Hello,

Calamagrostis x acutiflora ‘Karl Foerster’ is an ornamental grass that grows 3-5 feet tall with a spread of 1 ½ - 2 ½ feet. It grows in well-controlled clumps and is a hybrid with sterile seed heads. Read more about it here: https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b810

Grasses have shallow root systems and are easily removed mechanically. In your case, it would seem that the roots are growing above the landscape cloth, because it is the nature of the plant to increase in width to its maximum point. Therefore, it is growing above the landscape cloth to increase its size. The landscape cloth is inhibiting the natural inclination of the plant. The only way that you can control it is by mechanically removing the side sprouts. Because it is sterile, it does not spread by seed so it does not matter when it is cut down—fall or spring.

Here are some facts about the use of landscape cloth.

Landscape cloth: Although landscape cloth discourages weeds; is long lasting and allows some water to reach plant roots, there are many reasons not to use it. It prevents natural nutrients to reach the soil; restricts the movement of soil organisms such as earthworms and insects which are constantly moving through soil, mixing in organic matter and other nutrients; it compacts the soil over time and so stops air and water from reaching plant roots which then grow through the cloth and break it down allowing light in for weeds to grow in.

Mulch: Mulch provides several services in your garden. It prevents weeds from germinating; cools the soil and retains moisture; natural organisms like insects and earthworms break down the mulch and provide valuable organic matter and nutrients to be mixed with the soil. Shredded hardwood, straw, grass clippings, shredded leaves all provide this. The benefit of river rock is that it never breaks down and needs to be replaced, it does nothing to nourish the soil.

If your aim is to prevent weeds from growing in the bed, you will discover that weed seeds germinate quite well in landscape cloth where soil and sand has blown in between the rocks. Pulling those weeds is a tedious job and hard on gardening gloves. If you apply herbicide, unsightly dead plants lie on top of the rocks. Also, river rock is almost impossible to dispose of should you ever decide to have it removed.

A more organic method of preventing weed growth under mulch is to apply paper—either 3-4 sheets of newsprint or ripped up layers of yard waste bags—damp it down with water and apply a couple of inches of mulch (not river rock) on top. The paper will break down over time (it seems worms read newspapers) and prevent the weed seeds from germinating.

here are pros and cons about using landscape cloth.

Thank you for contacting Ask Extension.