How Frequently to Fertigate
There are three main ways to determine your fertigation frequency:
By Look and Feel
The surface of the coco should never get dry! If you are used to growing in soil, you will certainly feel like you are over-watering in coco. When you apply each fertigation, the coco should still be moist from the previous fertigation. If the surface of the coco is dry, fertigation frequency should be increased. If the surface of the coco becomes so dry that it turns lighter brown, the coco is dangerously dry and you are likely burning your plants with high EC.
By Volume of Water Needed
You should fertigate frequently enough that about 5% of container volume of water produces run-off. This is less water than most growers assume. Fertigation quantities are small because frequency is high. Since you are never giving the coco much time to dry out, there is never going to be much capacity for it to hold more. As an example, in 5 gallons of media, it should take about 1 quart of water to achieve adequate run-off. If more than 1.5 quarts are required to produce adequate run-off, fertigation frequency should be increased.
By Monitoring EC
Early in the grow, you should use look and feel along with volume to determine frequencies. However, as the plant becomes established and is growing rapidly, you can also consider EC. As explained below, when the difference between inflow EC and run-off EC becomes too large, increasing fertigation frequency is the preferred way to lower it. Obviously, there are limits to this, but mature plants are difficult to overwater in coco/perlite. See our tutorial, “How to Manage Run-off ECâ€.
Start with DAILY Fertigation
In coco, your plants should be fertigated at least once per day. It is important that they are always in appropriately sized containers. A specific transplant strategy is laid out in chapter 2. Starting in pint sized containers, small seedlings should be fertigated once per day. Once they move to half-gallon containers and become established, you can begin fertigating twice per day. In final containers, plants may stay at twice per day through the rest of the vegetative period or require 3x daily fertigation depending on container size, climate, lights, and relative humidity. Tracking EC and run-off will allow you to determine when to increase frequency.
During Flowering: At Least Twice Daily
Water needs increase and your fertigation frequency should as well. Plan to increase to 3-5x per day, depending primarily on container size. You can get away with twice daily watering in larger containers. However, in coco, the best results come from small containers with more frequent fertigation.
Fertigation Event Timing:
For timing fertigation events, one hour of “lights on†is equivalent to two hours of “lights offâ€. Timing for these events works best as I describe in the table below.
Light Cycles and Fertigation Timing:
The light schedule you are using needs to be considered when setting the timing of fertigation events. In the cannabis community, light timing is expressed as a fraction with “Lights on†time over “Lights off†time.
24/0: Lights are on 24 hours and off 0 hours
18/6: Lights are on 18 hours and off 6 hours
12/12: Lights are on 12 hours and off 12 hours. 12/12 timing is used during the flowering period with Photoperiod plants.
Fertigation Event Timing
How to Handle Run-Off
Remove Run-Off Quickly
As run-off emerges from the bottom of the pots, it should be removed as quickly as possible. If pots are allowed to sit in their own run-off, it will be reabsorbed into the coco. When this happens, salts will accumulate in your coco and quickly burn your plants.
I recommend using plant elevators to raise the pots within the saucer. This prevents the re-absorption of run-off and increases drainage and airflow. To remove the waste water from the saucers, I strongly recommend elevating them and installing drain lines. We have complete plans and instructions for making “DIY Self-Draining Saucersâ€.
Measure the EC of the Run-off
Reliable meters can be purchased for as little as $10-$20. I use this Hone Forest EC meter and I have verified it’s accuracy against other meters. The technology involved is simple and you do not need to invest in an expensive EC meter.
To know how to respond to run-off EC numbers, be sure to read our tutorial “How to Manage Run-off ECâ€.
Taken from cocoforcanabis. Website.
