Guide to Automatic Watering for Indoor Cannabis

Guide to Run and maintain an automatic drip system

This article covers everything you need to know to run an automatic watering system for indoor cannabis. We explain the best type of automatic watering systems for fertigation (adding fertilizers to the irrigation water). We also discuss how to ensure proper water distribution with automatic watering to prevent nutrient burn. Bacterial infections are a common problem with automatic watering systems. We explain how to prevent bacteria in hydroponic reservoirs by managing temperature, oxygenation, the use of anti-bacterial products like Hydrogen Peroxide and beneficial bacteria products like Hydroguard. We provide specific advice about topping off and cleaning out the reservoir. Finally, we discuss how to control the quantity of water and the frequency and timing of events.

Setting up an Automatic Watering System is an excellent idea to help you to fertigate most efficiently. We have complete plans and instructions to build your own “DIY Automatic Watering System”. Whether you follow our plans or use a different system, the guidelines here will help you to avoid the common problems and make the most out of auto-watering cannabis.

The Best Automatic Watering System for Cannabis Fertigation

There are several different types of automatic or self-watering systems for plants. Broadly speaking they can be grouped into three types: Top-feed, Bottom-feed, and Wicking. In addition, systems can be set up for recirculation or “drain to waste”. It is important to be aware of how you are irrigating or fertigating your plants in order to choose the correct automatic watering system for your grow.

Top-Feed, Bottom-Feed, or Wicking Irrigation Systems?

If you are fertigating your plants (adding nutrients to the irrigation water), then many of the systems sold for houseplants will not work for your cannabis grow. Systems that work by wicking water through capillary pressure, such as Blumats, cannot be used with anything other than plain water. They are designed to simply keep the media moist and cannot produce run-off. If you add nutrient solution to blumats it will burn your plants and clog your blumats! You cannot fertigate with wicking irrigation systems.

For automatic fertigation you need to use either a top feed or a bottom feed system. With a bottom feed system, the containers are flooded from the bottom and water is distributed through the media primarily through capillary pressure (wicking). Because bottom feed relies on wicking, the distribution of the water is often sub-optimal. Furthermore, with no water running down through the media, salts can accumulate and lead to nutrient burn.

Use Top-Feed Irrigation Systems for Cannabis Fertigation

Top-feed irrigation systems are the best for fertigating cannabis. In a top-feed system water is added to the top and is distributed through the media primarily by gravity. This most closely resembles the way you would hand-water your plants. You can control the quantity applied and produce run-off at each fertigation event.

As I describe in our cornerstone article “Principles of Fertigation”, run-off removes excess salts and helps to prevent nutrient burn. During each fertigation event, about 20% of the water that you apply should flow through the container and end up as run-off. This is only possible with a top-feed irrigation system. Because of the benefits of run-off, we recommend top-feed irrigation systems for fertigating cannabis in soil, coco, or other hydroponic media. We provide plans for a top-feed irrigation system in our “DIY Automatic Watering System” tutorial.

Recirculation or Drain to Waste?

In a recirculation system the water is recirculated to the plants several times. In contrast, a Drain to waste system uses the water once and any run-off is disposed as waste water rather than reused for the crop. Drain to waste may sound wasteful, but it provides several advantages particularly in media like coco or soil.

Drain to waste style fertigation provides a more consistent nutrient solution to the plants. As I describe in our tutorial “How to Mix Nutrient Solutions for Cannabis”, there are several dimensions to a well balanced nutrient solution. It should have the correct electrical conductivity (EC), the correct Nutrient Element Ratio (NER), and the correct pH. We are able to set each of those to be ideal when we mix fresh nutrients. However, as the nutrient solution interacts with the plant, the media and the environment, the EC, NER and pH all will change. This means that once it is used the solution is no longer ideal.

Recirculation systems work well with deep water culture. With a recirculating deep-water culture set up, there is no media beside the water itself and the system is largely sealed to prevent evaporation except through the plant. The nutrient solution will still change through time, but those changes can be managed.

Use Drain to Waste Irrigation for Cannabis in Coco or Soil

Recirculation systems really do not work if the media is coco or soil. In both of these media, the interactions between the nutrient solution and the media is significant and renders the nutrient solution sub-optimal for continued use. In coco, in particular, recirculation systems are difficult. This is because the coco will take a share of the calcium and magnesium and replace it with potassium. Reusing that water will provide insufficient calcium and magnesium and excessive potassium. The potassium overdose can then actually lockout the remaining calcium and plants will suffer quickly. In addition to these changes in the NER, the pH will fluctuate as it passes through coco making it very difficult to maintain pH in a recirculation reservoir.

Drain to waste avoids these issues and delivers plants a perfectly balanced nutrient solution each and every time. The downside to drain to waste is the waste water itself. Fortunately, automatic watering systems allow you to fine tune water delivery and reduce the quantity of run-off that you will produce. However, you will produce run-off. To be fully automated, you will need an automatic drainage system in addition to an automatic watering system. We offer plans for an effective DIY Automatic Drainage system with our “Self-Draining Saucers” and “Automatic Pumping Drain Bucket”.

You should take responsibility to use or dispose of waste water properly. The best use for hydroponic waste water is to feed it to other potted plants. For additional ideas and considerations please read our tutorial “How to Dispose of Waste Water”.

Managing Automatic Watering Distribution:

When you add nutrients to the irrigation water (Fertigate), there are certain practices that you need to follow to avoid salt build-up in any media. As I discussed above, one key practice is to apply water until run-off at each event. Run-off removes excess salts and helps to prevent nutrient burn. The other key practice is to ensure that the entire volume of media is saturated at each fertigation event.

Saturating the full volume of the media ensures that there are no regions where salts can accumulate. When regions of the media do not become saturated they will wick moisture from the regions of the pot that are saturated. This can lead to salt build up in those drier regions which can burn your plants or create nutrient lockouts.

Distribution of water is rarely a concern when hand-watering. However, with drip irrigation systems that apply water in only a few specific locations it can be possible to get run-off without saturating the media. The water will follow well worn channels through the media and end up in the saucer even while regions of the media remain dry. The run-off EC in this situation is usually low, but the EC of the water available to the plant is spiking due to the concentration of salts in the drier regions. A plant that experiences nutrient burn despite low run-off EC is indicative of a water distribution problem.

There are several keys to manage water distribution with automatic watering systems. It is important to consider the devices you will use to deliver water and the containers that you are growing in. To make the water itself more suitable for automatic watering, we recommend using a wetting agent. Finally, it is a good practice to periodically hand-water which always ensure a complete saturation.

Water Distribution Options: Drippers and Halos

Good water distribution starts with the devices that you use to actually deliver the water to the plants. There are many options. Our “DIY Automatic Watering System” tutorial describes two different options for water distribution.

Drip Emitters: One option we describe is to use drip emitters that are common to outdoor drip irrigation systems. A benefit is that the parts are widely available, and the system is very scalable. However, distribution is often less than ideal. The water pressure in most indoor drip systems is not as high as normal water pressure. The drip emitters are designed for outdoor use on normal (full) water pressure. On their labels, there are pictures where it will look like they spray water around – but in most indoor systems, they will just leak. If they are adjustable, you will be able to control how fast they leak, but they will not really distribute the water. You need to distribute the water by adding at least four drippers per pot. You should distribute the emitters equally around the surface of the media.

Hydro Halos: The other option that we describe is for Hydro Halos. Until recently these were expensive, but they have become far more affordable. I switched from a drip emitter system to hydro halos and have been impressed with how much they have improved the distribution. I have been able to go several weeks without hand-watering and the plants remain vigorous and healthy. In my opinion, Hydro Halos offer the best solution for distributing the water in indoor drip fertigation.

The Best Containers: Pots to Use with Automatic Watering

To distribute the water efficiently, you need to also consider the containers that your plants grow in. The size, shape and material of the container are all important to make the most out of automatic watering.

Container size depends on the media that you use. In soil, the size of the container will limit the total size of the plant. However, in coco/perlite, the size of the container does not limit the size of the plant. Coco offers more root space and a healthier environment for roots, which means that containers can and should be smaller than comparable soil grown plants. Smaller containers are easier to saturate at each event than larger containers. They do need to be watered more frequently, but that is not a problem with automatic fertigation. For autoflowers and most photo-period plants in soil we recommend 5-7-gallon final containers. For Coco/perlite, we recommend 3-5-gallon final containers.

Container shape influences the way that water will be distributed during each event. It is far better to have containers that are tall and narrow rather than short and squat. With top-feed irrigation we depend on gravity to do most of the work of distributing the water. A tall narrow pot will be easier to saturate the surface and then the entire volume of the container will be saturated as the water moves down through the media.

Container material influences drainage and root health. Standard plastic pots with drainage only in the bottom are not designed for high-frequency fertigation. Fabric pots are far superior because the drain much better and keep roots healthier. They are also very affordable.

In my opinion, Air-pots are the best growing containers to use with an automatic watering system. They offer the best drainage and promote incredible root growth. Importantly for automatic watering, they are tall for their size which promotes the efficient distribution of water through the media.

3-Gallon Fabric Pot
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Three-gallon fabric pots are a great option to use with Autoflowers and Photo-period plants grown in coco/perlite with high frequency fertigation. They are inexpensive and will not require very much media. However you will need to fertigate frequently.

5-Gallon Fabric Pot
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If you are growing in soil, 5-gallon fabric pots are a better option. Plant size is limited by container size in soil, so using a larger pot allows you to grow larger plants. You can also use these 5-gallon pots for coco/perlite, however they are larger than necessary.

#3 Air-pot
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I think these are the best container for growing in coco with an automatic watering system. They are a perfect final container for Autoflowers or Photo-period plants with less than a 6 week vegetation. You should expect to water up to 6 times per day with these.

#5 Air-Pot
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These are the containers that I am currently using. They are the reason that I recommend Air-Pots. The roots that plants grow in these pots are healthy and impressive. Air-pots are a little expensive compared to fabric pots, but I really think they are worth it. If you want to grow giant plants, these #5 air-pots are what you want.

Use Wetting Agents with Automatic Watering

Many growers are familiar with wetting agents primarily for use in foliar sprays. However, wetting agents can be beneficial in the nutrient solution as well. Wetting agents reduce the surface tension of water. That means that water will disperse better whether as a foliar or in an automatic drip system.

Irrigation water treated with a wetting agent will disperse laterally through the media much better than untreated water. This means that areas that are not directly under the dripper nozzles will still become adequately saturated. In addition, wetting agents help to prevent the dripper nozzles from clogging, which both ensures better distribution and prolongs the life of your system.

SM-90 is my preferred wetting agent because it also acts as an antibacterial agent. However, it is not currently available due to a labeling issue. The best replacement for SM-90 is Yucca Powder.

RAW Yucca Powder
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Yucca is an excellent wetting agent and there is evidence that it brings other benefits to the plant such as improved ability to handle climate changes and pathogen resistance. However, it is not an antibacterial. See below for how to prevent bacteria in your hydroponic reservoir.

Hand-Water Periodically to Prevent Salt Buildup

The final key to managing water distribution may be a periodic hand-watering. Hand-watering allows you to saturate the complete volume of the media and allow water to flow through regions of the pot where salt has been accumulating during drip irrigation. If you start to get tip burn despite the EC numbers staying within range, it is likely time for a hand-watering to flush those extra salts. Use a little more than the normal amount of water during this weekly hand-watering. This will act as a mini-flush that will remove salt build-up from areas that do not get much flow.

It can be easy to become complacent with an auto-watering system. However, you need to continue to pay close attention to your plants and hand-water when they need it. Now that I am using Hydro Halos, I have found that I can go several weeks without hand-watering my plants. However, when I ran drip emitters I would hand-water once every week.

Hand-watering when you clean out the reservoir is convenient. There will be nutrient solution left in the reservoir when it comes time to clean out. Plan this so that there isn’t a lot! I save this nutrient solution and use it to hand-water the plants. It is still clean enough to feed the plants, but I don’t want to put it back in the clean reservoir, so it is the perfect option for hand-watering. This accomplishes two things: It uses up the nutrient solution and it helps water distribution.

How to Maintain a Hydroponic Reservoir

Every automatic fertigation system has a reservoir with nutrient solution that becomes a prime breeding ground for anaerobic (bad) bacteria. Bacteria like Pythium can colonize the reservoir and eventually infect your plant. Pythium is the pathogen that leads to root rot.

Plants grown in coco do an excellent job fighting off Pythium infection. I have advised hundreds of coco growers and root rot is a very uncommon problem even when reservoirs are infected. However, it is always best to maintain a clean reservoir to provide the best water to the plants and reduce any risks of infection.

Use Antibacterial Hydrogen Peroxide (H2O2) or Beneficial Bacteria

If you are running an Auto-Watering System with a reservoir then you will need an additional product to help control anaerobic bacteria. There are two ways to handle this. You can go the sterile route and add Hydrogen Peroxide (H2O2) to the nutrient solution or you can add beneficial bacteria which will out-compete the bad bacteria. Both paths are viable strategies to limit anaerobic bacterial growth in your reservoir.

Hydrogen Peroxide 34%
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If you use H2O2 you should get high strength (28-35%) food grade H2O2. This is far stronger than the H2O2 used in First Aid, which is only 3%. You use 2.5ml/gal. Add it last, just prior to adding the nutrient solution to the reservoir. It does not affect EC or pH.

We recommend purchasing H2O2 locally rather than online. It is available at better prices in most hydroponic stores. Most of the products available online are diluted to a 12% strength, however the product we link here is sold at the full strength of 34%. This is a strong solution and needs to be handled with care.

Botanicare Hydroguard
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Hydroguard is an alternative to Hydrogen Peroxide. Rather than killing all bacteria and creating a sterile reservoir, this product supplies an army of beneficial bacteria which will out-compete the bad bacteria.

Oxygenate the Water

When you keep nutrient solution in a reservoir it is important to keep the water oxygenated. Water with a high level of Dissolved Oxygen helps to prevent bad bacteria and is great for the plants. For small tanks, up to about 30 gallons, air-pumps and air-stones provide adequate oxygenation. If you run a larger reservoir or use organic nutrients then you should use a stirring pump to mix and oxygenate the solution. A stirring pump is a small fountain pump which should sit in the reservoir and run periodically to “stir” the nutrient solution.

Air Pump
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I use the hydrofarm air pump and it is perfect for most reservoirs. It is easily adjustable and plenty powerful for a reservoir up to 30 gallons.

Air Stone and Tubing
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Pawfly makes the perfect accessory kit to go with an air-pump. The kit comes with two air-stones, tubing and splitters that will allow you to use both stones with one pump and tube.

Stirring Pump
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A stirring pump is an alternative to air-pumps and air-stones. It is the preferred style of aeration if you have a large reservoir (over 30 gallons) or are using organic nutrients. Stirring pumps are small water pumps that sit in the reservoir and lift and stir the water. You can attach a small section of Poly tubing to the pump so that the water is lifted just above the surface of the water in the reservoir. Pumping the water just above the surface and allowing it to fall back like a fountain is one of the best ways to oxygenate water. If you use this “fountain style” aeration, then the pump should be run for a couple minutes every hour and prior to each fertigation event.

Electrolysis is Not a Viable Option for Oxygenation

Electrolysis is a third option to aerate the water, however, it is not a practical option for most growers. The electrolysis devices work by passing an electrical current through the water and separating the hydrogen from the oxygen. This produces water that is super-saturated with dissolved oxygen, which would be great. However, the devices are very expensive and are not designed to work in water with high levels of dissolved calcium. The calcium that we add to our nutrient solution will precipitate on the electrical probes and quickly reduce the efficacy of the device.

Chill the Reservoir: Ideal temperature range 65-68f; 18-20c

It is easier to oxygenate water that is cooler. Therefore, many hydroponic growers use chillers for their reservoirs. However, a chiller is not needed unless you have a large reservoir (>20 gallon) supporting a large number of plants. With smaller reservoirs, you can chill the reservoir the cheap and simple way. Simply freeze bottles of water and periodically drop them into your reservoir. This is a potential source of bacteria, so be aware of cross-contamination (keep your frozen water bottles clean).

Keep the Reservoir Covered and Protect It from Light

Bacteria needs light to grow, so if you keep the reservoir in the dark it won’t have much of a chance. The reservoir does not have to be light sealed, but the less light the better. Be sure to use a reservoir tank that is not clear or translucent. Place the reservoir in a location that will not receive a lot of light and keep always keep the lid on.

Monitor EC and pH in the Reservoir

The best way to monitor the health of your reservoir is to take regular readings of EC and pH. A bacterial infestation will cause pH to rise and EC to drop. If you notice this pattern in your reservoir, it is likely that you have a bacteria problem. If left alone, the reservoir will get slimy and start smelling like dead fish. The best way to get an early read on these issues is to monitor EC and pH in the reservoir. Since pH can potentially drift out of range, it is also important for plant nutrition to keep tabs on the pH in your reservoir.

You should adjust EC and pH issues to bring the reservoir back to your targets. But then look for the underlying issue. Ideally, the EC and pH in your reservoir should be stable.

  • To Adjust pH: Add pH up or down
  • To Adjust EC: Add stronger or weaker nutrient solution

Topping-Off and Cleaning-Out

As the plants use water and the reservoir level drops you need to know when it is safe to “top-off” the reservoir and when you need to clean it all out. Despite your best efforts, bacteria will eventually colonize your reservoir and all tanks should be periodically cleaned out. However, you can also safely top-off your reservoir between tank clean-outs. For most growers a good rule is to clean out the reservoir once per week.

How to Top-Off the Reservoir:

For up to a week, you can simply top-off the reservoir with fresh nutrient solution. You must mix this nutrient solution in a separate container and then add it to the reservoir. You cannot add water and then mix nutrients directly in the reservoir because this can lead to lockout. Always measure both the EC and the pH in the reservoir before adding top-off water. You should calibrate the EC and pH of top-off water to bring the reservoir back to your EC and pH targets.

Clean-Out the System Once per Week:

After a week you will usually start to notice the sights and smells of bacterial infection in your reservoir. Things start to smell a little fishy and you may notice a film on your air-stone or even floaters in the water. These are all indications that you need to clean out the system.

Hydroponic Reservoir Cleanout Procedure:

  1. Drain the reservoir of nutrient solution (usually safe to use for hand-watering)
  2. Remove the pump, air-stone, and thermometer probe
  3. Soak these in a solution of diluted H2O2
  4. Use H2O2 also to clean out the reservoir. Be careful, it will burn your hands. Use gloves!
  5. Rinse everything and reassemble

Quantity, Frequency and Timing

You need to dial in your auto-watering system to the needs of your grow. However, there are some general principles to help you control the quantity of water and determine the frequency and timing of the fertigation events.

Flow Rate: Your drip system must have some way to adjust the flow to individual plants. With the drip emitter system, you control flow by twisting the heads of the emitters. With the Hydro Halo System, you control flow with ball valves. If your drippers are not adjustable, you will need to add ball valves on each line to regulate flow.

Duration of Events: Once the system is installed, you should run it and wait for run-off. Run-off should appear from all pots at about the same time. Adjust flow to accomplish this. Note the time it took and establish fertigation event durations. Using a timer with one-second intervals allows you to precisely set the duration of fertigation events

Digital Timer with one second intervals
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This is the best timer for automatic watering systems that I have found. It allows you to set watering intervals in one second increments, which allows fine-tuning an automatic watering system.

Frequency of Events: The most important factor which determine the frequency of fertigation is the media in which you grow. In general, you cannot fertigate soil more than once per day. On the other hand, Coco/perlite does best with several fertigations per day. If you are growing in coco, please read our tutorial “How to Water Cannabis in Coco” which provides specific guidance for determining the best frequency and timing for your fertigation events.

Final Considerations:

There is one final aspect of automatic watering that bears mentioning. All of the plants that you put on the system will get the same nutrient solution. You can revert to hand-watering to do flushes when needed. However, you want to be able to give the same nutrient solution to all of your plants at every stage of the grow. This means choosing strains which enjoy similar EC and which will mature through the flowering cycle on similar timelines.

Automatic watering makes growing cannabis much easier. It takes a little work to get the system set-up, but it is well worth it in the time and energy it saves during the grow. If you follow these guidelines, automatic watering will go smoothly for you and your plants!

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