GARDENING: Heat brings different problems to lawns and gardens

This is the time of year that it is hot and so with the heat we have certain problems that go along with it. Let's cover a few of them.

Brown spots on lawns. The most frequent cause of brown spots is lack of water, usually because the irrigation system is not working properly or the water is not applied evenly by the irrigation system. So, most people, when they see a lawn turning brown, crank up the irrigation system. That's the usual solution since it looks like the lawn is lacking water. It's easy to do and doesn't require much time or thought.

Let's try a different approach. I would still recommend you keep the same number of minutes on your irrigation clock throughout the year. This may be anywhere from 10 to 15 minutes for popup sprinklers, split into several applications.

When changing the irrigation clock, change the number of days each week that the irrigation system starts. So, for instance, if you are watering a lawn once a week in January for 12 minutes total time, then in July or August you would be watering once a day for 12 minutes. As weather cools this fall, water every other day for 12 minutes. When it gets even cooler, water every third day and so on.

If you have water running off the lawn and into the streets, then either get that lawn out of turf, aerate it or water in increments of three or four minutes each until you get to your total.

This method of watering does not apply to drip irrigation.

Check the brown area with a long screwdriver to see if the water is penetrating evenly in the lawn. If it is not then you should check the irrigation system for even application, called uniformity, or aerate the lawn. Yes you can aerate anytime. However, dethatching should be done in September or October.

The second cause on tall fescue is the disease called summer patch, usually striking in late June or July and extending through August. As I mentioned in an earlier article, we have an information sheet for you on this disease if you call our Master Gardeners at 257-5555.

The third is insect problems like white grubs that are root feeders and kill large patches of grass and can look just like summer patch. However, recently killed grass should pull up easily from the lawn with no roots.

Recently laid sod during the heat can show brown dead spots. This is because the sod is laid on very hot soils that kill the roots of the sod in some locations, causing it to turn brown in large spots. Dry soil can be 165 degrees at midday. This can kill the roots of sod laid directly on top of it.

Leaf scorch. Plants have brown leaf margins or leaf dieback to the veins; or, in extreme cases, leaves drop or branches may die back. Basically, it is because the water that the plant needs is greater than it is getting from the soil. The plant can't get enough water for the entire leaf so the places on the leaf farthest from the water-carrying veins dries up.

Why isn't a plant getting enough water to its leaves? This could be because it just can't handle this kind of desert heat, or it could be the soil is dry, or it could be that there aren't enough roots due from diseases or insects, or it could be that the water in the soil can't reach the leaves soon enough because the trunk is damaged.

To solve these problems will require some sleuth work on your part. When a plant is not suitable for this environment or it is planted in the wrong location or both, leaf scorch is a frequent plant response. Plants that like milder climates but planted here in full sun or in places where there is a lot of reflected light or high winds will scorch during the summer.

A second reason for leaf scorch, although more rare, may be chemical damage of some sort. Plants in poor nutritional health also will scorch easily. For scorching to occur on plants that are suitable for our climate something is interrupting the uptake or transport of water to the leaves. This could be in the soil -- things like salts that need to be flushed with water, root rots because of too much water or poor drainage, or the opposite reason such as infrequent watering and dry soils, soil pests like nematodes or insect root feeders.

The problem could be in the trunk -- damage to the trunk from weed whackers or mowers, borer damage, sunscald on thin-barked trees because lower limbs were removed at pruning time, tree wraps, among others.

The problem could be on individual limbs -- cicada damage from laying eggs on limbs of trees like ash, diseases like sooty canker attacking limbs of trees like mulberry, broken limbs, heat from vehicle exhaust too close to the plant, overhead irrigation from salty water, etc.

When you see leaf scorch, ask yourself if this plant is suitable for our area and climate. Are there others just like it nearby and are they showing the same signs, or is this the only one? Is it planted in the right location? Is it getting too much sun? Is it getting too little water? Too much water? Is the water draining from the roots? Is it planted in a desert landscape and it shouldn't be? Or is it a desert plant put into a wet landscape and shouldn't be. Are there signs of mechanical damage from mowers? Weed whackers? Rabbits? Is there a lot of reflected light? Is it exposed to a high wind area? Was this recently a desert soil high in salts but recently developed and planted? Do I see evidence of pest damage?

Sap oozing can be heat related. The possible causes are heat stress, mechanical damage, damage from borers and damage from diseases. Plants don't normally leak sap unless they are damaged in some way. Very often when people see sap oozing from a tree they jump to the conclusion it is from borers. That's not always true. If it is coming from plants very susceptible to borers then it could be. Trees like the stone fruits (peach, apricot, flowering plum and plum) all have a better chance of having a borer problem than trees like ash, mulberry, elm and others. Trees susceptible to borers here are those that I mentioned and the cypresses, Hollywood twisted juniper, loquat, pyracantha, and a few others. Most trees are relatively free from borer problems.

Soil. The soils in Las Vegas present some very difficult conditions not only for gardeners, but also for our homes. Some of the cracking of walls, foundations, corrosion of aluminum or steel and collapse of soils can be attributed to the chemical nature of our desert soils. Natural chemicals in our soils, when they come in contact with water, can cause chemical reactions to occur that corrode concrete, steel and aluminum used in our buildings.

For more information on this subject and ways you can deal with it, call our Master Gardeners at 257-5555 and ask for our new fact sheet on corrosion of concrete and ways to deal with it.

Bob Morris is on vacation this week. The original version of this column appeared in the View on July 30, 2003.Plants that like milder climates but planted here in full sun or in places where there is a lot of reflected light or high winds will scorch during the summer.


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