Irrigation usually to blame for yellowed leaf edges

: I have a mature lemon tree with discolored leaves. The edges of the leaf have yellowed and the rest of the leaf is green. The leaves have been in this condition for years. I have had very good lemon crops every year except when the wind blows the blossoms off. I deep water once a week during the summer. The tree appears to be very healthy except for the yellowed edges of the leaves; can you help me with this problem?

Also, what type of fertilizer should I use and how often to use it is best for this climate?

A: I looked at the picture you e-mailed to me. It shows some yellowing around the edges with some scorching as well.

To me, this usually means inadequate irrigation, salt problems and/or poor soil. My first reaction is that once a week watering in the summer may not be enough. I would try to water twice a week if you can and apply a deep watering so that the water penetrates to a depth of about 18 inches in at least half of the area under the canopy of the tree.

Make sure the tree has at least two drip emitters if you are using drip (I prefer four) or that water fills a basin under the tree to a depth of about 4 inches.

Apply a fertilizer for citrus just before new growth in the spring. This is the only application you will need unless you see some specific problems such as chlorosis or yellowing of the leaves.

If the soil is bare under the tree or has rock mulch, you will see a big difference in the tree if you use a wood mulch; it should be applied to a depth of at least 4 inches.

Q: Would you please tell me the proper time and way to trim the Fan-tex ash trees? We have two that are getting a little too large for our backyard. Anything you can do to help us would be greatly appreciated.

A: When pruning ash it is good to remember that they do not grow back as vigorously after pruning as some other trees might so you want to be careful and not remove too many limbs. Remove limbs from the lower canopy only if you have to. In ash, if you do not need to prune, don’t.

If you want to lower the height of a tree, do it using a technique arborists call “drop crotching” and avoid topping. Topping is cutting the trees limbs all at the same height straight across at the desired height. This leaves tree “stubs” that, in the case of ash, will either not grow back or grow back poorly. Instead, select the tallest limbs and remove them at a crotch where they come together with a lower limb.

By removing the taller limb, it leaves behind the lower one without leaving a stub. Remove three or four of the taller limbs in this way. The remaining limbs will have leaves and buds for the growth to continue at a lower height.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.