Chapter 6: Grow Rooms & Greenhouses

Marijuana Horticulture: The Indoor / Outdoor Medical Grower’s Bible

by Jorge Cervantes

The best location for a grow room is in an obscure corner of a basement, where the temperature is easy to keep constant year-round. Basements are well insulated by concrete walls and soil. A basement room can be enclosed and camouflaged with junk, a double wall, workbench, or shelving.

Added security is afforded by installing a false door in a closet. The grow room is located behind the secret door. Another good secret location, except the possible heat buildup, is the attic. Few people venture to an attic that is difficult to access. Some growers locate their gardens below a trapdoor covered with a rug.

Law enforcement cannot use the electricity bill as sole grounds for a search warrant. But they can use it along with other “evidence” such as remnants of indoor growing visible outdoors, thermal image heat signatures, snitch testimony, etc., to secure a search warrant. As long as marijuana grown is not sold or shown to a snitch, there should be no reason for any suspicion. Thermal image technology is easy to outwit. Just keep the lights n during daylight hours to confuse the technology. Or, cool exhaust air and expel it under the well-insulated grow house so it does not leave a heat trail.

Outbuildings, garages, and barns not attached to homes are some of the worst places to grow cannabis. Thieves and law enforcement often do not regard entering a barn or garage as a crime, though they would not consider entering a home. Security is much better when the garden is within the home.

Although less common, there are even grow rooms on wheels! Some innovative growers have remodeled trailer houses and buses int grow rooms. One of my favorite grow rooms was a tricked out trailer. Another was a 60-foot sailing yacht!

The grow room’s size determines the size and the number of lamps. High intensity discharge (HID) lamps that work well to grow marijuana are available in wattages of 150, 175, 250, 400, 600, 1000, and 1100. Smaller wattages from 150-400, work well in closets or spaces with 9-21 square feet of floor space. use 600-watt and larger bulbs for larger areas.

The most productive setups utilize two rooms. The first room is for vegetative growth, mother plants, and rooting clones. This room should be about one-quarter the size of the flowering room. When the flowering room crop is harvested, plants from vegetative room are moved into the flowering room.

Super productivity is achieved with a perpetual crop. Several clones are taken every day or every week. Every day a few plants are harvested. For every plant harvested, a new cutting takes its place.

Setting Up the Grow Room – Step by Step

Set up the grow room before introducing plants. Construction requires space and planning. A grow room under construction offers a terrible environment for plants. Once the grow room is setup and totally operational, it will be ready for plants.

Step One – Choose an out of the way space with little or no traffic. A corner of the basement or a spare bedroom are perfect. A 1000-watt HID, properly setup, will efficiently illuminated up to a 6×6 foot room. The ceiling should be at least five feet high. Keep in mind that plants in containers are setup at least one foot off the ground, and a lamp needs about a foot of space to hang from the ceiling. This leaves only three feet of space for plants to grow. If forced to grow in an attic or basement with a low fur-foot ceiling, much can be done to compensate for the loss of height, including cloning, bending, pruning, and using smaller wattage lamps.

Step Two – Enclose the room, if not already enclosed. Remove everything that does not pertain to the garden. Furniture, drapes, and curtains may harbor fungi. An enclosed room allows easy, precise control of everything and everyone that enters or exits, as well as who and what goes on inside. For most growers enclosing a grow room is simply a matter of tacking up some plywood or fabricating plastic walls in the basement or attic and planting the room flat white. Make sure no light is visible from the outside. If covering a window, do so discreetly – it should not look boarded up. Insulate windows and walls so a telltale heat signature does not escape. Basement windows often are painted to look like the foundation. Place some stuff – books, personal effects, household goods, etc. – in front of the window, and build a bx around the things so a natural scene is visible from the outside. At night, bright light leaking through a crack in an uncovered window is like a beacon to curious neighbors and bandits.

Step Three – Cover walls, ceiling, floor – everything – with a highly reflective material like flat white paint or Mylar. The more reflection, the more light energy available to plants. Good reflective light will allow effective coverage of an HID lamp to increase from 10 t 20 percent, just by putting a few dollars worth of paint on the walls. Reflective white Visqueen plastic is inexpensive and protects walls and floors.

Step Four – Constant air circulation and a supply of fresh air are essential but often inadequate. They should be at least one fresh air vent in every grow room. Vents can be an pen door, window, or duct vented outside. An exhaust ran vented outdoors or puling new air through an open door usually creates an adequate flow of air. An oscillating fan works well t circulate the air. When installing such a fan, make sure it is not set in a fixed position and blowing too hard on the tender plants. It could cause windburn and dry out plants, especially seedlings and clones. If the room contains a heat vent, it may be opened to supply extra heat or air circulation.

Step Five – The larger your garden becomes, the more water it will need. A 10 x 10 foot garden could use more than 50 gallons per week. Carrying water is hard, regular work. One gallon of water weighs eight pounds; 50 x 8 = 400 pounds of water a week! It is much easier to run in a hose with an on / off valve or install a hose bib in the room than to schlep water. A three foot watering wand attached to the hose on / off valve makes watering easier and saves branches from being broken when watering in dense foliage. Hook up the hose to a hot and cold water source s the temperature is easy to regulate.

Step Six – Ideally, the floor should be concrete or a smooth surface that can be swept and washed down. A floor drain is very handy. In grow rooms with carpet or wood floors, a large, white painter’s drop cloth r thick, white Visqueen plastic, will protect floors from moisture. Trays placed beneath each contained add protection and convenience.

Step Seven – Mount a hook strong enough to support 30 pounds for each lamp. Attach an adjustable chain or cord and pulley between the ceiling hook and the lamp fixture. The adjustable connection makes it easy to keep the lamp at the proper distance from plants and up out of the way during maintenance.

Step Eight – There are some tools an indoor gardener must have and a few extra tools that make indoor horticulture much more precise and cost effective. The extra tools help make the garden so efficient that they pay for themselves in a few weeks. Procure all the tools before bringing plants into the grow room. If the tools are there when needed, chances are they will be put to use. A hygrometer is a good example. If plants show signs of slow, sickly growth due to high humidity, most growers will not identify the exact cause right away. They will wait and guess, wait and guess, and maybe figure it out before fungus attacks and the plant dies. When a hygrometer is installed before plants are brought int the grow room, the horticulturist will know from the start when the humidity is too high and causing sickly growth.

Step Nine – Read and complete: “Setting Up the HID amp” at the end of Chapter 9.

Step Ten – Move seedlings and rooted clones into the room. Huddle them closely together under the lamp. Make sure the HID is not so close to small plants that it burns their leaves. Position 400-watt lamps 18 inches above seedlings and clones Place a 600-watt lamp 24 inches away and 1000-watt lamp 30 inches away. Check the distance daily. hang a precut string from the hood to measure distance.

Greenhouses and Cold Frames

This simple overview of greenhouses and cold frames will give you a feeling of what to look for and how to plan your project and reap a heavy harvest.

Greenhouses, cold frames, and hot frames are all useful in extending the growing season and / or protecting new plants and seedlings. Which type of structure you select depends on the size and location of your growing area, how much money you have to spend, how much time you have to grow, and security issues, Simple cold frames and hot frames can be assembled from common materials like old framed window panes and hay bales. Greenhouses are generally larger and more com0plex. They can be expensive t build and maintain but offer more flexibility for growing time and building use.

When deciding on a growing structure, first carefully analyze the project on paper. Consider how much space you have for the footprint and how many plants you can grow safely. Cold frames are small and can be as simple as glass or plastic frame set on the ground with no artificial heat source. Their basic function is to protect young plants and seedlings from wind and cold in the early spring, but they can also be blacked out to induce early flowering and harvest. Hot frames are similar in size and structure but provide heat through manure, electricity, steam, or a hot water pipe). You may use a hot frame to raise early seedlings and clones, after which the structure can be converted into a cold frame. Both frames share the advantages of economy, simplicity, small size, and portability.

Both large and small greenhouses cost more money, time, and space. With the exception of the lightweight “hoop” house or miniature greenhouse, they are also more permanent. The type of greenhouse selected will be determined by the planned use of the space and where it will be located. A lean-to or attached greenhouse will probably be smaller and less expensive to build than a freestanding structure.

Total area of the greenhouse is determined by the number f plants you intend to grow. Allow one square yard per mature plant. Do not forget to allow about six inches space fr air circulation between benches and side walls. Add space for walkways – standing room only or room for a wheelbarrow – and possibly a center bench. Glass, plastic panels, and sheeting all come in standard widths, and it is easier t build in size compatible with these units rather than have to cut panels down.

Budget, building skills, and security will weigh heavily in the decision making process. The least expensive structure per square foot is an even span 16-foot wide that will house two side beds or benches, two walks, and a wide center bed or bench. An 8 to 123 foot wide lean-t with wide beds or benches and a central walk is the least expensive option overall. Whichever option you choose, building it yourself can be cheaper and more secure than hiring a contractor. You can purchase much f the plumbing and electricity installations in kits or pre-assembled to avoid compromising security.

Climate will play a role in choosing your greenhouse. For example, a cold frame in the mild Pacific Northwest can give you a six week jump on the growing season. This would not work in a colder region like the upper Midwest. Likewise, a hot or tropical area will require more shade and water. While the large cold frame is the most economical of structures, it will not function a s a cold-climate garden. Location and exposure will depend on climate, but in general, you will want the greenhouse to be sheltered from curious eyes and strong winds and to be away from any areas where failing limbs or other debris might be a problem.

There are a number of external design options. Cold frames can be as simple as a window sash laid over a rectangle of straw bales or a piece of plastic stretched over a metal or PVC pipe frame and held in place with camps. Duct tape also works wonders to keep plastic in place. The advantage to plastic sheeting is that it can be removed during the day t take advantage of fresh air and the sun’s warmth and then replaced at night to protect plants from cold air. The cold frame can be easily converted to a hot frame by installing electric heat and a watering/misting system.

Greenhouses can be attached (lean-to, window-mount, even-span) or free standing. A lean-to uses an existing structure for one or more sides and is limited to a single or double row plant benches with a total width of seven to twelve feet and length up to that of the building. Without considering security, the advantages of a lean-to are its proximity to electricity, water, and heat, but on the downside are its limited size, light, ventilation, and temperature control.

A window-mount replaces an existing window providing a relatively low cost way to grow short plants, small seedlings, or clones. It can be installed fairly simply with common household tools. The disadvantages are its small size and possibly public view.

Low profile greenhouses are perfect from crops of short plants. It is easy to setup a low profile hoop house or a greenhouse alongside a building that gets full sun. The short greenhouse or cold frame is simple to darken during full summer and lets you reap the benefits f the harvest early!

Small greenhouses and cold frames also work well on patios, balconies, and rooftops. They protect plants from wind and prying eyes of neighbors.

An even span can be an attractive option. Like the window mount or lean-to, the even-span is attached to the house and bears similar limitations of size, light, ventilation, and temperature. Unlike the lean-to or window mount, the even-span can be larger and can open into the house – providing heat and humidity – or even function as a conservatory, an attractive place to relax. It is, however, more expensive to heat and maintain. Such greenhouses are most popular where security is a minimum concern.

The freestanding greenhouse offers the most flexibility in size and location. It can be built to take full advantage of the sun, but it does not retain heat well and can be expensive to keep warm. Many frame types and coverings are available in kits or raw materials.

Framing can be in wood or metal. You may select a panel frame which is more expensive to build but has the advantage of quick installation and breakdown for storage. If portability is an issue, there are miniature greenhouses and hoop houses which can be purchased as a kit for under $300. These structures, because they can be picked up and moved, are usually considered temporary by municipalities, and often do not require permits.

Plastic is much cheaper than glass, can be heated as effectively as glass, and is equal to glass in producing quality plants and buds. Polyethylene (PE) is low cost, lightweight, provides ample light, and can withstand fall, winter, and spring weather. It does not tolerate summer UV levels, however, and must be replaced annually. Ultra-violet inhibited PE lasts longer, but both types lose heat more quickly than glass. During the day, this can help keep plants cooler, but at night the heat loss requires the use of artificial heat source. Poly Weave is a plastic fabric made of 8-mil polyethylene reinforced with nylon mesh. it transmits up to 90% sunlight, can be sewn or taped, and has a lifespan of up to five years.

Polyvinyl chloride (PVC) is two to five times more expensive than PE but can last five years or longer. PVC is pliable, transparent, or translucent, and comes in four to six foot widths which can be sealed together to provide a super wide piece. Ultraviolet inhibited corrugated plastic panels provide another option. The panels can be used in cold frames, propagation houses, and greenhouses to provide excellent wind and snow protection and optimal solar heat collection.

Corrugated fiberglass is lightweight, strong, and comes in eight to twelve foot panels. Poor grades will discolor, reducing light penetration, but a good grade of clear fiberglass can cost as much or more as glass. Its lower weight has an advantage, and it is more difficult to see through!

Framework and covering are only the beginning. Growing plants in a greenhouse is often more demanding than growing plants indoors. Air temperature, humidity, light, and air quality must all be controlled in relation to a constantly changing greenhouse climate.

Climate Control

Even the best greenhouses will lose heat through radiation, conducting, convection through glass, walls, and floor (or soil), and also through vents, doors, and cracks. To counteract external variables, the internal structure of the greenhouse is, in some ways, more complex than the selection of framing and covering materials.

All greenhouses need ventilation and most need fans. Look for an extraction fan with the capacity to change the air once every minute. Capacity refers to the amount of power needed to circulate the air volume of your structure.

Calculate the volume by multiplying the square footage of your greenhouse by the height. Multiply the volume by sixty air changes per hour to get the cubic feet per minute capacity of the greenhouse.

The combination of louvers and fan will force the hottest, most humid air out while protecting the plants from draft. Vents control temperatures in all seasons and improve growing conditions. Hand-operated roof vents will require frequent checks, or you may install automatic vents with with an electric motor and thermostat that will respond to conditions around the clock. Venting is important with a cold frame, too. The high end models have wax-filled vents that operate automatically, opening when the heat rises in the frame and contracting as the temperature cools.

Heating systems are important to keep plants healthy during cold nights. Cannabis grows well with night temperatures of 60-65F, but colder nights will require an additional heat source for sustained growth.

You can turn a cold frame into a hot frame by insulating it with manure or heating it with steam, hot water pipes, or electricity. To make the most efficient use of electricity, purchase soil-heating tape or cable, with a thermostat that will automatically control the temperature. Lay the cable on the soil at the bottom of the bed or on a bed of sand or vermiculite and cover with about two inches of sand. You will need to provide 10-15 watts of electric heat for every square foot of growing area. Heat cables are also useful in greenhouses for warming seedlings, clones, or flowering plants without the cost of heating the entire structure.

Small greenhouses can be heated relatively economically with an electric space heater, or more effectively with thermostatically controlled forced air using ducts or plastic tubing to distribute heat. Larger units may be heated with forced air or by a coal or natural hot-water or steam system. Steam can also be used t sterilize growing beds and potting soils. Then there is the low tech method of greenhouse warming: compost. A grower in Portland, Oregon, stacks organic matter on the sides of the greenhouse to a height of about five feet inside and out. As compost decomposes, it gives off heat keeping the structure warm at a very low cost.

Evaporative cooling eliminates excess heat and add humidity, reducing water needs. Moist air circulates through the structure while warm air is expelled through roof vents or exhaust fans. Properly installed, a cooler can reduce the interior temperature by as much as 30-40F in hot, dry climates, less in wetter areas. As with fans, the size f the cooler is determined by the size the greenhouse. A general guideline is to find a cooler equal to the cubic space of the structure plus 50%. To provide both cooling and humidifying effects, the cooler must be installed on the outside of the greenhouse; otherwise, it simply humidifies without dropping the temperature.

Misting and watering are also important components of greenhouse gardening. Extended periods of growing and higher sustained temperatures make adequate water essential. Again, there are methods to suit every temperament from low tech to automatic.

Most companies offer watering and misting systems by component, which can be mixed and matched to suit grower’s needs. Automatic systems will have a timer that triggers the mist or water at preset intervals. You may want a toggle switch that allows you to rotate between manual and automatic watering.

A lower tech method of mist and watering control consists of a series f screens that tilt downward with the weight of the water shutting off the flow then raising to restart the cycle as the screens dry. It is fully automated by the weight of water or lack thereof. Of course, there is also hand-watering which is very effective and requires no mechanical intervention. Automatic systems, both high and low tech, are alternatives to hand watering which can be most helpful during a gardener’s absence.

heating and watering devices depend on that other cost of greenhouse keeping: how much time the grower has t spend tending plants. You can keep equipment costs to a minimum if you plan to spend a lot of time in the greenhouse. For growers who are away from the structure for long periods, automatic systems are a good investment.

In addition to shelter, heat, water, and ventilation, plants need light. This section will offer a brief treatment of lighting. Fluorescent light offers higher efficiency with low heat and is the most widely used. Incandescent light – 60-500 watts – may be used t extend day length. High intensity discharge (HID) offers long life, and the sodium lamps emit the best light to be combined with natural sunlight. Regardless of light source selected, you may want t purchase a light meter. It will be very useful in setting the light lever in your greenhouse for maximum efficiency.

Carbon Dioxide (CO2) is another important aspect of the greenhouse environment that will be only touched upon in this section. Closed greenhouses often have too little CO2 during the day for plants to be able to use light effectively. Enhancing the levels of CO2 will accelerate plant growth; methods for doing s range from expensive CO2 equipment with infrared sensors to block dry ice kept in a pressure bottle until needed.

Security is always a concern when growing cannabis. There are several ways t camouflage the greenhouse such as growing other plants with the cannabis. Paint the walls with sun blocking paint so light still enters but prying eyes do not. Go to the discount store and purchase artificial flowers. Put the artificial flowers on and around the cannabis plants so it looks like they are growing from the cannabis. Remember to pay attention to other plants that could be blooming during this time and follow suit.

Planting in the earth floor of the greenhouse allows you to use organic methods. The plants cannot be moved easily, but they grow bigger and require less maintenance than container-grown plants. Without containers, plants also retain a lower profile. Growing in Mother Earth is always better than planting in pots!. Most all the principles that apply to outdoor growing apply to growing in a greenhouse, too.

Greenhouses can be darkened to induce flowering during mid summer. This practice will allow you to harvest up to three crops a year! Cannabis plants flower when nights are long (12 hours) and days are short (12 hours). Darken the greenhouse so that plants receive 12 hours of uninterrupted darkness every day to induce flowering. When the greenhouse is darkened daily so that plants receive 12 hours of darkness, a crop of clones planted May 1st can be harvested by the middle of July.

Automatic darkening machinery is available for large commercial greenhouses. Smaller greenhouses are normally covered with black plastic to “black out” the interior for 12 hours.

When combined with natural sunlight, artificial light is optimally used during non-daylight hours. Greenhouse growers turn the HID lights on when sunlight diminishes (30 minutes before sunset) and off when sunlight strengthens (30 minutes after sunrise). Turn on the HID when the daylight intensity is less than two times the intensity of the HID. Measure this point with a light meter. Turn off the HID when the daylight intensity is less than two times the intensity of the HID. A simple photocell that measures light intensity can be used to turn the lights on and off automatically.

Supplementary lighting has greatest effect when applied to the youngest plants. It is least expensive to light plants when they are small.

Many different types of covering are available for greenhouses and cold frames. The best greenhouse films are UV (ultraviolet) resistant and still transmit plenty of light. Lexan is rigid and full of thermo-storing channels. It is one of the best greenhouse plastics available. Lexan lasts for years and transmits almost as much light as glass while retaining greenhouse heat. The only problem with Lexan is that it is clear. Some growers disguise greenhouse cannabis by wiring ornamental plastic flowers to the branches visible to passers by, which is advisable where neighbors are not curious and laws lax.

Regulating heat in a greenhouse is much more difficult than in an enclosed grow room. Greenhouses heat up quickly on sunny days, and cool equally fast when the sun ducks behind a cloud or drops below the horizon. This fluctuation in heat is difficult and expensive to control. Hot and cold dips also affect the ratio of nutrient to water plants plants need to use, which makes growing in a greenhouse more demanding than growing indoors.

Marijuana Horticulture

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