This time of year we probably don’t think about the irrigation needs of our beloved trees. Summer will be here soon enough, so you might want to clip and save this article!
How to water your trees, then? Don’t waste your money with the silly little moisture meters that you plunge into your houseplant pots, they just aren’t suitable for the job at hand. What you need is a 36″ soil sampler probe, and you can order them from A.M. Leonard Co. (free plug).
This will set you back about 80 bucks, but it is the best way to KNOW the moisture (or lack/excess) of the soil within the root zone of your tree. This tool will enable you to extract a “plug” of soil when you push it into the ground. After pushing it down as far as possible, it captures a core sample. Withdraw the core from the probe and squeeze it in your hand. If it crumbles and blows away in the wind, it is too dry, and if you can wring water out of it like a sponge, well, you get the picture…
Take measurements from about halfway from the base of the tree to the far end of the furthermost branches, and about half that distance beyond the end of the branches. This is roughly the area that will be needing water. When you need to irrigate, soak this area for an hour or two with a sprinkler, back off for an hour, and give it another thorough soak session, and BOOM! Done!
Forget about drip systems for large mature trees, they aren’t up to the task, except for trees in pots, or small, new plantings. Your soil in the valley floor will be mostly clay, and “above the boulevard” will be granite, but no worries, the probe will eliminate the guesswork.
To retain the moisture in the soil, mulch, mulch, mulch! About 3″ should do it, and put it down BEYOND where you stop watering to cool the encompassing soils.
When some trees need water, they will let you know by wilting. Most conifers will probably croak by the time you realize you should have been watering. Probe often, and early in the growing season, and keep a record!
With the ridiculous city rates for water during the dry months, you may want to share the cost of a water truck with your neighbors for your big trees, and did I mention mulch? Mulch, there, I said it again! If you feel the need to fertilize, remember to keep the numbers on one hand, like 4-3-2, or thereabouts. Properly mulched, most trees will not need supplemental fertilizer.
In a nutshell, water infrequently and deeply, water AWAY from the trunk, water where you want roots to grow, mulch everywhere, and probe often! Riparian species will require more moisture than trees that have evolved in arid climes, but you already knew that…
Trees that are moisture stressed (too much or too little) are stressed just the same and subject to failure. If you have a tree in a lawn, and you stop watering the turf, for heaven’s sake, don’t forget to water your tree!
Casey P. Roland Tree Care