Supplemental lighting allows the grower to extend the hours of daylight and to improve the quality of light on overcast days. This will give you more control over the vegetative state of your plants.
On a hot day, you experience the science behind a greenhouse when getting into a parked car that has been left in the sun.
Controlling your greenhouse climate is essential to producing a quality product. Some greenhouses have windows or paneling that can be opened or removed to either allow for wind circulation and to cool plants, or to trap in heat.
Solar radiation (energy from the sun) passes through the transparent walls of a greenhouse and heats up soil and plants, keeping a greenhouse warm even when the outside air temperature is cold.
Advanced greenhouses can allow you to grow year-round by controlling light. They can provide supplemental lighting when it’s too dark outside and they can block out all incoming light if it’s too light outside.
Recreating the Cannabis Life Cycle
A common practice among greenhouse farmers is to run cycles of plants known as “light deps”—short for “light deprivation”—during the summer season. By cutting off the amount of light a cannabis plant gets before the end of the season, you can trick it into flowering early. This will allow you to pull a crop early, which is key if you live in a climate that gets cold and wet early in the fall—you’ll want to harvest before the rain sets in and causes your buds to get moldy.
They also allow for year-round cultivation, climate control, and a controlled exposure to sunlight. What’s more, they’re cheaper than growing indoors and produce a more consistent product than fully outdoor grows.
Whether you’re raising cannabis as a cash crop or just for personal use, you have many options for where and how you grow it. It’s possible to grow pot outdoors, indoors or in a greenhouse or high tunnel.
Greenhouse vs. High Tunnel
In many ways, growing marijuana in a greenhouse or high tunnel offers the best option. An outdoor marijuana greenhouse or high tunnel lets you take advantage of some of nature’s benefits, like abundant sun, without having to kneel to nature’s bad side, like frost, storms and deer, rabbits and other pests.
Growing Marijuana in a High Tunnel or Greenhouse
Many folks in northern latitudes start their seeds indoors in April under grow lights and transfer them to a greenhouse in May. Your own schedule will depend on your climate and growing season, of course.
Even in warm climates, many greenhouse growers supplement the natural light with additional light on cloudy days. These days LED grow lights can be used to provide additional illumination which can be automatically switched on when ambient daylight (PPFD) levels drop too low. Growers in cool climates, such as Scandinavia may prefer to use supplemental HPS lighting which offers both light and heat to the plants. Supplemental lights also allow you to extend the natural sunlight hours. This would allow you to grow autoflower seeds in a greenhouse and have 18-20 hours of daily light. Artificial light would be used to give the autoflower plants their preferred 20 hours of daily light with optimized yields and quality.
Sophisticated greenhouse growers have watering systems in place to simplify and even automate water delivery. If the greenhouse is not in an entirely private location then it might benefit from a coat of white shading paint. This is sold in garden centres and used to protect greenhouses from overheating on the hottest summer days. For the cannabis grower this shading paint also stops people seeing what is inside your greenhouse, but green plastic plant mesh and tomato plants have also provided excellent cover for many generations of greenhouse growers.
Greenhouse growers are split into two main groups; those that grow their cannabis plants in plant pots and those that grow them directly in the ground. Plant pots can be easily moved if they need to be, for example if visitors, extreme weather or other problems are present. But plant pots will need more frequent watering and occasional feeds. A large cannabis plant in a 10 litre container will need watering daily during very hot weather. That could be a problem if you are away and unable to visit your plants.
Greenhouse growing of cannabis has lower ongoing costs compared to indoor growing, where large amounts of cash are spent on grow lights and ongoing electricity use. By contrast, growing cannabis in a greenhouse only requires a seed and some substrate to grow in. The sun provides free energy for your plants to grow.
Where to locate your greenhouse?
Some people copy the large legal greenhouse growers in the USA and fit an extraction fan to pump humid stale air out of the greenhouse. This can be combined with a carbon filter to remove any cannabis aroma from the exhausted air.
If you get a greenhouse it pays to think carefully about the location. When it comes to security, always think about a location which makes it difficult for neighbours or the public to see/smell your crop. Also consider your local climate. If you are living in a cool climate it pays to locate the greenhouse where it will receive maximum sunlight for as much of the day as possible. If you live in a hot, desert climate you may want to consider locating the greenhouse under some trees which will shade the greenhouse during the hottest hours of the day in mid-summer. Mediterranean greenhouse growers may wish to place their greenhouse in a cooler, northern part of the garden where some shade may be present. Remember that when temperatures reach 40-45ºC the temperatures become damaging.
Greenhouses offer protection from the elements, insect predators and grazing animals. Greenhouses also provide a longer growing season. You can plant your cannabis seeds a little earlier than if you were growing outdoors. The greenhouse also protects your plants form the worst of the autumn weather during harvest, allowing you a greater chance of a safe harvest.
How do I get rid of excessive greenhouse humidity?
As a result, a greenhouse allows you to grow larger plants which can start earlier and finish later than would be possible growing outdoors without a greenhouse. Many growers of photoperiod feminized seeds routinely harvest several hundred grams, or more, of dried buds from a single plant. Plants can easily reach 2-3 metres tall and just as wide. A greenhouse also protects your plants from the autumn/winter storms. This can allow the greenhouse grower to grow a broader range of later blooming cannabis seeds than is possible outdoors.
The more professional greenhouse grower will take care to introduce new, good quality soil/fertilizer each year and keep the greenhouse clean and tidy to minimise potential for pests and disease. Some greenhouse growers use strategically placed fencing and shrubs to make the greenhouse inaccessible to unwanted visitors and invisible to prying eyes. Greenhouses are cheap to buy. You can buy small low cost plastic ones for not much more than a hundred euros. Even cheaper ones are available with plastic covers. They are available everywhere and come in any shape/size required for all budgets. Some of the modern polycarbonate greenhouses are also opaque giving instant privacy and have lockable doors. What more could you need in your back garden? Remember that poor quality cannabis seeds can’t produce connoisseur quality cannabis, no matter how well you grow them. Invest in the best cannabis seeds you can get from a company with a proven reputation, and enjoying growing your own cannabis in a greenhouse.