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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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May 12

The Root of the Problem

Posted on May 12, 2017 at 11:12 AM by Ann Vallee

by Charlene Burgi

Lawns are thirsty. In fact, they are the highest water-using plant in a garden. There are thousands upon thousands of grass blades that comprise a small lawn. Those monocots need to be supported by a lot of water and fertilizer to maintain that lush green color we are all partial to sinking our bare feet into. But did you ever wonder what makes lawns so thirsty?

roots
 Grass roots vs. large-leaf weed roots
To be honest, I hadn’t given this question a lot of thought. Of course, I’ve always known this high-water-using vegetation is not well suited for our dry summers, which is why lawns are best considered for small, frequently used patches. Oddly, it was while I was weeding that a light went off that gave me a better understanding of why lawns use so much water. 

Weeds are growing at an incredible rate thanks to all the rainfall we’ve received. Fortunately, the damp soil makes weed-pulling a breeze. With that chore literally at hand, I tugged at a clump of grass. It wasn't a very large clump, but as I pulled on it the supporting root system came loose. The width of the root system was staggering, far surpassing the area of the grass found above. Millions of tiny roots clinging to bits of soil exposed the real issue of why lawns need so much water.

For fun, I pulled up a large-leaf weed to compare its root system to that of the grass. A single thick waxy root told the rest of the story. That single root has the capacity to store large amounts of water to support the large green leaves for long periods of drought, compared to the very shallow, tiny, hair-like roots of grass. There is very little storage capacity in lawn roots, which makes them very dependent upon the condition of the soil where the lawn is growing. If you maintain a patch of grass, four inches of good loamy topsoil will help hold onto moisture and support your lawn with less irrigation. A well-designed and installed irrigation system providing head-to-head coverage is a must, too. 

Creeping thyme
Creeping thyme
Lawns are beautiful and take a lot of abuse. But they are high-maintenance, subject to insect and fungus problems, and have an understory that requires volumes of water and fertilizer. For me, I think I will continue growing patches of creeping thyme and Turkish speedwell. They are low-maintenance, thrive in the heat with minimal water, and can even take some foot traffic.

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