Growing Cannabis in Coco Coir with High Frequency Fertigation

Growing Cannabis in coco with high frequency fertigation

Growing Cannabis in Coco

We argue that coco mixed with perlite is the best medium for growing indoor cannabis. However, coco is only a superior growing medium when it is properly prepared and managed. In this article, I address how to feed and water cannabis plants in coco. The key to unlocking the magic of growing cannabis in coco is practicing high frequency fertigation. Fertigation is adding fertilizers to the irrigation water. It is the way that we feed and water plants in coco. I lay out the key principles of high frequency fertigation in coco and explain how to feed and water cannabis plants to maximize growth and yield.

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

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

Coco Coir is a Horticultural Wonder

Coco coir has many properties which make it a horticultural wonder. It is easy to manage, offers plants excellent growing conditions, and does not interfere with nutrition. Among the most important horticultural properties of coco coir is its air to water ratio.

The Air to Water Ratio

Plant roots require both oxygen and water. If the roots are starved of oxygen, they will turn brown and die. Soil based growing media become oxygen depleted when they are saturated with water. This means that the roots are unable to get enough air for some time after each watering. Growers need to wait for soil to dry out before watering again because otherwise the roots will not get enough oxygen and they will die.

One of the miraculous things about coco coir, especially when its mixed with perlite, is that it is nearly impossible to over-water it. Unlike soil, coco maintains sufficient oxygen in the root zone even when it is at field capacity (completely saturated with water). This is due to the physical shape and characteristics of the coco fibers which retain air even when the media is saturated with water. As a result, we can keep the coco wet and not worry that we are drowning the plant roots. Indeed, in coco, when the media is wet, the air to water ratio is ideal.

Coco is Not Soil

The fact that coco retains enough oxygen when it is saturated largely eliminates the risk of over-watering. Because of this, coco is far easier to manage for new growers than many assume. In soil, it takes experience to know when to water. Plants in soil are moving between being oxygen starved after a watering and being water deprived as the soil dries between events. In coco, on the other hand, plants never need to suffer, and growers don’t need to worry about over-watering.  All you need to do is water frequently to maintain the perfect ratio of air to water all the time.

How to Grow Cannabis in Coco

In many ways growing in coco is like growing in soil. It almost looks like soil and we put it into pots just like soil. We water from the top, can stick stakes in the pots and do other things that are just like soil grows. All of this makes coco a comfortable and familiar media to work with. If you are just getting started, be sure to read our article, “How to Grow Cannabis Seedlings in Coco Coir

The main difference between growing in coco and growing in soil is the fertigation strategy. Growing in soil requires lower frequency fertigation because of the air to water ratio. However, in coco, we can ramp up the frequency and get truly explosive growth. Plants grown in coco under high frequency fertigation will grow as fast or faster than plants grown in any other medium. A well-managed coco grow cannot be beat.

Plants Grow Best Under High-Frequency Fertigation

Delivering fertilizers through the irrigation water is the most efficient form of fertilization. It allows growers to supply plants with the exact nutrients that they require in forms that are easily accessible. Plants do not have to invest energy to obtain the nutrients, which leads to more vigorous growth.

The air and water retention properties of coco enable us to practice high frequency fertigation. In horticultural science, high frequency fertigation is recognized as offering the best possible growth. It is defined as having fertigation intervals of less than 24 hours – or fertigating at least once per day. However, often the interval between events is only a few hours.

High-frequency fertigation with drain to waste allows growers to provide plants with the precise nutrition that they require and maintain tight control on the nutrient element ratio (NER), Electrical Conductivity (EC), and pH. Growers can consistently add fresh nutrient solution that is set to the ideal NER, EC, and pH. Plants grow best when conditions are consistent and high frequency fertigation provides the best method to maintain all those variables.

How Frequently Should You Fertigate?

Ideally, mature plants should be fertigated 3-5 times per day. This may sound daunting to new coco growers, but it does not need to be as tough as it sounds. Automatic watering systems make growing in coco with high frequency fertigation incredibly easy, but they are not required. If you are watering by hand, there are simple adjustments which allow you to fertigate only once or twice per day.

Fertigation frequency is related to plant and container size. In smaller containers, plants need to be fertigated more frequently because the media holds less water. In larger containers the fertigation frequency can be reduced because the media is able to hold a larger store of water for the plant. We have specific guidelines for determining the best fertigation frequency for your grow in our tutorial, “How to Water Cannabis Plants in Coco”.

Hand-Watering Cannabis in Coco

It is possible to practice high-frequency fertigation in coco when hand-watering, but it requires a commitment. Coco should not get dry; therefore, it is important to fertigate at least once per day. If you are hand-watering, you should think carefully about your ability to commit to once or twice daily fertigations. However, if you are willing to commit to at least once daily fertigation, you can start to unlock the magic of coco.

When hand-watering you should plan for a 5 or 7-gallon final container. These are large enough to allow you to maintain an acceptable EC and NER balance with only once or twice daily fertigation. If you can manage twice daily fertigation, then the 5-gallon final containers are best. If you think the most you can do is once daily fertigation, then use 7-gallon final containers. Be sure to read our article “Transplanting Cannabis Plants: Why, When, and How”.

Automatic Watering Systems

Automatic watering systems are an excellent idea and are almost required to increase beyond twice daily fertigation. It is only reasonable to fertigate 3-5 times per day if you have an automatic watering system installed. Automatic watering is easier and less expensive to set up than most growers assume. We have a complete “Guide to Automatic Watering for Indoor Cannabis”, which explains everything you need to know to set up and run your system. We also have plans and instructions to build your own “DIY Automatic Watering System”. It is not something that you need to start, but it is something to keep in mind.

The Principles of High-Frequency Fertigation

Effective fertigation is the key to maximizing the speed of growth and the size of harvests. Understanding the five key principles of high frequency fertigation will allow you to manage your coco grow like a pro!

Principle #1: Fertigation is a Balance

A tremendous amount of confusion exists in the cannabis growing community about how plants interact with water and nutrition. It is important to understand that although you mix the nutrients with the water, the plant takes them up separately. Water is pulled across root membranes through osmosis and nutrients enter the plant separately, through diffusion, passive transport, and active transport. The plant receives water and nutrients through different processes, and they must be balanced.

Osmosis and Electrical Conductivity (EC)

The plant receives water through osmosis. It does so by producing sugars in its roots which draw water into the plant. However, osmosis is affected by the salinity of the nutrient solution. When the water is salty, the plant must produce more sugars in its roots in order to draw the water in. Plants can do this up to a point, but if their water is really to salty then osmosis will actually reverse, and water can be pulled out of the plant.

The fertilizers that we add to the water are different forms of salts. If we put too many nutrient salts into the water, it becomes very salty and the plants will struggle to pull in water through osmosis. This is the main reason we must be careful with the total dose of nutrients applied. We limit the amount of nutrients, not because of the risk of nutrient toxicity, but because of osmosis!

Electrical Conductivity (EC), is a measure of how saline (salty) the water is. EC, PPM, and TDS are all different ways to express the same basic measurement. I explain all of the details of EC, PPM, and TDS in our article, “Understanding EC, PPM & TDS for Growing Cannabis”. Be sure to also see our tutorials, “EC/PPM Targets for Fertigating Cannabis” and “How to Manage your Cannabis Grow by Measuring Run-off EC”.

Nutrient Element Ratio (NER)

Cannabis plants do best when nutrients are provided at the correct Nutrient Element Ratio (NER) for each stage of growth. All cannabis feed charts alter the ratio of nutrient elements over the course of the life cycle. It is important to follow these feed charts to provide the correct NER for your plants. Good hydroponic nutrients are able to deliver the correct doses of all the required nutrients at a reasonable total EC. Be sure to read our article “Cannabis Fertilizers, Supplements, and pH”.

Balance Osmosis (EC) and Nutrition (NER)

When we mix nutrient solutions, we need to follow the feed chart recipes to arrive at the correct NER. The correct NER is important for plant nutrition. After mixing the solution we need to make sure the total mix is not too salty for the plant. We do this by measuring the EC. The correct EC is important because it affects Osmosis. Be sure to read our tutorial, “How to Mix Nutrient Solutions for Cannabis”.

When EC and NER are balanced, fertigation fulfills the plant’s water needs and delivers nutrients to the plant in their most easily absorbable form. The plant has access to everything it needs, all the time, at the correct ratios – and growth explodes!

To maintain the balance, nutrients must be added to all irrigation water at the correct ratios and doses. The feed chart determines the ratio of each nutrient, and EC determines the total dose. As the plant absorbs water and nutrients the EC and the NER both will change. Practicing high frequency fertigation allows us to keep it from drifting too far from the ideal.

Many of our fertigation practices are about maintaining this balance with the correct EC and NER in the root zone. Each of the following four principles of fertigation focus on a specific practice to maintain the EC/NER balance and create the ideal growing conditions for your plant.

Principle #2: Always Add Fertilizers to the Water

Many guides recommend alternating nutrient solution with “plain”, “pHed”, or “CalMag” water. Although this may help prevent over-ambitious growers from burning their plants, it is not the correct practice to follow in a carefully managed grow. For a variety of reasons, it is much better to fertigate with the appropriate ratio and strength of nutrition at every irrigation event.

Feeding Cannabis Plants in Coco

Plants need nutrients in order to complete photosynthesis and grow. In a soil-less media like coco, the plant takes nutrients directly from the water. Nutrients must be present in the water for plant nutrition to take place. Buffered coco is wonderful because it does not interact with the nutrients. You, the grower, can precisely control the nutrients that are available to the plant by providing the proper ratio of nutrients at every fertigation.

To learn more about fertilizers for growing cannabis in coco, read our articles:

Consistent EC produces the Best Growth

In addition to feeding the plant, providing fertilizer with each irrigation is the only way to maintain a consistent EC in the root zone. In every media, plants grow the best when the EC of the water in the root zone is in the correct range and consistent. On the other hand, If the EC is fluctuating then the plant must invest energy and resources to adjust to it.

As discussed above, plants draw in water from the media through osmosis. In order to pull water into their roots, plants must adjust the concentration of sugars in their roots so that it is higher than the EC of the nutrient solution.  When roots are exposed to alternating irrigations with nutrient solution and “plain” water, they deal with a constantly fluctuating EC. As a result, the plants are forced to adjust constantly. Those adjustments cost the plant energy that would otherwise have gone into plant growth. One of the key benefits of coco is that it is relatively easy to maintain a consistent root zone EC. All we must do is provide nutrient solution with the correct EC every time that we water the plants.

Principle #3: Keep the Coco Wet

Remember, coco is not soil. You are not going to overwater your plants in coco because it maintains an ideal air to water ratio. The rule with coco is you should keep it wet.

Maintain Saturation between 90 and 100%

Because coco mixed with perlite maintains oxygen even when saturated, the best management practice is to maintain the coco at 90-100% saturation. This means that we water frequently, but the amounts applied each time are small. We are simply “topping off” the pots, pushing out a little run-off and bringing the coco back to full saturation.

Maintaining the media between 90-100% saturated means that we should fertigate again when the media has lost 10% of the water that it can hold. To estimate this, you can assume that when coco is fully saturated, water is half the container volume. So, a 5-gallon container that is fully saturated has about 2.5 gallons of water. 10% of 2.5 gallons is one quart. So, if the media can hold more than one additional quart of water then it has become too dry. We have specific guidelines for determining the best fertigation frequency and quantity for your grow in our tutorial, “How to Water Cannabis Plants in Coco”.

Do Not Let Your Coco Get Dry

Many guides suggest that coco can be managed just like soil and that you can feed and water only once or twice per week. This is bad advice when you are fertigating. Infrequent fertigations starve the plant of water in two ways. For one, plants have less water because there is less water being added. However, the more dangerous aspect of infrequent irrigation is that the EC within media will spike.

Allowing the coco to get dry after fertigation creates significant problems for the plant. The EC of the water suspended in the media is always going up between fertigation events. This is because of transpiration and evaporation, which remove water faster than the plant can absorb the nutrient salts. As a result, when the coco gets dry the plant has a harder and harder time getting water that is increasingly scarce and salty.

Dry Coco Leads to High EC and “Nutrient Burn”

The increased salinity that occurs as the coco dries is a cause of the wilting and burned tips that are often known as “nutrient burn” or “nute burn”. The plant has a harder time getting water through osmosis because the EC is high. This produces symptoms associated with water stress such as wilting. In addition, the concentration of salts in the media can lead to a high concentration of ions in the leaves which can cause the common “tip burn”.

Growers are often confused how their plants can suffer from “nute burn” if the nutrient solution that they add (inflow) is not too strong. However, the EC of the inflow is only one factor that determines the salinity of the water that is available to the plant. Even if you have good targets for the EC of the nutrient solution that you provide, allowing the coco to dry out will cause the EC in the root zone to rise to unhealthy levels.

Principle #4: Run-off is Critical

When you add nutrient solution, you are adding both salts and water. As nutrient solution sits in the media, transpiration and evaporation remove the water but leave behind the salts. This causes the EC of the nutrient solution suspended in the media to rise gradually between fertigation events. To control the EC and to maintain the best conditions for the plant it is critical to always water with run-off.

Run-Off Removes Excess Salts

Run-off carries away the excess salts and allows you to maintain a consistent root zone EC. You can think of it as the new water is replacing and pushing out some of the old saltier water. The salts are more attracted to the water than they are to the coco. As a result, the excess salts will easily flush out with the run-off water.

Always Fertigate with 10-20% Run-Off

The best practice to maintain a consistent root zone EC is to fertigate frequently with 10-20% run-off at each event. When we say 20% run-off we are referring to the amount of water that you provide. In a 5-gallon pot, a typical fertigation quantity will be about one quart. 10-20% of that quart of water should come through the media and drain into the saucer or collection area. If there is no run-off, then you need to continue to add water to the top until there is. If run-off is insufficient, the salts will accumulate and the EC of the nutrient solution in the root zone will go up, potentially burning your plants.

Remove the Run-Off Quickly

If pots you allow pots to sit in their run-off water, it will be reabsorbed into the pot. Because the function of run-off is to remove salts, you always need to remove run-off from the saucer or collection area quickly.

There are different ways to handle removing the run-off.  I recommend that you set up a run-off system that is easy on both the plants and their grower. Moving the plants around is not a great for the plants and using a shop vac to suck out the water is too much work for the grower under high frequency fertigation. I use self-draining saucers, and I think they are the best solution for removing run-off water. Even if you are hand-watering, be sure to see our tutorial for making your own “DIY Self-Draining Saucers”.

Principle #5: Manage Electrical Conductivity (EC)

Managing EC is the key to unlocking the full potential of coco and achieving the best harvests. 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). The EC numbers are important to maintain the best range for the plant. However, we learn the most by paying attention to difference between the inflow and runoff EC.

Monitoring the EC of the run-off gives you advance knowledge of any salt accumulation problems before they affect the plant. Measuring the EC of the run-off during a fertigation is a close proxy for measuring the EC of the nutrient solution available to the plant. The EC of the run-off is usually slightly higher than the EC of the nutrient solution inflow. When this is the case, the run-off is doing its job. If the run-off EC number becomes too high, then you can take the appropriate remedial actions. In my tutorial, “How to Manage your Cannabis Grow by Measuring Run-off EC”, I explain how to use frequent fertigation and adequate run-off to control the EC of the nutrient solution available to the plant.

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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The meter that I use is pictured and linked for the US amazon. I have verified its accuracy against other meters and it has served me well for more than 5 grows. The UK and Canadian options are 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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