One of the best ways to fertilize a marijuana garden is through a fertigation system. Fertigation systems use injectors to draw a concentrated liquid fertilizer solution from a reservoir into a garden hose or drip irrigation system while you water. As the fresh water flows through the pipe or hose, the injector meters out a precise amount of fertilizer, assuring your plants receive the level of nutrients they need to flourish. Many types of injectors are available, but some work better for growing marijuana than others.
If you are planning to combine your fertigation with a drip system, be sure to select the appropriate sprayers or emitters. I recommend installing a filter between the the injector and the emitter to remove any undissolved particles which may clog the emitters. This is a greater concern with organic fertilizers, which are more likely to contain material that does not readily dissolve in water. If you are going to use organic fertilizers, consider using self flushing diaphragmemitters, which are less likely to clog. With good filtration, even home-made compost and manure teas can be injected without fear of clogging. If clogging becomes a persistent problem, consider watering by hand with a garden hose. Most synthetic fertilizers are fully water soluble. So a filter installed between the injector and the emitter should be adequate for any design.
Liquid organic fertilizers are usually not as concentrated as synthetic fertilizers. For this reason, you may want to consider an injector capable of mixing at ratios as high as 1:10.
Synthetic fertilizers are often sold in highly-concentrated solutions that will require lower mixing ratios. If you intend to use both organics and synthetics in your garden, you will need an injector with a wide dilution range, such as an MP feeder or a Dosatron. The alternative is to dilute the synthetic fertilizer in the reservoir before it is picked up by the injector.
Unfortunately, not all fertilizers can be used with a fertigation injector; but even some granular fertilizers can be dissolved in water and then injected. One of my favorite fertilizers, Maxsea, is a mix of organics and synthetics sold in a granular form. To apply, I mix sixteen cups of Maxsea into two gallons of hot not scalding water. I then use a paint mixer attached to a cordless drill to dissolve all of the fertilizer. Once you have dissolved the dry fertilizer into a highly concentrated liquid, you can then apply it with an injector at a ratio of 1:100. This is the strength the manufacturer recommends.
Hose-end mixers are often sold in conjunction with synthetic fertilizer products such as Miracle Grow. These offer a simple and low cost solution for feeding your plants with a garden hose. Some hose -end sprayers also have a female coupling nozzle for in-line use with a drip system.
Syphon Mixers, Brass and Plastic (Mazzie)
Syphon mixers are manufactured by several companies, and are always used for in-line mixing. These simple mixers use a venturi to create suction, which draws concentrated fertilizer solution up a thin tube from a concentrate tank. The fertilizer concentrate is then mixed at a fixed ratio with the water that flows to the plants. The downside of this system is that the ratio can not be adjusted on the injector.
Brass syphon mixers can be found in hardware stores or nursery supply shops for under $30. In my experience, Hozon syphons mixers are unreliable, with a functionality rate of about 50%. If you do happen to get one that works, it will function perfectly and deliver years of service. May the force be with you.
The Mazzie Injector is built of sturdy plastic and designed for administering a high volume of concentrate. This mixer can be installed in-line using PVC, and should be plumbed with a bypass valve. Mazzie units are more expensive than their brass counterparts but are simple to use and, in my experience, very reliable.
Mixer-proportioner units, or MP feeders, have long been used by guerrilla growers for metering plant food into water lines. MP feeders use an internal bladder consisting of a special replaceable plastic bag, and offer adjustable injection ratios from 1:30 all the way down to 1:200. Featuring a steel tank and sturdy plastic fittings, the Young MP feeder is the toughest on the market–virtually bullet proof.
Despite their rugged construction, these units are not very precise or reliable. Their achilles heal is the bladder which is easily damaged. Filling MP feeders with concentrate is a chore, requiring tools and a funnel. Installing a brass gate valve can simplify the process, but is an expensive addition. Unless you have bears that routinely visit your garden, MP feeders are not worth the trouble and expense.
The Ez-flow is a pressure driven injector that comes with its own concentrate tank. Ez-flow mixers have an adjustable dilution rate which is selected by a dial located on the tank. Mix rates are set at 1:100, 1:250, 1:500, and 1:1000. As lower settings are not available, Ez-flow is better suited for turf and lawn care than herbaceous annuals like cannabis. The dilution range is too high for most of the fertilizers used in growing marijuana.
Fluid Driven Proportioners
Several companies make commercial grade fluid driven mixers. These units use the flow of water to drive an internal hydraulic pump. Suction generated by the pump draws fertilizer concentrate from a reservoir and mixes it very precisely. Most of these units offer a wide range of easily adjustable dilution settings. Fluid driven units are designed for in-line use and require some plumbing for installation. This plumbing should always include a PVC, valve- operated bypass.
Dosmatic builds a full line of fluid driven injectors which range in injection and flow rating. Dosmatic even offers a unit capable of injecting two concentrates. Some Dosmatic units also offer an integrated bypass function built into the mixer.
Dosatron has been making injectors for 25 years and, like its competition, offers many units to suit a wide range of flow and injection rates. Dosatron is my personal favorite, and I have used them for many years. The Dosatron company offers great customer service, and will even rebuild and update older models.
Tefen, an Israeli plastics company, offers a fluid driven injector called the Mixrite. The Mixrite is comparable to the Dosatron and offers the same functionality. I have only met one marijuana grower who fertigates through a Mixrite, and he seemed very happy with it.
Injectors In Series
Some fertilizers comprise two or more components that should never be mixed together in concentrated solution. Mixing such liquid concentrates can create undesired chemical reactions, rendering the fertilizer or additive useless or even harmful. By using two mixers and two concentrate reservoirs, you can inject the incompatible components into your water lines separately. When installing injectors in series, build with PVC and include valves that allow you to bypass either one or both injectors. The plumbing is a little complicated, but makes perfect sense once you play with it a bit.
With any injector you choose, make sure it is high enough off the ground to fit buckets or reservoirs underneath. For Dosatron style injectors, be sure to mount the system securely to a fencepost, wall or other stable structure for strength.
Injectors for outdoor garden fertigation,