For marijuana growers, combining the best of both worlds -- i.e., an indoor growroom and an outdoor garden -- can have major benefits for farmers and their crops. In short, greenhouse growing is one of the best methods for the cultivation of any plant, as it provides for the combination of detailed garden control along with the powerful benefits of our best sources for light: the sun.
So what exactly does the term “greenhouse” mean? Simply put, a greenhouse is a building specially constructed for growing plants under controlled conditions. The building itself is covered with translucent material, so that natural sunlight may enter. In fact, in Europe greenhouses are most commonly referred to as glasshouses, because glass is usually the transparent material of choice. Hence, sunlight, the best part of outdoor cultivation, is brought into an indoor environment.
Aside from sunlight, the grower sets all conditions. While this is an ideal set-up for optimizing a garden’s output, it also requires a great deal of work and management. Let’s start by taking a look at different types of greenhouses before getting into the more technical components of setting up your own personal greenhouse.
Sizes, Shapes & Types
Greenhouses come in a variety of sizes to accommodate any space. There are also a variety of shapes and types to suit each grower’s specific needs and circumstances. The basic three types of greenhouses are; attached, detached and connected.
Attached greenhouses are simple and inexpensive. They are always connected to another building, which cuts down on construction materials and costs because one side of the greenhouse is preexisting. The most common style of attached greenhouse is the lean-to greenhouse, where the greenhouse roof is attached to the preexisting building wall and then slopes away.
A detached, or freestanding greenhouse, is exactly that: a stand-alone greenhouse with four walls and a ceiling. The advantage here is that a detached greenhouse can be constructed to take advantage of nature: sunlight, wind and water. It is not limited in its positioning by a preexisting structure. Detached greenhouses are most commonly referred to as A-frames, or even-span, are the most common greenhouse design. A-frames with asymmetrical rooftops are less common, but more adaptable to hillsides or other rugged terrain.
When multiple greenhouses are joined together they create a multi-span, or connected greenhouse, which are ideal for large format, commercial operations. This connected arrangement makes heating and cooling the gardens inside much more efficient and economical.
Outside of these permanent-structure greenhouses, there are a couple of easy set-up, climate-controlling structures for growing plants on a temporary or smaller scale. Cold frames and hotbeds are two very popular types of greenhouses for the home grower or hobbyist. A cold frame is any structure, usually inexpensive wood or plastic, of any size that is covered with translucent, heat-trapping material such as clear, thick plastic or thin plate glass. A hotbed is simply a cold frame fitted with a heating system. Either can be the size of a large box, or large enough for a human to walk through.
Cold frames are heated by sunlight, which keep operational costs low. However, cold frames are less stable and not durable in extreme weather. They also do not lend themselves to any sort of extensive environmental control equipment as do the larger, more permanent greenhouse listed above.
Greenhouse lighting (outside that of the sun’s natural cycle) usually refers to supplemental, artificial lighting just as one might find in a typical indoor growroom. The uses of supplemental lighting in a greenhouse vary by purpose. The need for additional lighting in a cannabis greenhouse can be attributed to two basic functions. The first is the need to provide longer photoperiods for a seedling or clone nursery (or related mother plants), or to provide longer light cycles for transplanted or vegetating plants not yet ready for flower. The other need is for use in garnering extra annual flower cycles once the sun’s natural photoperiod becomes too short (primarily in winter months or in extreme northern or southern locations).
The first situation usually warrants extended light periods to flower the plants. These areas function just as an indoor nursery or veg room would and may use less intense forms of artificial lighting such as fluorescent light and low-wattage metal halide (MH) bulbs. During the daytime hours when sunlight provides adequate light, the artificial lighting is turned down or off completely. This helps cut down on power usage and costs and makes a greenhouse much more efficient.
Adding a flower cycle (or two) to a greenhouse's annual run follows the same lines as extended lighting for a veg room or nursery, only in this instance the additional light lengthens the grow season to beyond what the sun can provide.veg room or nursery, only in this instance the additional light extends nature’s grow season to that beyond what the sun can provide. In most areas, with the exception of those close to the equator, greenhouse growing is only viable from late spring through mid-fall.
Growers know that an extra cycle or two equals more harvests. Savvy greenhouse growers take advantage of their greenhouse structures to hang HID lamps over gardens. When the sun’s daylight begins to wane below 10 hours, growers can switch to their HID lighting to complete the 12-hour photoperiod for cannabis flowers. This supplemental lighting not only adds an additional crop to their yearly total, but it is more economical than going with a standard indoor grow because the greenhouse will still get a few good hours of sunlight, saving the indoor grower a chunk of money.
Light Deprivation Techniques
With the advent of medical marijuana during the past decade, the use of light deprivation techniques in cannabis greenhouses has become prevalent in the US, though such practices have been in use for centuries. For those new to the concept, light deprivation is a method for reducing the photoperiod or light cycle of flowering plants, whereby the greenhouse structure is covered to block light.
For cannabis cultivation, this process is integral in ensuring that plants stay in flower -- a growth phase that necessitates 12 hours (or less) of light. Once the photoperiod begins to go beyond 12 hours, flowering cannabis plants are in danger of reverting back to a vegetative state. This means that proper light deprivation procedures are critical for cannabis farmers relying on timely crops. Any light leak into a greenhouse garden after the plants have received their full 12 hours can be extremely detrimental to a plant’s development.
By using light dep techniques properly, growers can get an extra harvest during summer months.
To cover a greenhouse and block out sunlight, several different methods may be used. For smaller structures such as lean-tos or cold frames, growers can simply pull tarps over the structure after 12 hours of sunlight. For larger, commercial greenhouses automated shading is usually installed and operated using programmable timers. The latter option, even for smaller greenhouse structures, is preferable because it helps eliminate any human error.
The last thing cannabis farmers need is light hitting plants after the 12-hour photoperiod, and triggering them to revert back to veg. This light-stress confuses plants and inhibits growth and vigor, and may even cause plants to hermaphrodite and produce small seeds. If a grower misses the time to manually cover their greenhouse -- even by a few minutes -- it could have catastrophic effects on their cannabis plants.
Today there are many options for greenhouse farmers who want to utilize light dep techniques for those extra annual harvests. Aside from the automated shades, there are certain types of glass that can self-tint and become opaque to block out light.
Thanks for reading everyone and remember: Grow… And help the world grow, too!
For more on greenhouse growing check out Nico’s Grow Like a Pro DVD, covering indoor, greenhouse and outdoor grow operations. Check out a preview here:
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