decide how you want to grow your plants, whether on raised beds or directly into the soil.

If you choose a raised bed, you have to use wooden boards to make a raised platform for the plants. Here, you can simply install the PVC pipes into the raised bed with metal clamps.

On the other hand, if you choose to grow in soil, you can place wooden beams on the ground and anchor the PVC pipes to them. You can even build a solid foundation if you want to hold the pipes.

The dimensions of the greenhouse depend on the type and size of the greenhouse. So, calculate the size according to the space available and your garden size. 

Prepare the Frame

Now, you have to build the frame of the greenhouse. 

For a basic greenhouse design, you can make a frame using PVC pipes and join them with elbow joints. For a polytunnel greenhouse, you can place two PVC pipes on either side of the base and bend them from the top to meet in the middle. 

The roof of the greenhouse must be at least 2 meters from the base if you are building a small greenhouse.

It is also a good idea to run a beam or wooden beam across the length of the greenhouse, which will act as the spine of your greenhouse, making it sturdier against rough winds. 

There is no right or wrong way to build the frame. You can build it the way you like it, but it is recommended to use as little PVC or wood as possible to ensure the natural sunlight does not get blocked by the frame.

If you want to add a door to the greenhouse, you can make a door frame on any one side of the greenhouse. Again, use wooden beams or PVC pipes to make the structure of the door. 

Add the Walls and Roof 

Your greenhouse is almost ready, since building the frame is the most difficult part. Adding the walls is relatively quite easy.

Based on your climate, you can either use polyethylene sheets or shade mesh. Polyethylene sheets are recommended for colder regions since they let you control the temperature and humidity while protecting against pests and cold wings.

The latter, shade mesh, comes in handy in warmer regions, but note that they do not offer as much control on the greenhouse environment. 

You can also use both in combination, by using polyethylene during the colder months and shade mesh during the warmer months. And you can also use other materials like glass or plastic, but for a starter greenhouse, they can be expensive, harder to maintain, and cumbersome. 

Take the material and align it over the frame, and use a duck tape or something similar to fix them to the frames on all the sides. Do not use nails or zip ties to tie them — cutting a hole in the material kind of defeats the purpose of building a greenhouse and it may rip open in strong winds.

Build the Door and Windows

If you are building a walk-in greenhouse, you need to make a door. Here, for extra security, a wooden door works best. But if you only want a basic door for easy access, plastic sheets work best as doors. 

As for the windows, you can cut windows in the covering material on the front and back of the greenhouse. Ensure the windows are not too big while still allowing easy air exchange to prevent temperature or humidity spikes within the greenhouse. 

Cut windows can be coverable, too, just hand some of the same covering material above the window, which you can pull down when needed. 

Add the Grow Lights

The reason why many people choose greenhouses is so their plants can bask in natural sunlight, but in some regions, that may not be enough. And while you don’t have to invest extensively in massive grow lights, you may still have to invest in supplemental lights. 

Generally, greenhouses require only one-third of the grow lights used by indoor grow setups. 

Using a grow light adds many benefits to your greenhouse, such as the following:

• Grow lights let you control your plant’s growth stages
• They compensate for the lack of sunlight during shorter or cloudy days
• They allow you to set the lighting schedule to 18/6, which is a terrific method for boosting your plant’s growth during the vegetative stage
• Greenhouse covering does not allow 100% sunlight to reach the canopy, and supplemental grow lights can compensate for this

Calculate the Required Light Intensity

To choose supplemental lights for your greenhouse, you first need to know your local natural light DLI (daily light integral) — the quantity of photosynthetic active radiation from the sun in one day. You can know about the local DLI on the internet. 

Next, you need to calculate your glazing material’s visible transmittance. Reputable manufacturers mention this on the specifications, so stick to them. 

To calculate how much light your plant needs, you need to reduce your local natural DLI by your greenhouse’s VT rating. 

The ideal ranges of canopy-DLI for cannabis plants are:

• Seedling or clone stage: 15 to 20 moles/sq. meter/day
• Vegetative stage: 20 to 40 moles/sq. meter/day
• Flowering stage: 25 to 50 moles/sq. meter/day

By subtracting the recommended canopy-DLI from natural DLI, you can find the difference, which is what you have to compensate with supplemental light. Here, you can convert the required DLI into PPFD (photosynthetic photon flux density) using an online PPFD to DLI converter. 

Then, pick the grow light that offers a similar PPFD of light. 

Choose the Right Type of Grow Lights

There are many types of grow lights available in the market — HID, CFL, and LED.

CFL lights are the most affordable types of grow lights, and you can get these in various spectrums. And they are available everywhere! However, CFLs are only suitable for a few plants since they have a low light output.

On the other hand, HID lights are the industry standard as they have a terrific light output that is suitable even for commercial growth. However, HPS lights aren’t the most efficient to run as they consume a lot of energy. Plus, they heat up a lot.

What we recommend for greenhouses are LEDs, since they offer the most benefits. LED lights are easy to set up and use, and although a little expensive, they can help you save up to 70% electricity compared to HID lights and they don’t heat up much. Plus, you can control LED light’s intensity and spectrum easily with the help of a controller. 

LED lights are the future of grow lights, so you can not go wrong with them. And if you are worried about light output, the gap between HIDs and LEDs is quickly narrowing. For a modest greenhouse, high-quality LED lights are more than enough.

Consider Installing Blackout Glazing

Did you know that greenhouses are one of the biggest contributors to light pollution in their local region? And did you know that even a little bit of light during the dark hours can push your plants into re-vegging?

This is why you should consider installing blackout glazing over your greenhouse — to prevent light pollution both inside and outside your greenhouse. Another benefit of adding blackout glazing is that you can force your plant from the vegetative stage to bloom by switching the light cycle to 12/12 from 18/6.

You have three options when it comes to blackout glazing:

• You can simply place a black tarp over the greenhouse covering; this is the easiest and most affordable solution which works surprisingly well
• You can also install blinds on the interiors, but this may be a slightly expensive and cumbersome solution to install 
• Lastly, you can use shutters, which is an easy solution but can cost a lot of money

If you want to be a good neighbor, and protect your plant from light pollution and prying eyes, then adding blackout glazing should be on your checklist while DIY-ing a greenhouse. 

Fix Additional Accessories

Your greenhouse is complete, but there are a couple of other things you may need to add to it, such as the following. 

Temperature and Humidity Control

Greenhouses are prone to getting too warm or humid during the summer months, which can be bad for your cannabis plant. So, it is recommended that you place temperature and humidity monitors in your greenhouse to keep an eye on the temperature and relative humidity.

And depending on your local climate, you may also need to invest in air conditioners and humidity controllers. These devices can help you keep your greenhouse temperature and humidity in check throughout the growing season.

Fans and Ventilation

Depending on your greenhouse size, you may also need to add fans and ventilation. This is because, in larger greenhouses, windows are not enough to ensure a fresh air flow within. So, fans and ventilation can allow the air to flow freely throughout the greenhouse and outside.

When choosing the fans, know their CFM (cubic foot per minute) rating. Their CFM ratings should be equal to or more than your greenhouse’s volume. You can also add oscillating fans in the greenhouse to allow old air to exhale while creating a gentle breeze within.

Automated Watering Systems

While this is not a necessity, automated watering systems can take your greenhouse to the next level. Your best bet is using drip irrigation, which feeds your plant the right amount of nutrient solution throughout the day, preventing the risk of over or under-watering. 

Some Tips for Building the Greenhouse

Here are a few tips that can help you improve your greenhouse:

• Know Your Strains

Each cannabis strain is unique and has unique environmental requirements. For example, some strains can grow in cold climates while others can withstand high humidity. 

Know your strain and know exactly what kind of an environment it prefers. And build your greenhouse based on this.

• Keep Water and Drainage Ready

When designing the greenhouse, keep the watering schedule and drainage in mind. You need to ensure that it is easy to water your plant in the greenhouse, especially if you will be manually watering it.

At the same time, the runoff water should find its way to the drainage easily. Pooling water in a greenhouse is not safe for your plants as it can lead to mold, bacteria, or pest infestations. 

• Plan Everything

When building a greenhouse, plan everything out before you even buy a PVC pipe. Consider everything from your cannabis strain, space available, and local climate to drainage and training. 

Planning everything will prepare you and help you build a greenhouse that works for your plant’s growth, not against it. 

• Use Carbon Filters

If you are building a greenhouse in a residential area, you should consider using carbon filters to scrub the distinct cannabis smell. Some people may find the smell annoying and invite prying eyes.

• Protect Your Greenhouse

A greenhouse can work as a beacon for people to check out your plants, which is something you don’t want when you are growing cannabis. So, use locks and cameras to keep an eye on your greenhouse. And use opaque glazing so that people can’t get a look inside.

Summary: How to Build the Best Greenhouse for Growing Marijuana?

It doesn’t matter if you build a big greenhouse or a lean-to greenhouse on your balcony, as long as you use the high-quality materials and follow the right steps. And as you can see, while building it may seem daunting, the process is quite straightforward.

Start by picking the right location, prepare a base foundation, set up the frame, and adorn it with glazing. Rest, you can add accessories as you see fit, like supplemental grow lights, fans, ventilation, or a door. 

This is a guide to help you get your foot into the greenhouse — pun intended — but this is not all. There is a lot more to growing cannabis in a greenhouse, but this should help you get started.