Drip Irrigation for Containers and Box Gardening
Container gardening with flowers and vegetables is great for adding design elements in the landscape, extending vegetable garden space, optimizing sun in a shady yard, and utilizing small spaces such as patios and balconies. At the same time growing in containers has its own challenges with soil, nutrients, and watering. Similar to container growing are box gardens for vegetables which uses a light weight soil and has nutrient and watering challenges.
From experience, I found a reliable drip irrigation system for each: dripperline for containers such as pots and half-barrels, and drip tape for vegetable box gardens. If you are interested, I carry all the supplies mentioned below. Please click here for an irrigation supplies catalog and click here for a current price list.
Watering Containers with Drip Irrigation
I have tried a variety of irrigation methods to water containers including sprayers and several types of emitters. My choice for containers 10” in diameter or larger is a loop of dripperline with emitters every 12”. The advantage is that the water is distributed evenly around the container and the growing leaves will not interfere with the watering like with sprayers. For more information click here for Basics of Drip Irrigation.
Dripperline is ¼” poly tube with emitters built in every 12 or 6 inches. I recommend the 12” spacing because 6” emitter spacing often delivers too much water too fast. For containers smaller than 10” diameter, a single low flow emitter is recommended.
Dripperline has emitters that are non-pressure compensated meaning that the flow from the emitters is variable depending on the water pressure which is typically between 15 to 30 psi. However, each emitter in the dripperline will flow at an even rate. This is in contrast to soaker hoses or laser drilled soaker lines that have inconsistent flow rates from one end of the tube to the other. Below is a table of dripperline flow rates at different water pressures.
Pressure Versus Flow
Pressure in PSI (Pounds Per Square Inch)
Flow in GPH (Gallons Per Hour)
How Many Emitters to Use in a Container?
The length of the dripperline with emitters every 12” will be determined by the size of the container. A 10” diameter container may only use a length of 2 emitters (2 feet.) The 24” diameter container may use 4 or 5 emitters (4 or 5 feet.) The number of emitters in the container will depend on the size of the container, what you are growing, how long you will be watering, and the environment of the containers. Containers in some shade will not need as much water as containers in full sun on a warm patio.
Installing your Drip Irrigation
The following are directions for setting up your drip irrigation system for containers using dripperline.
1. Attach to the water source
Two options exist to attach to a water source.
Attach a brass Y shut-off valve first. On one side attach the timer and drip system and use the other side for your garden hose. Since the shutoff valve is under constant pressure with the timer, do not use a plastic or zinc coated valve because they are likely to fail. Always use plumbers (teflon) tape on all connections and tighten with only enough pressure to stop leaks. Photo at right show full faucet assemble including shutoff valves, timer, pressure reducer, filter, and hose swivel attached to the submain.
Sprinkler system valve station
The valve station you attach to must be dedicated for your drip system. You cannot run both drip and lawn sprinklers on the same valve station due to the difference in timing for containers and lawn.
If you are using an existing system, select the sprinkler head connection closest to your containers to attach the drip system to and use pvc plugs to seal off the rest. Dig down to the pvc line and plug it there. Don’t just cap off the flex pipe or riser.
At your selected connection point, remove the sprinkler from the flex pipe elbow adapter and bring the end to the surface. If your sprinkler head was not attached to flex pipe, connect a length of flex pipe to the pvc that is long enough to reach the soil surface without kinking. The flex pipe should have 1/2” elbow adapters at either end.
To attach the pressure reducer, you will need to first put a thread adapter on the elbow at the surface. I use a brass bushing ½” female pipe thread x male hose thread. Photo at left shows full sprinkler valve assembly including flex pipe with elbow adapter, brass thread adapter, pressure reducer, filter, and hose swivel attached to the submain. This assembly should not be buried in the soil but can be lightly covered with mulch.
2. Attach the pressure reducer and filter
Attach the pressure reducer first then the filter. A 150-mesh filter is highly recommended even with household water. Using a filter and cleaning it occasionally will help to extend the life of your drip system. For irrigation water or secondary water, a large filter and more frequent cleaning is required.
3. Getting the water to the containers
Attach the ½” submain tubing to the filter with a hose thread swivel and run the submain near your containers. Close off the end with an end cap.
Assemble your supplies including dripperline, ¼” tubing, scissors or clippers, barb connectors, goof plugs, ¼” valves, and hole punch.
Punch a hole in the submain with a ¼” hole punch near the container. Using a ¼” barb connector, attach a length of ¼” tubing to the submain that is long enough to go to the rim of your container. Cut the ¼” tube a little long so that you can move the container around a bit.
Use another ¼” barb connector (straight or elbow) to attach the dripperline at the rim of your container.
Then plug the end of the dripperline with a goof plug. Loop the dripperline around the inside of the container with the emitters evenly spaced and stake it in place. If you have a young plant in the center of the container, position one of the emitters next to it.
4. Add a shutoff valve
Cut the ¼” tube in a convenient location and insert a ¼” shutoff valve. These handy valves will allow you to turn off the water to that container when it is not needed.
Watering groups of containers
Be consistent with the number of emitters you use in containers that are the same size under the same conditions eg., sun or shade. When watering several different size pots in different conditions, the trick is to have everything perfectly watered by the end of the water cycle. When testing your system for the first time you may have to add or remove a dripperline emitter in a container to get it right.
Watering small containers
Use individual emitters on the end of a ¼” tube for pots smaller than 10”. Use low flow emitters so small pots won’t be over watered during the same time period the other containers are being watered.
How long should you water?
Containers usually need short periods of daily watering and sometimes twice a day in midsummer. Too much water will cause nutrients to be washed away. How often to water depends on how quickly your soil dries. If you have one container that consistently dries quicker than the others, simply add more dripperline to it.
Watering Box Gardens with Drip Irrigation
Watering box gardens is similar to pots and other containers. The plants are usually space more closely than when planted in the open beds and light weight garden box soils may be used especially for intensive gardening.
When a light weight box soil mix is used, water will quickly go through the upper layers similar to containers. The difference is that usually the containers have adequate drainage holes that allow excess water to flow out. However, excess water in garden boxes with light weight soil mix on top of native clay soils or weed clothe will tend to settle in the bottom creating a saturated oxygen deprived condition that can destroy root systems.
The strategy for watering garden boxes is short, frequent, even watering. I have found that drip tape with emitters spaced 4” apart is ideal. Drip tape coupled with a timer that can be set for at least 2 waterings a day makes a successful combination.
When using drip tape to water intensive gardening boxes, use 2 drip tape rows of 4” emitter spacing per linear foot so that a 4” x 6” grid of emitters waters every square foot effectively, even around the edges. For garden boxes configured in rows, drip tape with 4”, 6”, or 8” spacing is also an excellent choice. In that case use one row of tape per row of vegetables.
The water needs to be on only for a short time, maybe 5 to 10 minutes. Check the soil at the bottom of the box for excessively saturated conditions. You may need to water more frequent short times than you are use to.
For more information on setting up a drip tape system for your garden boxes go to the click here for Drip Tape Instructions.
Great gardening! Kathlyn Collins