They seemed to be fine after our week of 117F weather. Q. Four years ago we planted two Raywood ash trees in our back yard. They have been very healthy and have grown wonderfully to over 25-30 feet. One is growing in the grass and the other in decorative rock. We usually water about 30 gallons every 2-1/2 week in the summer. Both trees are planted in a wide circular of dirt and mulch, about 25 feet apart. There are no other plants near these trees, so they are not susceptible to any weed killer or fertilizer that should not be used near the trees. They seemed to be fine after our week of 117F weather.             Two weeks ago one began to lose leaves. Now the other one is doing the same thing. We gave them a little extra water because the leaves are beginning to dry and feel like crepe paper and turning yellowish. We checked the limbs and bark and there doesn’t seem to be any seepage, cuts or insect damage. A. My first reaction is the trees are not getting enough water. When leaves begin to drop over the entire tree it usually points to a problem with the trunk or roots. Since water affects the entire tree, the amount of water applied is also looked at closely.             Thirty gallons every 2 1/2 weeks is not enough for trees 25 to 30 feet tall. So they must be getting water from somewhere else besides your deep watering. It is good to water trees infrequently but every two weeks is quite extreme for trees that have no other source of water.             I would normally give 30 gallons of water three times a week when temperatures are in the 110F range. Once the temperature drops back around 100F I would drop it to twice a week.             As long as this amount of water is spread in a 3 to 4 foot diameter basin under the tree or distributed by multiple drip emitters under the canopy it should wet the soil deep enough, about two feet down.             You might consider is that the extra water the trees were getting might have “dried up” for some reason. When this happens, the leaves on the tree would scorch, dry up, turn crispy, and drop. This leaves the roots to rely on other sources of water to support its size.             When tree roots find water, their roots expand into a wet area. In areas where very little water is present, tree roots grow poorly. Tree roots can spread, if water is present, distances of two to three times their height. So your 25 foot Raywood ash could have roots as far as 75 feet from the trunk.             Tree roots do not necessarily grow symmetrically around the trunk. The greatest abundance of roots is in wet areas of your landscape or your neighbors. Also, if your neighbor had a pretty wet landscape, the roots could be over there. If that is the case, how your neighbor waters, or doesn’t water, could affect your trees.             I would construct a basin or depression under your trees about four to five feet in diameter and deep enough to hold about 30 to 40 gallons. I would fill this basin with water once a week for the next several weeks.             Leaves that are crunchy will not grow back. They will dry and fall from the tree. You will have to wait for a new flush of leaves if water is the problem. This might take a couple of weeks.             To supplement the tree you can plant under the canopy of the tree (not in the lawn) with other plants that require watering. This will help to supplement that trees water requirement.             The tree in the lawn is puzzling. This would make you think there is another problem but if things happen to BOTH trees it usually points to a management problem; water, fertilizer, pesticides, etc.             When one tree is affected it usually points to outside factors that are more hit and miss like diseases. However, ash is not affected by that many diseases and is a good tree for Las Vegas.