Sub-Irrigation: Low-Maintenance Hydroponics
Thinking about that summer vacation? Well, sub-irrigation—with its concealed water supply hydrating the growing medium—might be the key to some well-earned time off. Using this system, indoor gardeners can go for a week or more without watering...
Many indoor gardeners have their precious plants blooming in 3-gallon or 5-gallon plastic pots. With fast-growing plants needing drink up moisture under bright horticultural lights, growers have to water those pots three to seven times per week. Some even report watering twice daily. Either way, the time spent on this garden chore adds up quickly.
However maintenance could be drastically reduced, especially on hot summer days or under hot grow lights, if these gardeners used the same sized containers with sub-irrigation. Sub-irrigation containers—also known as self-watering pots—have a chamber of water under the soilless mix.
Small sections of growing medium reach down into the chamber and act as wicks. The entire container is then watered slowly and steadily through the absorption of the solution from below. As you can imagine, this simple concept allows for much lower pricing than more complex hydroponic methods. Also, there are no pumps to get clogged.
In my region, a local professional gardener has constructed an entire 4-foot by 8-foot garden bed with sub-irrigation. He fed and watered his crop each week, and beneficial bacteria, myccorhizae and enzymes were added to prevent rot-inducing organisms from setting up shop in the layer of water and nutrients under the soilless mix. Even with this minimal watering, plants were robust and the harvest was bountiful.
To accomplish sub-irrigation gardening at home, growers can either buy special containers made for the task or they can construct there own with materials from the grow shop and hardware store. Obviously, the prefab units are preferred for their ease of use and reliability, but many growers will want to build it themselves.
- Drill a couple of ½ inch holes into the side of your container, about three inches up from the bottom.
- Place the two rockwool cubes (pre-soaked) into the container.
- Pour in three inches of perlite, making sure the perlite is even with the rockwool cubes and the ½ inch hole.
- Place one end of the tube into the perlite, making sure the top end of the tube is above the rim of the pot.
- Fill the container with a potting mix that is appropriate for self-watering planters.*
- Fill the perlite layer with nutrient solution via the watering tube. Water will trickle out of the ½ inch hole when it is full.
- Soak the soil and add a healthy plant. Keep the plant watered by refilling every seven to 14 days, or as needed.
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Prefabricated sub-irrigation containers are even easier to use, and take only seconds to set up. These plastic containers have specially made inserts to create their water chambers.
The insert raises the soilless mix up off the bottom of the planter, allowing space for water or nutrient solution. Many of these containers have great conveniences like overflow holes to prevent overfilling and, similar to the DIY container, a tube for refilling the water chamber.
For growers who use sub-irrigation to cultivate culinary herbs, such as basil, rosemary or thyme, you will be impressed with the increase in those plants’ essential oils.
These containers create varying moisture zones in the soil, with roots growing in drier soil at the top, moist soil in the middle, and water in the sub-irrigation chamber. With these mixed moisture levels growers can inoculate the growing medium and the water chamber with high populations of microbial organisms.
As the roots grow into the solution, they are coated with microbiology—which seems to result in a direct increase in essential oils in herb plants. Of course, with increased oils you can also expect increased flavors and aromas.
Another advantage of sub-irrigation growing is a better breakdown of organic substances in the root zone. Many growers incorporate organic products such as kelp into their feeding regimens.
Plants cannot take up these organic substances directly; bacteria must break them down first. The sub-irrigation chamber is the perfect environment for this organic breakdown. If you are growing with 100% organic inputs, try using these techniques. You may find increased yield from better nutrient availability.
If you are growing mother plants, also called donor plants, these types of self-watering pots can be an ideal method of keeping the old ladies happy and healthy. Top off the pot once every week or two, and you won’t need any pumps or timers to irrigate them. Mother plants with a constant source of moisture often produce soft growth that is perfect for fast-rooting clones.
So, let’s look at the advantages of growing your prized plants in pots with pockets of water. The most obvious advantage is less watering, which gives you more time for other garden maintenance or, perhaps, a road trip. Increased oil gives you a high-value culinary crop.
And finally, drought-weary gardeners and organic gardeners can expect healthier plants with the possibility of heavier harvests.
If any of those sound good to you, try growing in a few sub-irrigation containers. You might like so much you’ll convert your entire garden. Check with your local hydroponics retailer for more details on the various sizes and brands available in your area.
My favorite mix for these containers, as well as other indoor garden applications, is a well-mixed blend of the following items:
- 1 part peat-based potting mix
- 1 part coir-based potting mix
- 1 part rockwool grow cubes
- 1 part large-grade perlite