Friday, September 25th, 2009...12:00 am

Why Grass Might be Difficult to Grow

Oak Alley by Lake Fred

Oak Alley by Lake Fred

TheGardenLady received this question on a post about acidic soil from Todd.

My yard had many oak trees in it. I have stopped letting leaves sit so I can start a decent yard.  Could this be the reason grass is so difficult to grow?

If you want grass to grow on a lawn, it is good that you stop letting leaves sit on the grass. Grass loves sun. Even the so called shade grass doesn’t like a blanket of leaves covering because all grass needs light. And grass is a heavy feeder. Some kinds of grass need more fertilizer than others.

Grass really doesn’t like to have competition from tree roots.

You wrote that your yard HAD many oak trees in it. What does that mean? Did you chop the trees down? If you still have oak trees in your yard, know that oak trees are also heavy feeders. Their roots want the nutrients and the water to feed the trees. Tree roots are like pancakes- spread out. 90% of tree roots are in the top 3 feet of soil and 50-75% of feeder roots are in the top 1 foot of soil.

Roots may actually grow 2 or 3 times beyond the drip line (the edge of foliage) and near the surface. So if you have one oak tree the root is spread out at least as wide as the width of the top of the tree. The more trees you have, the more your yard is filled with roots. The more roots you have in your yard, the less grass you can grow. They don’t want to share. Grass is difficult to grow under the oak trees because the grass and the roots of the trees are competing for the nutrients and water.

Some people say that they can get grass to grow under one oak tree. They recommend that you add about 2 or 3 inches of compost or good potting soil to the area where you want the seed to grow. But do not add too much soil because that will be bad for the roots of the trees. Get a good perennial grass seed that grows well in the shade in your area and put it down thickly. Now you will have to do a lot of watering. Especially in the late spring and early fall when the weather is still warm, you should water for 2 to 3 hours a couple of times a week. And remember that you will have to fertilize the grass as recommended by the manufacturers of fertilizers, in the spring and fall.

But since you write that you have many oak trees on your lawn, even though a green lawn is a thing of beauty, are you sure that you want to do all the work that it requires to make a beautiful lawn? Even with the desire, because of the economy and the change in the environment, more and more people are recommending not having anything as work intensive or water needy as a lawn. If there is a drought, as there was this summer in the southwest, people are often told not to water their lawns. Without water the lawn will probably die and if the drought is bad, the oak tree may die. Finally if you don’t plant grass, you won’t have to even rake the leaves when they fall around the trees. The fallen leaves make a good, healthy mulch for the tree.

Consider a lawn alternative. There are plants that will grow under oak trees including many native plants. You can put spring bulbs under the trees. Hostas might grow well under oak trees. Azaleas should grow well under oaks. Hostas are tolerant of soil types and azaleas love acid soil. TheGardenLady recommends that when you plant shrubs under the oak tree, you do it under the drip line of the tree away from the trunk of the tree. Also, you want to avoid injuring oak bark and roots or changing the soil conditions around the tree when you plant. Remember there will be competition for water from the tree roots and the shrub or perennial plant roots so that you might need to water well until the shrubs or plants get established or if there is a drought. A good list of plants that grow under oaks in California is this or if you live in Texas check out this.

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