Summer Deep Watering

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Summers are tough for a desert botanist. It pains my heart to look out across both our yard and the open desert and watch the native plants turning brown, dropping their leaves, and shutting down for the summer. I know that these plants have to do this just to survive the coming months of intense sun, 100+ degree heat, and no promise of rain for most of the year. Yes, the scientist in me knows that all these desert plants have adapted to this climate by taking an obligate summer sleep, designed by nature to slip into dormancy for the summer, and that shutting down is what allows them to survive the brutal summers here. But it hurts me, none the less.

This is a strategy used by plants from deserts around the world. When the soil is hot and dry, the plants sleep. When the soil is cool and wet, they wake up and grow. I know that I must resist the urge to keep their soil wet over the summer; I would not be doing them any favor to constantly water them, because soils that are wet when they are hot would only grow harmful bacteria and fungus that cause root rot, and deprive the roots of needed oxygen, especially when soils are hot. I would literally kill my native plants with kindness.

But wait–it’s not the water per se that kills desert plant roots in the summer; it’s continuous water in hot soil that kills them. So what if we could occasionally deliver the water down into a soil depth where the soil isn’t hot? Moisture in cool soil doesn’t grow root pathogens like it does in hot soil. An occasional summer thunderstorm can be a natural occurrence in the desert, and that doesn’t hurt the plants, because it is fleeting moisture, soaked up by roots, and quickly drying out; the soil will not be soaked again for many weeks or months. Infrequent soakings don’t create enough incubation time for big populations of harmful soil microbes to grow and cause root rot.

So here is a strategy to help native and other desert-friendly plants get through summer with less pain for them and for their human garden stewards: during the summer, deliver water deep into the soil occasionally with “deep water stakes”, soaking subterranean soils several feet below the surface where soil temperatures are much lower.

We decided to try this method when our 25-year old, 15-foot tall row of sugarbush plants (Rhus ovata) started showing the stress of seven years of severe drought. They have not been on an irrigation system for decades, since they are native to our valley and normally receive adequate moisture from seasonal rains. But seven years of almost no rain was just too much for them. Their leaves turned brownish-black, most with tiny holes like miniature buckshot; whole limbs were dying, and leaves were becoming scarce on the limbs that were surviving. It was grim. These plants had for years formed a thick privacy screen along our property boundary. Now we could see right through the branches.

Deep-water stakes to the rescue! We bought dozens of 2-foot long, hollow plastic watering stakes with holes along the sides, and a pointed end to make installation easy with a rubber mallet or hammer. In some places, our soil was so dry and compacted, we had to soak the soil with water first to pound the stake in.

We installed a stake between each adjacent plant, and one stake on either side of each sugarbush. We were careful to place the stakes under the “dripline” of each plant, the area under the ends of the branches, where the root system is most active and absorbs moisture. The area right next to the crown of the plant, where the stem comes out of the soil, does not have roots that still absorb water; roots near the crown have barked over, providing structure but not absorption. Many plants suffer from fungal rot if the soil near the crown is continually saturated during warm weather.

These watering stakes are not cheap, but we weighed the cost of losing our trees, and watering much more frequently at the surface and possibly still losing the trees, versus the water saved by watering deeply only every few months.  We felt the expense was worth it in the long run. You can make your own deep-water sleeves by cutting short sections of PVC drainage pipe, digging holes next to your plant, burying the sleeve under the dripline of the plant, filling it with gravel, placing your irrigation line through one of the holes, and buying a PVC cap to keep dirt and animals out. However, the caps are fairly expensive, and digging the holes to bury the sleeve next to existing plants is very labor-intensive and can damage plant roots. Deep-watering sleeves made of drainage pipe are most practical if they are installed when a new plant is first planted. We also like the ease with which the manufactured stakes can be pulled out by sliding a screwdriver through the top set of holes, pulling the stake out of the ground, and pounding it back in further from the plant’s crown as the plant grows.

The cap of each stake has a small slit to allow placement of a ¼-inch irrigation line into the stake before fitting the cap over the stake. Since we don’t have irrigation to this far section of our yard, we rigged up a hose ending that fits down into the stake (plastic tubing attached with a hose adapter to a garden hose), and watered with our garden hose.

We slipped our plastic tubing into the stake, turned on the faucet to a fast drip/slow drizzle, and set a timer for 6 hours per stake. To our amazement, we started to see not just new leaves, but entire new branches growing within two weeks. We did this just once in April, and again in June. We will not water them again until August or September, if we don’t get any monsoonal rains. With ample winter rains, supplemental irrigation won’t be necessary; however, if we have just a small fraction of our normal winter precipitation, as we have had for multiple years in the past, we might try one deep-watering session over the winter. If these plants hadn’t been so stressed from years of drought, they could likely thrive with just one or two deep watering sessions per year. So many new branches have regrown on every plant that we again have a thick privacy screen shielding us from the street. We feel we rescued these beauties from possible death, or at least a fate so unsightly we would have had to cut them back severely and hope for some regrowth next winter.

We will be testing deep-water stakes on some of our other deep-rooted native plants to determine whether an occasional deep, subterranean soaking keeps them from going totally summer dormant. Like they say, we don’t want to fool Mother Nature, but we would like to give our valiant desert native plants a little boost during our new climate regime of hotter and drier days. We will report back on our results.

Until then, remember that occasional deep soakings are better for your desert-adapted plants than frequent, shallow watering. Deep watering teaches plant roots to grow down deep to find moist soils, protecting roots from drying out at the surface.

Shallow watering teaches roots to stay near the surface to find moisture, but surface soils heat up fast and dry out quickly. There is little protection for shallow roots if the surface soil heats up and dries out. Roots will never learn to go deep if trained to stay shallow—condemning both of you to a schedule of constant irrigation. For desert native plants, frequent summer watering can speed them toward root rot and death. If you can’t resist watering your struggling natives during the summer, make like a summer thunderstorm and put lots of water on them over one or two days, then let the soil dry out completely before creating another “monsoonal storm”.

As we sip wine on our Hobbit Deck at sunset, it makes us smile to look over our 1/2-acre desert garden and see native plants not just surviving this extreme summer heat, but thriving.

 

P.S. Deep-water stakes are available locally at Cactus Mart in Morongo Valley, Home Depot stores, and online from “Deep Drip Watering Stakes” at www.deepdrip.com.