How to Water Cannabis Plants in Coco Coir

Watering cannabis in coco coir

How should you water cannabis in coco? This is one of the most frequent questions that we get. We argue that high-frequency fertigation is the best way to water coco. But, how much, how frequently, and what do you pay attention to? This coco watering guide answers all your questions about high frequency fertigation and how to water cannabis in coco. I provide specific advice about how much water for each event and discuss how to determine your coco coir watering frequency. I include a coco coir watering schedule to help you set the timing of multiple daily fertigation events.

Dr Coco’s Guide to Feed and Water Cannabis in Coco

This article is part of Dr Coco’s Guide to Feeding and Watering Cannabis in Coco. Be sure to read the complete series!

Feeding and Watering is "Fertigating"

When we water plants in coco, the water should always include nutrients. The technical term for this is fertigation, which simply means combining fertilizers with the irrigation water. Proper fertigation strategy is the key to getting the best results from your coco grow. In “Growing Cannabis in Coco with High Frequency Fertigation”, I lay out 5 key principles. In this guide, I explain how to put these principles into action.

Principle 1: Fertigation is a Balance: Proper fertigation strategy balances the Nutrient Element Ratio (NER), which controls plant nutrition and the Electrical Conductivity (EC), which controls osmosis.

Principle 2: Always Add Fertilizers to the Water: To maintain the balance between NER and EC, nutrients must be added to all irrigation water at the correct ratios and doses. The feed chart determines the ratio, and EC determines the dose. See our guide, "How to Mix Nutrients for Cannabis".

Principle 3: Keep the Coco Wet: Do not let your coco get dry! One of the key benefits to growing in coco is that it enables high frequency fertigation. This article discusses just how frequently it should be.

Principle 4: Run-off is Critical: Run-off carries away the excess salts and allows you to maintain a consistent root zone EC. Proper run-off practices are discussed below.

Principle 5: Manage Electrical Conductivity (EC): You need to monitor the EC of the nutrient solution you are adding (inflow) and the EC of the water that drains through and ends up in the saucer of each plant (run-off). As discussed in our tutorial “How to Manage Cannabis Fertigation by Measuring Run-off EC”, The critical number is the difference between the two. As explained below, fertigation frequency is one of the main ways that you maintain that difference in the acceptable range.

Coco Coir Watering Guide

This coco watering guide explains in detail how to put the principles of high frequency fertigation into action. It explains:

  • The basics of watering cannabis in coco.
  • How much water you need to apply.
  • How to determine your coco coir watering frequency.
  • The best coco coir watering schedule.
  • And, how to handle run-off water.

Watering Cannabis in Coco

Many growers are concerned about watering because of their experience with soil. Happily, coco is not soil and it is a lot easier to know how and when to water in coco than in other media. There are a few basic rules for watering the plants and they can be mastered quickly.

Ensure Complete Saturation

Every time you water cannabis in coco, you should saturate the entire volume of the media. Remember that even at the seedling stage there is no real risk of over-watering. Properly conditioned coco retains adequate oxygen for the roots even when it is saturated.

Saturation is important to prevent salt build-up in the media which can burn your plant. The water that moves through the media and ends up as run-off is the mechanism that prevents salt build up. If the media is not saturated, then there is no water moving through it and salts accumulate.

Water Quantity is Determined by Run-off

The number one rule for watering coco is that you should always provide enough nutrient solution to each plant to produce 10-20% run-off. That means that if you add one quart of water then 10-20% of that quart should end up as run-off. Run-off water plays an important role in maintaining healthy conditions in the root zone. Therefore, you need to always get run-off no matter how much water you must add in order to accomplish that.

Under high-frequency fertigation, the quantity needed to produce run-off should be small. As I explain in “Growing Cannabis in Coco with High Frequency Fertigation”, it is ideal to keep the coco between 90 and 100% saturated all the time. Therefore, when we water in coco, the coco is already 90% saturated and it cannot hold much more. As discussed further below, the ideal quantity of water per event is about 5% of the volume of the growing container. This is ideal, but the rule is that you need to always provide enough water to actually produce adequate run-off from each plant.

Hand-Watering vs. Automatic Watering for Coco Grows

Many growers are concerned that high frequency fertigation is only possible with an automatic watering system. However, it is possible to unlock the benefits of high frequency fertigation with only watering once or twice per day. Therefore, it is possible to get tremendous results from coco when hand-watering, but it requires a significant commitment.

Automatic watering systems are preferred because they make it very easy to manage your grow. Not only do they make it easier, but they allow you to set the best frequency and timing for the plants. Automatic watering is less expensive and easier to set up than most growers think. We have a complete series of articles and tutorials for setting up and running your Automatic Watering System.

The Coco for Cannabis Guide to Automatic Watering

Coco Coir Watering Frequency

Watering coco frequently is best. However, you should not continuously apply water with micro drip, wicking, or other such systems. Nutrient solution should be applied during events which saturate the media and produce run-off. After each event there should be an interval to air-out. The interval can be as little as 3-4 hours during peak needs.

There are three main ways to determine your coco watering frequency:

By Look and Feel:

The surface of the coco should never get dry! If you are familiar with growing in soil, you will certainly feel like you are over-watering in coco. When you are watering coco, it should still be moist from the previous watering. If the surface of the coco is dry, your coco watering frequency should be increased. The surface of the coco should never become so dry that it turns lighter brown.

By Volume of Water Needed:

Coco mixed with perlite has the ideal air to water ratio when it is 90%-100% saturated. This means that when the coco has lost 10% of the water that it can hold you should water again. Since water is about half the total volume of saturated coco, the amount of water required should be about 5% of the container volume.

As an example, in 5 gallons of media, it should take about 1 quart of water to achieve adequate run-off. This is less water than most growers assume. Quantities are small because frequency is high. Since you are never giving the coco an opportunity to dry out, there is never going to be much capacity for it to hold more water.

If it takes more than 5% of the container volume to produce run-off, it means that the coco has become too dry. The best remedy is to water more frequently. In coco, it is always better to err on the side of watering too much than not watering enough.

By Monitoring EC:

Early in the grow, you should use look and feel along with volume to determine your coco watering frequency. However, as the plant becomes established and is growing rapidly, you should also consider EC. Adjusting the frequency of watering is our best tool to control the EC in the root zone and provide plants the best possible growing conditions.

The EC/PPM of the water will rise as the water sits in the pots. When we add fresh water, it lowers the EC in the pot to the level of the inflow. If we wait too long between waterings, the EC/PPM in the pot may rise to dangerous levels and burn your plant.

In our tutorial, “How to Manage Cannabis Fertigation by Measuring Run-off EC/PPM”, I explain in detail how to use EC/PPM to manage your watering or fertigation strategy.

Start with Once or Twice DAILY Watering in Coco:

You should water cannabis in coco at least once per day. For this reason, it is important to always keep plants in appropriately sized containers. I start plants in pint sized containers. Initially, I water once per day, but will increase to twice per day while they are still in fabric seedling pots. You should only water seedlings that are in larger containers or plastic seedling pots once daily until the plant grows larger. Be sure to read our tutorial “Transplanting Cannabis Plants: Why, When & How”.

Fertigation at this early stage is difficult because the plant cannot tolerate high EC/PPM water, but the coco requires a large dose of CalMag. High frequency fertigation allows us to deliver a larger total dose of Ca and Mg to the coco while not burning the plant with high EC. Please read our detailed guide, “How to Grow Cannabis Seedlings in Coco Coir” for step-by-step guidance for watering during the seedling stage.

Increase Watering Frequency as the Plants Mature.

Twice daily watering is usually ideal through the transplant phase until the plants arrive in final containers. Once in final containers, watering frequency should be adjusted based on the factors discussed above. The plant's water needs increase during flowering and your coco watering frequency should increase as well.

Watering frequency will depend on plant size, container size, climate, lights, and relative humidity. Ideally, you should plan to water your cannabis plants in coco 3-5 times per day during the flowering period. In coco, the best results come from small containers with frequent watering. Three to five times per day may sound like a lot of water, but with such frequent watering the amounts required at each event are very small.

It is only possible to water 3-5 times per day if you have an automatic watering system. If you are hand-watering, you will probably be limited to twice daily watering. To compensate, you should use larger final containers. I explain this in more detail in our tutorial “Transplanting Cannabis Plants: Why, When & How”.

Coco Coir Watering Schedule:

I designed this coco watering schedule to help you set the timing of multiple daily watering events. For timing the duration between events, one hour of “lights on” is equivalent to two hours of “lights off”. Timing for these events works best as I show in the chart below.

Light Cycles and Coco Watering Schedule:

Your coco watering schedule depends on the light schedule that you are using. 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.

How to Handle Run-Off

The first rule about watering cannabis in coco is that each time you water there should be run-off. That run-off water plays a critical role in preventing salt build up in the coco. Because of this it is important to remove the run-off water quickly. It is also important to periodically measure the EC/PPM of the run-off water. This section of the coco watering guide explains what you should do with run-off water.

Remove Run-Off Quickly

As run-off emerges from the bottom of the pots, you should remove it as quickly as possible. It is important to have a strategy to remove the run-off water from the saucers. As I discuss in “Growing Cannabis in Coco with High Frequency Fertigation”, you should try to set up a run-off removal system that is easy on the plants and on you the grower.

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 Saucers”.

Measure the EC of the Run-off

Measuring and responding to run-off EC is the key to manage your grow like a pro. If you do not already have one, get a simple water quality tester. These meters make it easy to to measure the EC/PPM of the nutrient solution that you provide and the EC/PPM of the run-off water. To know how to respond to run-off EC numbers, be sure to read our tutorial, “How to Manage Cannabis Fertigation by Measuring Run-off EC/PPM

Measuring Electrical Conductivity

Measuring Electrical Conductivity (EC) is absolutely critical to managing your fertigation strategy and nutrient solution strength. The technology involved in measuring EC is rather simple which means that you do not need to invest in an expensive meter. 

EC/PPM Meter
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This is the meter that I use. I have verified its accuracy against other meters and it has served me well for more than 5 grows. For the UK and Canada, I linked similar models sold under different brands. The only drawback to these meters is that they do not calibrate for temperature. You should measure the water when it is at about the same temperature that it will be when applied to the plants (about 68f/20c).

Author: Dr Coco

I am a university professor and have taught courses in horticulture. I am coco for cannabis and I hope you are coco for cannabis too :) Grower Love!

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