Weeds Can Be Introduced on Straw Mulch

Written by: Fred Yelverton and Leon Warren

Straw from small grain crops is often used on new seedings of fescue and other cool- season grasses. The  advantages of using straw are:

  1. it holds moisture near the soil surface which can result in greater germination and survivability of seeded cool-season turf
  2. it can help prevent soil washing in the event of a heavy rain event.

Straw bale used as mulch

Even though there are advantages of using straw for this purpose, there are also disadvantages. Straw that is  available for this use is usually wheat, oats, or field rye. Combines that harvest these small grains do not remove
100% of the seed. When the straw is spread on the newly seeded area, the small grains germinate and grow  along with the cool-season turfgrass species. These small grains then become serious weeds of the cool-season  turf. Where there are high densities of small grains, the cool-season turf can be shaded out and competition from  the small grains can result in poor establishment of the desirable turfgrass species. Under low densities,
turfgrass establishment will be fine but the small grains can be unsightly and are essentially weeds that cannot  be selectively removed from the cool-season turfgrass species. Fortunately, these small grains will die out in
late spring or early summer and so long as the area is mowed and the small grains do not produce seed, they  will not be a problem in subsequent years.

Another common problem with straw is that various weed seeds can be introduced with the straw. Small grains  such as wheat, oats, and rye have their own weed problems and if the weeds are present when the crop is
harvested, the straw will contain weeds. One of the most common weeds of small grains is annual ryegrass  (Lolium multiflorum). Annual ryegrass can be a serious competitor of newly seeded cool-season turf. Other  common weeds include chickweed, henbit, wild radish, wild garlic, and hairy bittercress. Annual ryegrass seedhead found in straw bale What can be done to prevent this problem? There are alternatives to using straw as mulch. Polywoven covers  can be used that allow water and light penetration and help keep the soil from drying out. The disadvantage is  these covers tend to be expensive. The other alternative is to use nothing. If this approach is taken, timers can be  used so that water can be applied 3 to 4 times/day to keep the soil moist. Watering cycles should not be long  and should last just long enough to keep the soil moist on top. Usually 15 to 20 minutes on a particular head is  adequate. Timers can be purchased at lawn and garden stores. The prices range from about $15 to $50. The  higher priced ones work the best because they can be programmed to apply up to 4 cycles/day. There is also an  option to skip days if necessary.

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