Wednesday, February 20, 2013
Weed Cloth and Red Death Kill Soil
Two things kill the soil on most of our public and commercial landscapes and many residences in Grants Pass: weed cloth and fine bark mulch, also called Red Death, often used in combination. Under the influence of water and gravity, dead soil compacts nearly as hard as rock. Roots won’t grow in it; they grow on top of it, just under the cloth, under the bark or gravel covering the cloth, or in the Red Death. Storm water, instead of percolating into such soil, runs off into streets, down storm drains, and pollutes our river.
Weed cloth (and its cheap relative, black plastic) kills soil by stopping the movement of worms and other soil life. Worms under the cloth, unable to get to food on the surface, eventually run out of food under the cloth and starve. Ants, the other great soil aerators, are not able to live under weed cloth either; nor are any other insects. With no life to lighten the soil beneath the cloth, it compacts and loses oxygen, which roots need to breathe. Any further root growth is on top of or just under the cloth, on top of the dead soil.
One might think it’s a good idea to put landscape cloth on paths under gravel or mulch, to make the soil compact and keep it that way. But roots will grow on top of or just under the cloth; this gardener recently dug and cut out a cottonwood root that had grown 8 inches high across a path of cloth covered with gravel over a mere 7 years.
Another problem with weed cloth and plastic is that mulch will not stick to it, and it soon shows along the edges and anywhere the soil is humped, by the growth of roots for instance, and where it shows, it’s ugly.
Fine bark, or Red Death, kills soil by leaching bark’s toxic natural preservatives into the soil. Trees make chemicals in their bark to protect themselves from insects, fungi, and bacteria. Grind it up, break the plant cells, and those preservatives are released to leach into soil, where they quickly kill insects, fungi, and bacteria. Dead as a doornail, the soil compacts under the influence of water, and roots begin to grow on top of the soil, in the bark.
Neither weed cloth nor Red Death kills plants directly, but some plants cannot stand compacted soil, sicken, and die. That’s why businesses have pansies and petunias planted in blocks of potting soil, surrounded by Red Death. Most common landscape shrubs in our town can take compacted soil, or they don’t last long and aren’t used by landscapers. But they grow slowly and are not healthy in dead soil.
Weeds grow regardless; gravel or fine bark are dandy seedbeds for them, even on top of weed cloth. They don’t have to be big to be ugly weeds; ugly little weeds spread just as readily and look just as ugly. Seeds are tracked in and fly in. Roots under the cloth find their way out along the edges. So it doesn’t even work to stop weeds.
Larger screened bark, shredded wood-bark mixes like Walk-on fir, and chipped wood or trimmings do not kill soil, as the preservatives are kept in the bark. It is the bark dust and small particles that leach enough preservatives to kill soil. Since larger barks keep their preservatives, they last a lot longer. The larger the bark, the longer it lasts, but walking is easiest on Walk-on and ¾” nugget, and Walk-on fir sticks well to slopes.