By Robin Rivet.
Although April showers may offer some respite, most yard trees will soon rely solely on you for a drink. Unfortunately, that dependence often results in a spritz, not a sufficient drench. A quick douse around the trunk may make you feel better, but it does little to thoroughly irrigate tree roots.
No matter whether it’s a thirsty avocado, a moderate-drinking magnolia, or a drought-tolerant bottlebrush, recommended watering regimens suggest penetration into the soil of at least a foot, and preferably down 2-3 feet. As trees mature and their roots spread wider and deeper, frequency can be reduced. Typically, the most drought-tolerant species - often have the most far-reaching roots.
HOW TO WATER A TREE -
Big buckets with ¼” holes drilled in the bottom can water young trees easily.
Large trees need greater applications of water - but less often. A good option is installing a pressure-compensating drip system like Netafim™. This tubing can be permanently installed under a mulch of wood-chips - which also reduces evaporation. Areas where water isn’t needed can be connected to solid, poly-tubing, creating a ponytail. An example is this TRIC device as proscribed by UC Davis.
Soaker hoses are less expensive, and coiling one around a tree’s dripline while connected to a garden hose overnight - can also be effective, as long as you leave the water on so it barely bleeds, and does not run off.
If you’re hoping I’m going to tell you how often you need to water, I’m not. That will depend on your soil type, the outside temperatures, and species of tree. If your specimen is small and newly planted, it will likely need at least bi-weekly watering as the weather begins to warm up, and twice that - as it gets hot; especially when rain becomes a 4-letter word you only read about in the news.
Mature landscape trees typically get by with irrigation every 2-3 months, but deep soaking is imperative. And, if your tree once relied on lawn sprinklers, there are likely surface roots which will need gradual coaxing downwards to seek deeper percolation, so former lawn trees usually need more frequent irrigating.
COST OF WATER -
A good soaking need not break the bank either, as people tend to over-estimate the annual cost to irrigate a few shade and fruit trees in their residential yards.
If you watered a ≤4-year-old tree every week for 35 out of the 52 possible weeks in a given year, (assuming December-March are rainy), and you applied 3 five-gallon buckets at a time, that equals 535 gallons/year. You are billed in 784 gallons per unit increments by water agencies. And, if you watered SIX trees similarly, you would accrue ~4.01 units over the course of the year. One water unit costs between ~$5.00-$7.00 dollars each, so assuming a mid-range rate, watering all six trees shouldn’t cost much more than ~$24.00 all year.
And, if you think larger trees cost too much - consider this: If you install a 50-foot perimeter drip system with 1 gallon/hour emitters running overnight for eight hours, that’s 50/gal per hour or 400 gallons. Run that at least 3-5 times between May-October for a range of only ~ $9.00 to $15.00/year per tree. Surprised?
Member Robin Rivet is an ISA Certified Arborist, Consulting Horticulturist/Landscape Designer (sustainable gardens; shade & fruit trees; wildlife habitats) - contact her: firstname.lastname@example.org