Fertilizer Application
Marijuana Horticulture
by Jorge Cervantes
Some varieties can take high doses of nutrients, and other strains grow best with a minimum of supplemental fertilizer.
Determine if the plants need to be fertilized: make a visual inspection, take an N-P-K soil test, or experiment on test plants. No matter which method is used, remember, plants in small containers use available nutrients quickly and need frequent fertilizing, while plants in large planters have more soil, supply more nutrients, and can go longer between fertilizing.
Visual inspection – if the plants are growing well and have deep green, healthy leaves, they are probably getting all the necessary nutrients. The moment growth slows or the leaves begin to turn pale green, it is time to fertilize. Do not confuse yellow leaves caused by a lack of light with yellow leaves caused by a nutrient deficiency.
Taking an N-P-K soil test will reveal exactly how much of each major nutrient is available to the plant. The test kits mix a soil sample with a chemical. After the soil settles, a color reading is taken from he liquid and matched to a color chart. The appropriate percent f fertilizer is then added. This method is exact but more trouble than it is worth.
Experimenting on two or three test plants is the best way to gain experience and develop horticultural skills. Clones are perfect for this type of experiment. Give the test plants some fertilizer, and see if they green up and grow faster. You should notice a change within three to four days. If it is good for one, it should be good for all.
Now, it has been determined that the plants need fertilizer. How much? The answer is simple. Mix the fertilizer as per the instructions and water as normal, or dilute the fertilizer and apply it more often. Many liquid fertilizers are very diluted already. Consider using more concentrated fertilizers whenever possible. Remember, small plants use much less fertilizer than large ones. Fertilize early in the day, so plants have all day to absorb and process fertilizer.
It is difficult to explain how often to apply all fertilizers in a few sentences. We know that large plants use more nutrients than small plants. The more often the fertilizer is applied, the less concentrated it should be. Frequency of fertilization and dosage are two of the most widely disagreed upon subjects among growers. Indoor containerized marijuana can be pushed to incredible lengths. Some strains will absorb amazing amounts of fertilizer and grow well. Lots of growers add as much as tablespoon per gallon of Peters (20-20-20) with each watering. This works best with growing mediums that drain readily and are easy to leach. Other growers use only rich, organic potting soil. No supplemental fertilizer is applied until a super bloom formula is needed for flowering.
Fertilizing plants in the ground is much easier than fertilizing containerized plants. In the soil outdoors, roots can find many nutrients, and fertilization is not as critical. There are several ways to apply chemical fertilizer. You can top-dress a garden bed by applying the fertilizer evenly over the entire area. You can side-dress plants by applying the fertilizer around the bases of the plants. You can foliar feed plants by spraying a liquid fertilizer solution on the foliage. The method you choose will depend upon the kind of fertilizer, the needs of the plants, and the convenience of a chosen method.
When using synthetic fertilizers, it is extremely important to read the label carefully, and follow the directions. The initials “WSN” and “WIN” that you may see on the label stand for water-soluble nitrogen and water-insoluble nitrogen. WSN dissolves readily, and it is considered a fast-release nitrogen source.
Use a siphon applicator – found at most nurseries – to mix soluble fertilizers with water. The applicator is simply attached to the faucet with the siphon submerged in the concentrated fertilizer solution with the hose attached to the other end. Often, applicators are set at a ratio of 1 to 15. This means that for every 1 unit of liquid concentrate fertilizer, 15 units of water will be mixed with it. Sufficient water flow is necessary for the suction to work properly. Misting nozzles restrict this flow. When the water is turned on, the fertilizer is siphoned into the system and flow out of the hose. The fertilizer is generally applied with each watering, since a small percentage of fertilizer is metered in.
A garbage can with a garden hose fitting attached at the bottom that is set 3-4 feet off the floor will act as a gravity-flow source for the fertilizer solution. The container is filled with water and fertilizer.
When it comes to fertilization, experience with specific varieties and growing systems will tell growers more than anything else. There are hundreds of N-P-K mixes, and they all work! When choosing a fertilizer, make sure to read the entire label, and know what a fertilizer claims it can do. Do not be afraid to ask the retail clerk questions or to contact the manufacturer with questions.
Once you have an idea of how often to fertilize, put the garden on a regular feeding schedule. A schedule usually works very well, but it must be combined with a vigilant, caring eye that looks for over fertilization and signs of nutrient deficiency.
Leach soil with 1-2 gallons of mild nutrient solution per gallon of soil every month. This is the best form of preventive maintenance against toxic salt buildup in the soil.