THE DIRT GARDENER THANKS FOR ASKING BUZZ BERTOLERO a p r i l 2 0 1 6 A L I V E E A S T B A Y 31 I have a group of establish redwood trees planted on a slope. I thought they were being watered by a natural spring but I’ve come to find out it was from a neighbor’s leaking water line that now has been repaired. Since then four trees have died. How do I go about saving the balance? Redwoods are not a drought tolerant tree like a pine, cedar, deodar and other conifers. They're also shallow rooted and suffer from water stress with the hot afternoon sun beating on the soil. In their natural habitat, the needles catch moisture from the marine influence. The moisture then drips slowly down to cool and moisten the roots under the canopy of the trees. Hence they need to be irrigated frequently once the rainy season concludes. Stand alone trees, those with no vegetation growing under them, often struggle while those planted in a vegetative ground cover thrive. Established trees on drip irrigation suffer more than those watered by conventional sprinklers. The whole idea behind watering is to get the entire root system wet. The root system of a Redwood is found under the canopy of the tree. A common mistake made when watering Redwoods is that the volume of water is insufficient, infrequent and it’s not uniformly distributed around the tree. When using a drip system, there is a lack of understanding on how to make it work efficiently. First off, a drip system distributes water in a gallon per hour while a conventional system provides water in gallon per minute. A drip system needs to run forty-five minutes to an hour to provide the necessary volume to get the roots wet. In addition, you’ll need a dedicated water line for drip irrigation. A huge conflict develops when a drip system and conventional sprinklers share the same line. The volume of water plants receive is either too much or not enough. The second issue has to do with the number of emitters around the trees. The originally installed emitters need to be reposition every couple of years and additional emitters need to be added so water is available throughout the root zone of each tree. There is a misconception that if you puddle water in one spot, all the roots will benefit. The water absorbing roots are not located at the tree trunk but out toward the drip line of each tree. Redwoods produce a lot of natural litter or mulch to help with the moisture retention. It also insulates the roots from the hot sun, especially those trees where the lower branches have been removed. A two to three inch mulch layer under the canopy and beyond is recommended. It’s not necessary to mulch the base of the trees. In addition, your gardening service should be discouraged from removing this valuable covering. When the temperatures are over eighty degrees, I would be watering weekly. In summary, water and mulch are the keys to keeping your trees healthy. Can I be assured that the nutrients from a dry fertilizer will find its way to the roots when I water with drip irrigation or should I hand water the material into the soil? With a granular fertilizer, I'd scatter the pellets within the drip irrigation distribution pattern and then hand water it in. After that, the drip system should do the rest of the job. If you were using a time-release fertilizer such as Osmocote, it would be absolutely critical. These products only release a tiny bit of nutrients with each watering. If you’re still not sure it s getting to the roots, I suggest you switch to liquid fertilizer. Q. A. Q. A.
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