We have left our lawn go brown, and now the leaves on our forty-year-old Fruitless Mulberry are dropping. We don't water it much as the shallow roots grow in the lawn area. Do you think the canopy has outgrown its root system?
. No, I do not think your Mulberry has outgrown its root system as they're not a short-lived tree.
This is a drought-related problem. In previous years, frequent lawn watering was sufficient to support a mature tree. However, dry winters, water restrictions, and several triple-digit heat spells show their effect on mature landscape trees throughout the area.
While you may have stopped watering your lawn, you should not abandon watering mature trees. They more than pay their way with the energy savings, the cooling effect from the shade, and the increased property value.
Trees with exposed roots and or shallow-rooted varieties such as Redwoods are susceptible to water stress. It's not too late to take some positive steps this fall and to continue them next year and beyond
. Mature trees should be watered every three to four weeks, June through October, depending on the temperatures. This is particularly important for those areas replanted or not planted at all.
I'd mulch the exposed root area with a three-inch layer of organic matter to replace the insulation effect from the previous lawn. You could use bark, compost, other plants' natural debris, and shredded household paper. Also, be sure not to bury the crown or base of the tree with the mulch.
Next, under the canopy, set up a drip system or, better yet, use my favorite soaker hose, the grandfather of the drip irrigation system. Soaker hoses offer a slow and steady release of water to your tree(s). The slow release allows the soil around tree roots to absorb the water gradually. And the proximity of the hose to soil means that very little, if any is lost to evaporation. It's tough to know how long you should run your soaker hose to get enough, but not too much, water into the ground.
You should apply six to eight inches of water per month in one or several waterings. The easiest way to calculate this is with a shallow container such as a tuna can. It's placed under a section of hose, and you see how long it takes it to fill up with one inch of water. You then multiply that by six or eight to determine how long to run your hose.
Once that's determined, you automate the process with a Dramm Water Timer attached to your hose bib. With turf being replaced with water-wise planting, mature trees will suffer unless measures are taken to replace the moisture the previous lawn provided.
NOTE: Here are two short videos produced by the Forest Service and California ReLeaf on how to water mature and young trees. They are worth viewing - https://youtu.be/lrirPBMTYi0 and https://youtu.be/P_kQZriJ38U.