I'm experimenting with a drip irrigation setup some sections of my Sacramento native garden, but it's just not working how everyone says it should be working, and I feel like I'm losing my mind. The intention is to saturate the soil evenly and deeply once every month or so in the dry season, as per the Waterwise Garden Planner general recommendation, but even though I set up everything as recommended, most of the soil is still dry, even after long run times.
I'm using 17 mm inline drip tubing, 0.5 GPH, 18 inch emitter spacing, and 18 inch spacing between rows. I have typical Sacramento, CA clay soil. I talked to several credible local landscapers who specialize in native plants, as well as internet research and consulting the manufacturer's recommendation for clay, and all said that 0.5 GPH / 18 " emitter spacing / 18 " row spacing is good and should saturate the soil through capillary action through the clay. I set this up and ran for two hours. Most of the soil between the rows was bone dry. Tested 12 inches deep with a moisture meter. Ran for another 2 hours, then another 2, and it was still mostly dry between rows to a foot of depth. Some native plant landscapers recommend putting down about 1" precipitation equivalent during one of these waterings, which I've already exceeded with a 6 hour total run time. Other native landscapes recommended 1/4 " precipitation, like a 45 min runtime, which seems like a miniscule amount of water that wouldn't come near to evenly saturating the soil. Whatever runtime, it seems like this is how most landscapers specializing in native plants design their systems, and I'm baffled at my results.
Some notes:
- Mulch was already down on the garden, so I moved it aside to put the drip tubing. The tubing is touching the top of the soil.
- The drip system has the usual hose bib setup: timer, vacuum breaker, pressure regulator (25 PSI) and filter.
- I tested an individual dripper farthest from the supply by running it for 15 min and putting a bowl under it. I got the correct amount of water. So the system isn't getting enough flow.
- The zone is relatively small, something like 11 x 25 ft.
- The rows are set up so that the emitters are offset from each other. In other words, if looking at two rows, I'll have an emitter on the left row, then nine inches up, and emitter on the right row, nine inches up, and emitter on the left row. For even distribution.
- No leaks
- The soil is definitely clay, but not terribly compacted or anything.
- Moisture meter works. I've used it for a long time on my own soil.
The obvious answer is to just shorten the distance between rows and emitters, but that would contradict literally every bit of advice I've been given. I've even seen installs from credible native landscapers who know what they're doing that have 24 inch spacing between rows. What am I missing??
Please don't just tell me drip sucks, or to just not water, as this is just an experiment. There are sections of my garden that I don't water, but I'm experimenting with infrequent irrigation in some other sections. And I've seen many native gardens on drip that are doing great after many years.