Above-ground roots indicate watering problem

Q: I have two ash trees in my front yard. The roots are coming up above the ground and most anything else I try to grow does not do well. Is there any correlation between the ash trees and the problems I am having growing other shrubs, grass and plants?

A: Ash trees do relatively well in this climate and there are lots of them in town being grown successfully so it has to go back to something you are doing or not doing. I would guess this also relates to your other landscape plants.

I think a primary problem, most likely, is how you are watering. Ash trees are not known for their surface roots like, let's say, mulberry is. The presence of surface roots on trees that are not known for having surface roots is usually tied to frequent, shallow watering. In other words you may not be giving the plants deep watering or you may be watering too often.

Watering too often does not necessarily mean overwatering. You can water daily and still not give a plant enough water. Watering plants has two considerations and this is reflected in your irrigation timer; how many minutes you are watering and how many days per week water is applied.

Trees and shrubs require deep but infrequent waterings. Lawns, vegetable gardens and annual flowers require frequent but short irrigations. Larger plants like your ash trees, as they grow in the landscape, require water in much larger amounts than shrubs which do not grow as tall.

So, for instance, ash trees may have been installed with four drip emitters at the time they were planted while surrounding shrubs only required two. Let's say the shrubs and ash trees were put on the same watering station so they were watered all at the same time. The ash trees' requirement for water increases as they get bigger, year after year, much more rapidly than the shrubs. So more drip emitters must be added to the trees so that they get more water.

The shrubs, if they are larger shrubs, may also require more emitters but not as many as larger trees like the ash. Bottom line, I think you may need to water less often but with a greater volume of water at each watering.

Q: Last September my gardeners thatched my Bermuda grass backyard and part of my front yard, which is fescue. They overseeded the Bermuda grass with ryegrass for winter color. The rye did not come in very well. I think there was not enough seed that landed on the soil. The yard is still very spongelike when you walk on it even though it was dethatched. I don't know if it should be thatched again, rolled or scalped with my reel-type mower. Also, can Bermuda grass seed be used if it's scalped or just to fill in areas? I now have another problem. I believe that since the rye never took hold my backyard is covered with weeds.

A: You are probably right, not enough seed came in contact with the soil and never took root. The seed probably got hung up in the thatch. That is probably due to a thick layer of thatch.

If thatch is too deep (you can feel that by that spongy feel when you walk on it), the roots of the germinating ryegrass will grow into the thatch or the seed will not germinate at all. If the Bermuda grass is real thick with thatch, when you dethatch a lot of the lawn will come up with the thatch leaving open areas of bare soil. This can open up the lawn to an invasion of weeds.

You will not have this problem if you are dethatching regularly, which is normally done each year when you are overseeding the lawn for winter color. If you see a lot of living grass coming up with the thatch, then you will need to fill in the empty spots quickly to reduce weed problems. You should never scalp a lawn unless perhaps you are overseeding for winter color or just getting ready to dethatch.

Mowing short or close is different from scalping. If this is hybrid Bermuda grass, you should never seed a Bermuda grass into it. If the open area is very large, you can plug the open area with 4-inch-by-4-inch plugs taken from a good part of the yard that you then replant into the bare area. This keep the grass all the same type.

Bermuda grass regenerates a lawn that has been dethatched from the remaining plants . It will fill in where there are openings in the lawn and sunlight. Of course these are the same spots favored by weeds. You speed it up by fertilizing with a high-nitrogen fertilizer such as ammonium sulfate, 21-0-0. Keep it moist and mow frequently.

Mowing frequently encourages horizontal growth and discourages vertical or upright growth. Bermuda grass is a warm-season grass so it will not fill in quickly unless it is very warm or hot. So dethatching Bermuda grass should be done in the summer, not the fall or spring like you would with fescue, unless you are overseeding.

When your landscapers come in to do work, have them do the fescue first then the Bermuda grass to reduce contamination of the fescue by the Bermuda grass. Fescue seldom needs dethatching.

You will probably need to dethatch the Bermuda grass once a year -- or maybe twice -- until you get the thatch layer down to no more than one-half-inch deep. Again, do this when it starts to get into warm or hot summer temperatures.

Aerating also will help drive roots deeper and slowly get the thatch under control. Aerating can be done any time of year but is usually best just in the spring and fall for fescue and summer for Bermuda grass. You should follow aerating with a high-phosphorus fertilizer, such as 16-20-0 or something similar.

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.