More Effective Raised Bed Drip Irrigation Techniques

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At the top of the page: an excerpt of a conversation with Don Shor of Redwood Barn Nursery about growing tomatoes with drip irrigation in raised beds from Episode 288 of the Garden Basics with Farmer Fred podcast.

Another podcast episode that really delves into drip irrigation was Episode 227, Understanding Drip Irrigation”. That featured an in-depth chat with author Robert Kourik, who literally wrote the book about good drip irrigation techniques and equipment. Give that a listen.

Drip Irrigation Lessons Learned the Hard Way

After working with drip irritation systems in the garden for more than 40 years, consider this my “Lessons learned the Hard Way.”

Example One: my original raised beds, from the early ‘90’s featured three parallel drip lines with inline emitters running the length of a four foot wide bed. Also lacking: no individual on-off valves for each bed. All the beds were, in effect, running on a single circuit simultaneously. The irrigation was running for two to three hours a day, four or five days a week, to achieve plant growing success.

The problem was the lack of water during a single irrigation flowing from the one-gallon inline emitters spaced 12 inches apart, on lines that were 18 inches apart in the raised beds. Complicating the matter: no attention was given to the cross-spacing of the emitters between lines. If all the emitters were lined up like little soldiers on those three lines, there were large areas of soil that had a hard time getting water.

The biggest lesson I’ve learned about raised bed gardening is something that Don Shor of Redwood Barn Nursery has pounded into our heads for decades: you have to consider a raised bed as just a large plant container, with all the limitations involved of dealing with potted plants:

• It dries out quicker.

• Drainage could be problematic.

• Tall plants, such as corn, tend to fall down and go boom much more readily in a raised bed than in an in-ground planting during a summer windstorm. A couple of reasons for that: the raised bed soil is not very good at anchoring roots. The water pattern in a raised bed does not encourage a wider plant root system. Roots will follow the water, not vice-versa.

Water tends to go straight down in a raised bed instead of spreading out, due to a higher content of loose, friable, potting mix-like sandy soil. In the backyard garden, there is probably a higher content of clay, which allows water to spread out. For example, in a freshly filled new raised bed with a premium potting mix, the water released from a drip emitter may only have a diameter of 8 inches across, as it descends through this mix.

In your backyard soil, that probably has a lot more clay? That water diameter may spread out 18 inches as it trickles downward.

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Cut Your Drip Irrigation Woes with These Tips

The solution? Add more parallel lines. Add mulch.

Solution number two: Stagger the lines so that emitters were not side by side.

But there was one more trick to employ to help preserve soil moisture: grind up fallen leaves from neighborhood oak trees, and use it as a mulch, several inches thick, year round.

Mulch, as I have reminded you for decades:

• Retains moisture.

• Keeps soil temperature constant, reducing plant stress.

• Suppresses weeds.

• Gradually increases soil organic matter, feeding the soil.

• Attracts beneficial organisms that improve soil fertility and porosity.

• Encourages healthier plants, reducing the needs for pesticides and fertilizers.

• Protects roots and plants from mechanical injury.

• On hillsides and around rural homes, certain mulches can suppress the spread of brush fires.

One solution occurred to be early on in my adventures in drip irrigation of raised beds. Using 4’x5’ sheets of concrete reinforcement screening, with six inch mesh spacing, to keep the dogs and cats out of the raised beds.

Note as well that even though you can bury the in-line emitter drip tubing beneath the mulch, I like to keep the end caps visible. That’s a reminder to occasionally undo them and flush any debris or impurities out of the lines.

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Fred Hoffman is also a University of California Cooperative Extension Master Gardener in Sacramento County. And he likes to ride his bike(s).

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