Many years ago, a new customer told me about her five-figure landscape overhaul plans. The “Philadelphia-area landscaper” she was hiring was going to do this and that, and he was going to put in a complete irrigation system. At that point, I was only handling mowing, fertilizing and clean-ups for this customer, but I asked her anyway, “Are you sure you want to spend that kind of money on a system you will only need to use a maximum of a few times a season?”
Five miles away, we have a customer with a complete irrigation system. They never turn it on until mid-July when the grass begins to show stress from hot and dry spells. But then, having relieved the lawn of its stress, they do not turn off the system until late September. In the meantime, even though their lawn is green, the light daily rinse provided by the irrigation system turns their clay slope into a skating rink nearly impossible to walk on.
Both of these cases illustrate two initial factors when considering purchasing an irrigation system. The factors are climate and soil type. On the one hand, most of our trees and lawns “require” an inch of water per week for optimal health. Between rain and snow, our area annually gets an average of just under one inch of water per week. Anecdotally, our climate does not require supplemental irrigation except in the “droughts” that occur occasionally in July or August, but seldom both. Even though water supply is not the only factor in keeping our lawns green, an inch of water delivered once every ten days for a few weeks in July or August will be enough to keep lawns green. For most residents, dragging out the hoses and sprinklers a few times on an as-needed basis is worth the cost savings over the installation and maintenance of permanent irrigation systems.
But why only a few nights per season? At the shore—not to mention our skating ring customer—the sprinklers go on every morning. What is the difference? The answer is soil type. At the shore, the water runs straight through the sandy soil. If the plant does not use it today, the water will not be there tomorrow. However, for soil with a higher clay and/or organic material content, the water is held in a sort of savings account: It does not dry quickly, especially further away from the surface.
For this reason, homeowners should do two things to be water- and plant-wise. First, manage your plants to encourage deep, not shallow roots. Second, if you water, water deeply to sustain and feed the deep roots. This is why the industry standard mantra is “Water infrequently. Water deeply.” Irrigation systems are most economical in sandy soils, where water is needed on a daily basis.
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Joshua Arp is an ISA-certified municipal specialist, Clarks Summit’s municipal arborist and an operator of an organic lawn and landscape maintenance business.