The Pre-historic War: Trees vs. Grass

Have you ever noticed that grass does not grow well in the shaded areas of your yard?

Have you ever planted a young tree in the middle of your lawn and noticed that it just doesn't seem to thrive like the same trees you planted in a planter bed outside the grassy areas?

Sadly, I went to the Annenberg Space for Photography and saw a horrible battle taking place in the wonderfully expensive and beautifully MAN-ipulated landscape. If you have the chance, the Annenberg Space for Photography is an incredible and mind blowing museum for the display of photography. It will truly change your life. Afterward take a trip outside to the beautifully landscaped battle, just outside and down the steps.

The landscape designer for this beautiful complex tried to create a garden space that was very emotionally pleasing. He succeeded for the most part, however, at the moment several of the trees are being held up with ugly cables. Why did this happen? The designer failed to realize that tree roots grow more slowly when they are planted in grass. No roots = no support = falling trees.

Grass and trees are both capable of producing allelopathic chemicals and both have evolved to safeguard the light and soil resources closest to them.

Both trees and grass have evolved to be capable of chemical warfare. Allelopathic chemicals are chemicals produced by plants to inhibit the growth of other plants near them. Some plants are better at it than others and there are different ways these chemicals enter the soil. Most commonly they leach into the soil from decaying plant material such as leaves fallen from a tree or grass cuttings.

Grass has evolved to grow very dense and tightly together. Rain, and even modern fertilizers rarely make it past their thick mat of green leaves and roots. This soft, lush mat of green grass is what we love most about having it in our yard. The trade off however, is that trees, our shade providing friends, obtain their water and nutrients only after they pass through the layer of grass.

Trees have evolved to grow very tall to shade the soil, providing water conservation and soil temperature stability. In the forest, a thick layer of decaying leaves covers the ground. Grass has a difficult time getting the sunlight it needs to produce photosynthesis and allelopathic chemicals inhibit the grass from establishing.

The plant that has been established the longest in the area you are troubleshooting or landscaping is going to always have dominance over the other plants. A large tree will make it very difficult to grow grass and an established lawn will make it difficult to grow a tree. It is a fact of nature. Limited resources cause wars for survival.

In conclusion, try to separate tree root zones from grass/turf and vice-versa. I always recommend mulching 12 inches away from the base of the tree, all the way to the ends of the drip zone beneath trees. (drip zone is the area under a tree where rain will drip from the leaves onto the ground.) Never cover the base of the tree with decaying material. The mulch should be mixed into the soil and spread in a 3-4 inch layer. Trees planted in grass will produce 1/3 the number of roots as a tree planted in mulch.

P.S. Don't forget keeping the root crown at the base of a tree dry and free from wounds is important for tree health. No Mower Wounds and No Weed Wacker Wounds!