Watering a Lawn May Not Be Enough For Trees Growing in a Lawn

Q. My tree is 30'x 25' and it is in a lawn area. We follow the SNWA guidelines for watering our lawn. Very little die back has occurred on this tree, and the only fertilizer it gets is what it steals from the lawn.

Tree dieback after the lawn was removed and rock
landscaping replaced the lawn.

A. Watering enough for a lawn is not enough for a tree planted in the lawn if you are not overwatering the lawn. Watering a lawn is enough for the lawn only if you are watering it correctly.

            When you put a large tree on it then you must deep water the tree as well as water the lawn. Different types of trees require more or less water than others. Tree water use is dictated by the size of the tree and the type of tree. Size is most critical. The only time trees do well in lawns is when the lawn is overwatered. The reason trees did well in lawns in the previous years is because lawns were overwatered.

New growth is often a different color from
the older growth

            As the price of water has gone up, people have chosen to conserve more and follow lawn watering guides more closely. This has caused some trees to be underwatered even though they are in lawns.

            Lawns are big fertilizer hogs, particularly nitrogen. If you apply fertilizer to the lawn then the lawn is what is going to get the fertilizer due to its extensive fibrous root system. Trees should be fertilized separately from the lawn with applications in the rootzone, just below the rootzone of the lawn so that the lawn does not burn.

            You can judge if the tree is growing enough by looking at its new growth this past year. It will be a different color than the older wood. Or you can see where the previous year's growth stopped. On a tree that size you should get 12 or more inches of new growth each year. If not, then something is wrong. It might be a lack of water or lack of fertilizer or both.

Modesto ash decline

            I don’t know the type of tree you have but make sure you do not have Modesto ash decline if the tree is Modesto ash. I sent to you a picture of Modesto ash decline and have posted it on my blog. It is common here but does not hit every Modesto ash. I have been working with this problem for over 25 years with other professionals and no one has been able to determine its cause. This is why I no longer recommend this particular ash tree.