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Sunday, November 3, 2013

Dethatch Bermudagrass Just Before Overseeding or in Mid-Summer

Q. Is it too cold to dethatch my Bermudagrass lawn?  Do I have to wait until next year now? What about overseeding; too late also? If I need to wait, then when?

A. It is not too late to dethatch in Las Vegas. Dethatching, sometimes called power raking or vertical mowing, is the removal of dead, grassy material that accumulates on the soil surface where grasses are grown.
Dethatching machine, power rake or vertical mower
            Bermudagrass is a warm season grass and so becomes dormant or turns brown when temperatures get cold. Bermudagrass produces a lot of this thatch or dead grassy material, more than most grasses. If this thatch is not removed regularly the appearance of a lawn will decline.
            Years ago it was burned in the fall. In some rural areas it is still permitted.
            In place of fire we use machines that pull the thatch from the lawn. This thatchy material is then disposed of. The best time to dethatch is when the Bermudagrass is actively growing in the summer months or just before overseeding.
            Overseeding is planting a new lawn of cool season grass, such as ryegrass, in the fall just as Bermudagrass is becoming dormant. Thatch will interfere with the seeding of a winter lawn in Bermudagrass. Dethatching the Bermudagrass just before overseeding is commonly done for a better looking winter lawn.
            Dethatching now won't affect your Bermuda lawn but you are getting a bit late for the ideal time to overseed. As temperatures get lower, it takes longer for cool season grass seed to germinate. The ideal time is mid-September through mid-October. Later than this can be a little chancy because we don't know what the weather will do.
How thatch accumulates
            It is warmer in the city than in the suburbs so overseeding in the city is more successful later in the fall. As you get closer to the desert or higher in elevation overseeding should be done earlier.
            If you miss this time for dethatching, the next best time would be June July and August.

Trees Planted in Grass Need Extra Water

Q. I had a 3 year old mesquite tree in my front yard that just blew over in the wind today.The original landscapers planted a tree without a drip system. I have an area of grass around the tree and they told me in the past that that is sufficient to water a tree. Today the landscapers that came to cut down the tree told me it fell because of the roots being at the surface. Do you recommend putting in the drip line? I can tell you the soil under the tree was very moist from the sprinklers. I have attached a picture of the felled tree. Any suggestions for a tree that would be sturdy to the wind? The original tree planted was a glossy privet that died after the first year. It was replaced by the mesquite. I have to plant something in the 24 inch box size per HOA rules.

Mesquite tree that blew over
A. I am sorry to hear about your tree that blew over. This can be a problem sometimes with trees that are planted in or near lawns and rely only on lawn irrigation. Lawns require shallow irrigation that are frequent. Trees and large shrubs require a larger amount of water applied less often. Be very careful of planting trees that originate from deserts and used for desert landscaping (examples are acacia and palo verde) planted in the lawn. This usually does not work well. Trees that are suited for lawn areas are those that are not desert trees.

Trees and large shrubs getting water only from the lawn will fight for the shallow irrigations of the lawn. If you are an efficient lawn irrigator, the tree will have a difficult time getting the deep irrigations it needs for deep rooting. When trees are planted in large turfgrass areas, such as golf courses or parks, the trees always grow faster and perform better if they are supplemented with water for the first few years. After three or four years of successful growth, you could eliminate the hose irrigations around the trees except perhaps during the hottest parts of the summer.

Mesquite roots can good deep if given a chance. This is a native mesquite in Zacatecas, Mexico, near a river. The roots had found moisture from the river but not at the surface and so were forced to go deep where moist soil was located.
Some golf course superintendents would send out a water truck once every week or two to flood the area around the tree with water. This encouraged deeper rooting and kept the lawn from robbing the tree of its shallow water supply.

You can do the same thing with a hose. When a tree is planted in the lawn area it is best to leave a shallow depression around the tree 3 to 4 feet in diameter. This can be a basin for flooding the area around the tree every week or two with a hose. It also helps, as you have done, to keep that area free of grass and weeds. If you can remember to water with a hose, particularly during the heat of the summer, you can save yourself the expense of installing a new drip line.

Mesquite trees are what we call riparian tree species. Unlike Palo Verde or acacia in the desert, Mesquites are only found near waterways. They grow when water is available and stop growing when water is not. When water is constantly available, they constantly grow. When Mesquites get water they can grow quite rapidly, as much as 8 feet in a single year. 

Honey mesquite with mistletoe in the Mojave Desert in North Las Vegas
This is a problem when they receive constant watering because their tops grow faster than their roots and this contributes to blow over. For this reason Mesquites are not a good choice for a lawn area but are more appropriate for a desert landscape. In lawn areas stay away from desert trees. Trees like many ash, Locust, honey locust, privets, and others are not desert trees and they will survive in the lawn much better.

Personally, I think you are better off without the lawn unless you have a use for it. You can substitute green groundcovers and achieve a similar look to a lawn. When you plant trees and you do not have a lawn make sure that you surround the trees with some smaller shrubs to help keep the trees irrigated. Focus on smaller trees that are in scale to your home. Don't put in 40 foot trees if you have a single story home. 

Take advantage of the shade they give and put them so they shade the south and west walls and provide shade to where you have outside activities. Trees should probably not be planted just for looks in the desert. They should also have something to contribute to your comfort as well. So remember to keep your trees small, use desert adapted trees whenever possible, minimize the use of tall trees and shrubs to reduce your water use and to make sure they contribute to your home environment and your outside living environment.

Fig Limbs Hollow and Not Because of Borers

Q. I have a fig tree that is close to 30 years old. It was getting out of control so I have been pruning it. I noticed some holes in the trunk but as I am cutting the branches I find that some are completely hollow inside.  Other than a few dead areas that I am pruning out, the tree looks generally ok and is putting out new growth, even from the hollow branches. Since the main trunk seems to be involved I can’t really cut out all the part that is affected.  Can you tell me what is causing this and if there is anything that I need, or can do about it???  I noticed the hollow where I had cut out a branch from the trunk a long time ago, but did not worry about it.    I would like to save the tree, it has sentimental value and provides needed shade.   I have attached some photos.  
Readers fig tree with hole in the trunk

A. Your pictures through me for a loop a bit. I have not seen that on fig before but I have seen something similar on other trees. I knew it was not from borers but I was not sure why you lost the center of your fig trees.
            When trees grow, they grow both upward and in girth. We know that upward growth is from the buds on trees. Growth in girth is not as obvious. Growth in girth is from some cylindrical layers just under the bark.
            As a fig tree gets fatter, the center of the tree dies. As it continues to grow fatter and fatter, the dead wood in the center of the tree gets larger and larger. As long as the tree remains healthy and doesn't get any infections, the deadwood in the center of the tree remains intact.
            On some occasions, organisms such as fungi and bacteria can invade the center of a tree and begin feeding on this dead wood. These organisms are almost always feeding only on deadwood and not the living parts of the tree.
Fig limb hollow
            So these organisms technically are not disease organisms but wood-rotting organisms. Since the center of a tree is dead, these organisms continue to feed on this dead center of the tree and can hollow out a tree very effectively. I think we have all seen pictures or cartoons of animals living inside of trees. Well, this can actually happen.
               The center of the larger trunk and branches of a fig tree are filled with dead wood that is fairly soft and pithy. Once these wood-rotting organisms get going they will clean out that central core of large branches and the trunk. The living portion of the tree is unaffected.
               What you have is not a borer problem but a wood rotting process going on. There is nothing you need to do about it but keep in mind that these branches may snap more easily than branches which do not have the central core hollowed out.
            This is one of the reasons I emphasize so strongly to clean your pruning saws and pruning shears before you start pruning. It is best to clean and sanitize them between each tree, not necessarily between each cut unless you know the limb is diseased.

Tree Selection for Mesquite Nevada

Q. Can you suggest some trees that could be planted in the Mesquite, Nevada, area?

A. I am not trying to avoid your question about a recommended tree. However I do not like to recommend trees to homeowners because the selection of trees is not purely logical, it can be emotional as well. I do not know what trees you like or do not like and I do not know what is available to you.
Trees out of scale with the house. They shade the roof okay but we really want to shade the west and south facing walls where the insulation is not as thick and has a lower R value.
            Because trees can require a lot of water, tree selection can also have a huge impact on our natural resources. If you can come up with four or five trees that you like I can help you from that point.
            Try to base your selection on the size, whether you want deciduous or evergreen and whether it should flower. The size of the tree should be in scale with your house. If your house is single-story, it should be no more than 20 to 30 feet tall when it is mature.
            Big trees use more water than little trees. If your water bill concerns you or might concern you in the future, use smaller trees and use fewer trees. Trees in the desert should shade South and West facing walls or windows on those walls when possible.
            Woody plants are deceiving in their water use. They don't use much at first when they are small but when they get bigger their water use goes up proportionately. Just what that proportion is depends on the type of tree it is. There is no clear cut answer for that.
            If they are being used for shade it is best to select deciduous trees, trees that lose their leaves in the fall. If the trees are going into desert landscaping, it would be best to select desert trees. If the tree is going into a lawn area or an area that we consider to be high water use such as a sitting or patio area than you do not need to use desert trees. Make sure your trees are hardy in Mesquite to at least the mid teens in the winter. I hope this helps.