Soil Orders

With their limited root space, container plants need more water more often than in-ground plants. Micro-irrigation is a perfect solution. Drop by drop, day in and day out, automated micro-irrigation keeps the containers evenly moist. It is easily adapted to the plants’ needs. If you like to move containers about, simply insert a hole plug in any unneeded tubing and punch into the supply line elsewhere.

Due to their special watering needs, container gardens should always be on their own circuits. In many cases, you’ll be watering daily, instead of every two or three days, and for shorter periods than other gardens.

Generally speaking, one or two drip emitters per container are sufficient, although long flower boxes may require three or more, set at about 12-inch intervals. If misters are used, only one is needed per container. Low-flow (1/2-gph) emitters are preferred, so water is applied slowly to avoid overflow, and they should be pressure-compensating, especially if hanging baskets are used in the circuit.

Drip irrigation may be efficient, but without proper planning it is also highly visible. Try running the supply line along the periphery of the growing space and behind the pots or even under a wood deck. Vinyl tubing can be led up the back of the pots or even up through a drainage hole before being clamped into place with a small stake.

Rather than run a series of tubes up the back of the same container, use a section of 1/4-inch tubing for a lead-in, then bend it into the pot with an elbow. Place the tubing around the inside of the pot and insert in-line drip emitters about every 12 inches. Plug the end of the tubing with a hole plug or by inserting a drip emitter.

Watering hanging baskets requires more care. Run the line up the supporting structure in the least obtrusive spot, then across the top. Use 1/4-inch vinyl tubing if possible, because it is easier to hide. However, it cannot be used in more than 25-foot lengths (see Working With Vinyl Tubing), so 1/2-inch poly tube may be required as a lateral line. Special support clamps for vinyl tubing and 1/2-inch pipe make it easy to fasten them, without crushing, to posts or masonry.

After installing drip irrigation in containers, but before adding end-closure devices, turn on the water and flush the tubing thoroughly.

Caring for the System

Depending on conditions, micro-irrigation should be left on for an hour or two, the time needed to moisten the mix entirely. When water begins to run out of the drainage holes, turn off the system.

All container systems require adjustment over time. For one thing, as plants grow they require more water. You can leave the system on for a longer period, but that works only if the needs of all the containers increase at the same speed. Otherwise, replace selected emitters with ones that provide a greater flow rate, or add extra emitters.

Another change comes with the end of summer, when watering requirements are reduced. Turn on the system for shorter periods. If any containers still get too much water, clamp off tubing or remove emitters and plug the holes. Finally, in areas with freezing temperatures, drain the irrigation system in the fall. If possible, disconnect it and bring it indoors for the winter.

Number of 1/2-gph Drip Emitters per Container

Container Diameter Number of Emitters
Up to 6″ 1
7″ to 12″ 2
13″ to 18″ 3
19″ to 29″ 4
Over 29″ 1 for every 6″ in diameter