Chapter 4 – Growing Top Shelf Buds
This is chapter 4 of a 14 part weekly series with highly specific how-to guide for hydroponic system set up. Follow step by step to grow top shelf harvests like a pro. The information and instructions are highly scalable. These proven and well developed methods and technologies will work for anyone. Whether you want to grow some personal crops of buds at home or if you intend to fill a warehouse.
In our hydroponics cultivation model we are going to set up horticultural trays or commonly referred to as “Food Tables” or “Drip Tables”. These are simple large sized and relatively shallow plastic trays, typically ABS. They are sturdy enough to support plants and large volumes of water without leaking or buckling. A good tray design has plenty of drainage channels built into the bottom. These channels help nutrient solution drain away quickly and freely from pots or grow cubes. They give space for air between the roots at the bottom of containers or cubes and the bottom inner surface of the tray. While relatively light in weight, they can be cumbersome to move around or transport.
Horticultural trays are widely available and in an array of sizes. Most common sizes available are 2’ x 4’, 4’ x 4’, 4’ x 8’ and 3’ x 6’. Note that these are rarely the exact dimensions. Typically this is the inside measurement of the tray so in reality they are slightly bigger in outside dimensions. Typical depth of trays is from four to six inches. Horticultural trays are available often in black although white trays are also available. Black tends to have less problems with algae growth. Some growers prefer the light reflectivity and lower surface temperatures of white trays under bright grow lights.
The 3’ x 6’ trays while a little harder to find, are good to work with and recommended. These give the grower two square meters with a little outside edge space. This size also happens to fit snugly into pallet racking which leads us into discussing support trays and the overall layout.
In an eight foot by twelve foot grow room it is possible to fit three 3’ x 6’ horticultural trays on stationary racks. This will provide enough space between trays for the average person to carefully maneuver around to work within the room.
Horticultural trays need to be supported well. Metal is preferred material because it is nonporous and will not harbor mildews or bacterial growth from moist environments like wood can. Metal shelving, pallet racks, etc. are available widely. Further, they often allow for adjustable heights and allow for multiple levels to be supported safely in the same rack. Usually, you need at least twelve to eighteen inches of clearance between the bottom of your tray and the ground surface below. This distance allows for reservoirs or catchment bins to be placed underneath the trays, out of the way and out of strong light.
Some hydroponic growers use wooden sawhorses, about every two feet underneath the horticultural trays for support. Other growers have constructed benches with heavy duty castors to create a moveable tray. This allows for a floating aisleway so you can make the most use of space available to you,
Professional grade Rolling Benches are also available, although they are typically geared towards four foot wide horticultural trays. Rolling bench systems make use of a stationary lower support that is narrower than the actual tray. The tray sits on top of steel rollers and can be moved about a foot or so from side to side. This becomes a great benefit when there are multiple trays in the same area. This way only one aisle way is needed for many trays. The aisleway can be opened between the benches by simply rolling the trays sideways for up to 80% linear space use efficiency. Consider stacking trays vertically, you can achieve 200%+ space use efficiency, even if there are some permanent aisleways between racking.
If you want to stack your trays vertically, there are some considerations, namely vertical space use. With fast low growing cannabis strains under high powered LED grow lights, you will need at least four feet of vertical space per “deck” or tray. More is better. Running out of vertical room means plant tops getting bleached from growing into or too close to the light source. Most high powered LED grow lights deliver the best light quality and intensity from ten to twenty four inches from the tops of plants. Keep this distance in mind when planning vertical space use for your hydroponics system.
Nutrient Solution Reservoir
The tank that holds, catches, and recirculates the hydroponic nutrient solution should be sturdy and constructed of materials that do not react with plant nutrient solutions and/or leech unwanted substances into the nutrient solution. Purpose made hydroponic reservoirs fit these criteria. They are designed to hold larger volumes of solution while remaining low profile, to conserve vertical height for plants. For a 3’ x 6’ horticultural tray, a minimum reservoir capacity of 35 US gallons is recommended. Larger volumes are preferred, as the solution chemistry will fluctuate less quickly as water and nutrients are used up by plants.
A float valve is worth its weight in gold for growers when installed into the hydroponic reservoir. Using a very low volume pump or simple gravity, fresh water is added to the reservoir as it is used by the crop. This keeps nutrient solution composition stable and eliminating the need to manually add water daily. Better growth and less work can be had for less than ten dollars by adding a simple float valve to the hydroponic reservoir.
Plants tend to perform best when the nutrient solution is aerated. A steady stream of air bubbles in the reservoir helps keep the nutrient solution mixed while adding some oxygen to help supercharge water and nutrient absorption for plant roots. Saltwater aquarium air stones and ¼” tubing is inexpensive and easy to work with. A large single air pump with adjustable outputs on a manifold is a good choice versus a single air pump for each reservoir. Air can travel easy in simple ¼” tubing over distances. Having one central air pump allows you to aerate your water holding tanks and multiple reservoirs with ease.
In most instances the hydroponic grow room will be warm enough for the nutrient solution to remain above 65 degree Fahrenheit continuously. A grounded submersible aquarium heater might be added to the nutrient reservoir and water holding tank in a greenhouse or in colder climates.
TIP: Cannabis plants will tolerate lower than optimal air temperatures if the roots are kept slightly warmer (i.e., heated nutrient solution). Heating nutrient solutions above 80 degrees Fahrenheit is NOT recommended. This lessens the ability of the nutrient solution to hold valuable oxygen for roots.
Rockwool or coco pots and cubes typically will not require a reservoir chiller because they remain at ambient temperature or below in the growing environment. Gas charged water chillers or cooling coils are usually used where solution temperatures can rise above 80 degree Fahrenheit. In our hydroponic crop systems, the reservoir is below the horticultural tray(s) and does not get exposed to strong light so should stay in the optimal temperature range, which is 65 to 75 degrees Fahrenheit. Insulating and covering reservoirs is the first line of defense in keeping the nutrient temperature from rising above optimal. However, in some rare instances, a reservoir chiller may be necessary.
Magnetic drive pond pumps are well suited to hydroponic growing. Whether using the horticultural trays as a drip system or for flood and drain methods. The pump should be able to fill the table to your desired depth (usually two to three inches deep of nutrient solution) within a few minutes for flood and drain systems. A Mag Drive Model 3 is usually fine for a 3’ x 6’ flood table.
In drip systems, the pump needs to work harder because there are more tubing and smaller diameters of it to offer resistance. A Mag Drive Model 6 should suffice for a 3’ x 6’ drip table.
Any water pump you use should not react with the nutrient solution. So, unless the pump is stainless steel, avoid using metal pumps or pumps with non stainless steel parts. Usually, pond pumps will not react with nutrient solutions. The pump must be properly grounds and approved for submersible use. If you wish to keep your pump outside of the nutrient reservoir external line pumps may be used.
Whether you operate the horticultural trays with flood and drain or as a drip system, your irrigation cycles will need to be controlled by a timer. The timer should be easy to program and have a battery backup built in (versus line voltage only). In flood and drain systems, the pump will usually need to come on up to twenty four times per day for 5 minutes of “ON” time each cycle.
In drip systems, the pump may need to turn on from 24 to 96 times per day. An inexpensive grounded programmable digital timer that allows “timed cycles” is often the best bang for the buck. For example, you can program the ON time and OFF time in whatever increments you desire, and the cycle will repeat continuously, for example 5 minutes ON and 2 hours OFF (flood and drain). More sophisticated timers will allow you to program different day/night repeating cycles.
Irrigation Manifold or Plumbing
Your plumbing pipes feeding hydroponic plants should be free of metal parts or fittings and be chemically inert. This means they will not create adverse reactions when they encounter the hydroponic nutrient solution which by nature is mildly saline and acidic. Flexible poly pipe, ABS or rigid PVC pipe and fittings are inexpensive, easy to work with and do not typically cause any adverse reactions with plants or hydroponic nutrient solutions. Use ¾ inch or 1 inch diameter pipes and fittings for the main lines for 3′ X 6′ horticultural trays. Set drip tables up with 1/4 inch line for individual plant feeding. Flood and drain set ups require less tubing and fittings, taking less time and money to set up. Flood and drain tends to be more reliable and is less prone to clogging.
Drip systems will require an inline filter after the pump to help prevent clogging of ¼ inch lines and emitters. Also required is drip stakes and a “bubbler header” available from irrigation suppliers or from hydroponic outlets, i.e., “flora flex systems”. Flood and drain systems will require special flood and drain fittings, i.e., a taller riser to control the depth in the flood tray, and one for filling and draining (as activated and deactivated by the pump and timed cycle).
We recommend a Ground Fault Interruption (GFI) circuit for all electrical components that encounter the nutrient solution. Should something electrical become faulty while you are working with the nutrient solution, a GFI outlet can save your life.. Water and electricity do not mix.
Growing Media & Containers
There are a lot of choices for growing mediums for your hydroponic system. So, of course there is also a lot of good debates about why one type or style is better than another. We recommend using horticultural grade water absorbent rockwool flock. It can be used to fill any size of container because it is inexpensive and lightweight when dry. Rockwool flock is very flexible for the grower. Loose flock is 100% sterile and will contain no pathogens or pests. It comes from the manufacturer with a high grade of consistency. So the bale of loose flock you buy today will behave in the exact same way the one you buy three months later will.
Coco coir can also be effective, but it tends to be messier and has potential for contamination. Inconsistent in characteristics from batch to batch or from brand to brand have been found. Coir is a by-product of the coconut industry and is organic in nature. When preparing it for horticultural use it is often chemically treated. An additional advantage the rockwool has over coir is that a small amount can support a large plant. Proportionately you need less root space with rockwool to support heavy yields versus coco coir. Efficiency counts.