Self Watering Pots For Cannabis: Do They Work?
Quick answer: Yes, self watering pots for cannabis can work, as long as you use a light soilless mix, keep the reservoir filled and feed from the top rather than through the water. A reservoir in the base holds water that the mix wicks up to the roots, and an overflow hole on the side lets extra water escape. They suit growers who want steady moisture, but they still need daily checks in hot weather.
How a Self Watering Pot Works
A self watering pot is really two spaces stacked together. University of Maryland Extension says the growing medium sits on a perforated platform directly above a water reservoir, and that instead of drainage holes in the bottom, these containers have an overflow hole on one side. Roots grow through the medium and down toward the water.
Mississippi State University Extension calls these subirrigated containers. It says the potting mix pulls in moisture much the way a sponge pulls liquid from a pan of water, a process called capillary action. Water moves up into the root zone, which creates consistent moisture around the roots.
The overflow works like the overflow in a bathroom sink, Mississippi State says. When you fill the reservoir too high, the extra water runs out of the side hole instead of flooding the mix.
Are Self Watering Pots Good for Cannabis?
They can be, with limits. University of Maryland Extension says self watering containers help conserve water and nutrients and make it possible to leave your containers alone for a few days. That steady moisture comes in handy during hot spells and busy weeks.
The research behind these pots comes from vegetable and flower gardens, not cannabis trials, so watch your plants and the mix rather than a calendar. Mississippi State also notes that plants in subirrigated containers still need water as often as plants in regular containers. The difference is how the roots reach it.
Self watering pots are one choice among many. For size, material and drainage across all pot types, see our guide to the best cannabis growing containers.
What Potting Mix to Use
The mix has to carry water upward, so it matters more here than in a regular pot. Mississippi State recommends a soilless mix made from ingredients such as peat moss, pine bark, coir, vermiculite and perlite. It warns against native soil and bagged products meant for amending garden beds, because their physical properties do not suit subirrigated containers.
Mississippi State also says wetting agents, often found in commercial container mixes, improve how well the mix takes up water. Illinois Extension’s build directions call for a lightweight container potting mix.
How to Set Up a Self Watering Pot for Cannabis
- Choose bought or homemade. University of Maryland Extension says a number of commercial models are available, or you can make your own from a 5 gallon bucket. Illinois Extension has directions for a larger tub build.
- Check the overflow hole. Illinois Extension places the overflow hole about 3 to 4 inches from the bottom, below the top of the wick but not so low that the container holds too little water.
- Fill with a light, moist soilless mix. University of Maryland’s bucket garden starts with about 4 gallons of moistened medium. Pack the wick area so it touches the water.
- Plant and water from the top at first. Water the surface after planting so the mix is evenly moist and young roots settle in before they reach the wicking zone.
- Fill the reservoir through the fill tube. Add water until it starts to run out of the overflow hole.
- Add fertilizer on top of the mix. Mississippi State recommends placing granular fertilizer in a narrow band on top of the growing medium, following the product label.
- Check the reservoir every day in hot weather. Mississippi State says that if the reservoir dries out, capillary action stops, so it is important to fill the reservoir each day.
- Watch the plant, not the calendar. University of Maryland says its bucket garden needs water every day in July and August in full sun, taking 1 to 2 quarts a day.
Feeding in a Reservoir Pot
Mississippi State does not recommend adding water soluble fertilizer to the reservoir of a subirrigated container. It says this could raise soluble salt levels in the reservoir that burn plant roots. Instead, it recommends granular fertilizer in a narrow band on top of the medium, which releases slowly as water is drawn upward. It also says never to mix the fertilizer into the potting medium.
Mississippi State’s warning is about soluble salts building up around the roots. Our guide to salt buildup in cannabis soil explains how to spot and manage that.
When a Self Watering Pot Is the Wrong Choice
A self watering pot is not ideal if you want to give plants frequent liquid feeds, since the reservoir is not the place for soluble fertilizer. It is also a poor fit for garden soil, which Mississippi State rules out for these containers. If you like to water from below in a regular pot instead, see our guide to bottom watering cannabis.
Troubleshooting
The top of the mix stays soggy. Check that the overflow hole is clear and sits below the top of the wick, as Illinois Extension describes. A heavy mix can also hold too much water, so swap to a lighter soilless mix. For signs that roots are staying too wet, see our guide to overwatering cannabis.
The top is dry but the reservoir is full. The mix may not be wicking. Make sure the wick area is packed with mix and touches the water. Mississippi State notes that wetting agents help a mix take up water.
A crust forms on the soil surface. Minerals can collect where water evaporates. Avoid soluble fertilizer in the reservoir, as Mississippi State advises, and use granular feed on top of the mix instead.
The plant wilts on hot afternoons. The reservoir may be running dry. Mississippi State says capillary action stops when the reservoir dries out, so check and fill it every day in heat.
Roots grow down into the reservoir. University of Maryland Extension says roots grow through the medium and into the water in these containers, so this is expected. Keep the reservoir topped up so those roots stay in water.
Sources
- Mississippi State University Extension, Subirrigated Containers for the Mississippi Gardener (P2971): https://extension.msstate.edu/publications/subirrigated-containers-for-the-mississippi-gardener
- University of Maryland Extension, Self Watering Containers: https://www.extension.umd.edu/resource/self-watering-containers
- University of Maryland Extension, Types of Containers for Growing Vegetables: https://extension.umd.edu/resource/types-containers-growing-vegetables
- University of Illinois Extension, Make Your Own Self Watering Container (PDF): https://extension.illinois.edu/sites/default/files/self_watering_container_directions.pdf
FAQ
Do self watering pots and autowatering plant bases work for weed?
Yes, if they are set up well. University of Maryland Extension says self watering containers help conserve water and nutrients and let you leave containers alone for a few days. Use a light soilless mix, keep the reservoir filled in hot weather and feed from the top. Watch the plant, since the research comes from vegetable gardens.
What does the overflow hole do in a self watering pot?
It lets extra water escape so the reservoir cannot flood the mix. Mississippi State University Extension compares it to the overflow in a bathroom sink. Illinois Extension places the hole about 3 to 4 inches from the bottom, below the top of the wick but high enough that the container still holds a useful amount of water.
How often should you refill a self watering pot?
Check it every day in hot weather. Mississippi State says that if the reservoir dries out, capillary action stops, so it is important to fill it each day. University of Maryland's bucket garden needed water every day in July and August in full sun, using 1 to 2 quarts a day.
Can you put nutrients in the reservoir?
Mississippi State University Extension does not recommend it. It says water soluble fertilizer in the reservoir could raise soluble salt levels that burn plant roots. It recommends placing granular fertilizer in a narrow band on top of the growing medium, where it releases slowly as water is drawn upward. Follow the product label for amounts.
What size self watering pot suits a cannabis plant?
There is no cannabis specific figure from Extension. As a guide, University of Maryland Extension suggests a minimum of 8 to 10 gallons of growing media, with a depth of 12 to 16 inches, for large vegetables such as tomatoes. A full size cannabis plant is closer to that group than to small herbs.
