By Janice Gestner, Master Gardener
There are several options for mulch or soil covering in our gardens. Choices can be either organic, which are compostable materials that improve soil fertility, or inorganic film coverings that can be black, red, green or silver colored. Inorganic film mulches are often sold in rolls. Mulch can improve our plants and gardens in the following ways:
- Moisture retention/water conservation
- Soil temperature control and stabilization
- Weed suppression – weed growth is eliminated when light is not available
- Soil borne disease prevention
- Improved soil fertility through decomposition of organic mulches left on the top of the soil
- Minimize soil erosion and compaction from heavy rains and help with water absorption
- Improved landscape appearance with clean and neat mulch between plants
In the spring, gardeners have to decide what type(s) of mulches to use. The best mulch application time is after the plants are established, four to six inches tall, and the soil has warmed up enough for active root growth. Mulch applied too soon will delay root development. Be sure not to touch the plants with the mulch. Many plants such as tomatoes are planted only after the soil is sufficiently warm. For tomatoes and other warm season transplanted plants, it is best to apply the mulch immediately to avoid soil splash-up/soil borne diseases. If you are using an inorganic film, you can add a couple of layers of newspapers under the film to help with weed suppression. The newspaper is a safe, compostable layer.
Depth for most organic mulches is two to three inches to provide the positive results described above without becoming too heavy. Mulch applied too deep can cause a lack of oxygen to roots, can yellow foliage, and could provide a space for small burrowing animals to feed on plant stems. In fact, be sure that the mulch is close but not touching the stems!
Favorite organic mulches include straw with newspaper under it to prevent light to seeds, compost with newspaper under it, brown decomposing paper rolls, dried grass clippings, and mulched leaves. Other possible organic mulches include cocoa bean hulls, pine needles, and crushed corn cobs. Gardeners who choose to use straw should be sure to buy tight bales that do not have too many seeds. Some gardeners have also successfully used burlap bags, and they can be reused year after year. Mulched leaves may need to be reconsidered this year and in the near future due to jumping worm concerns.
Jumping worms are a type of angleworm, but they change the soil texture to make it look like coffee grounds. As they move and eat, they strip the soil of nutrients and kill plants. They are recognizable, in part, by their whipping action. They live in leaf litter on the top floor of forests and hatch in the soil in late spring. All gardeners in Dakota County need be aware of them and on the lookout for them. For more detailed information about them, please read the University of Minnesota article titled “Jumping Worms”. Another excellent article is “Coping with Jumping Worms” by Karen Randall. The damage jumping worms can do should cause gardeners to reconsider the types of mulches that they add to their gardens. At this time, there are no known ways to easily rid the soil of jumping worms once they are present.
Inorganic mulches may be considered as alternatives to organic mulches. They do not break down and add nutrient value to the soils, but they help with several of the mulch attributes described above. Black, red, green and silver plastics provide weed control, splash-up protection, and some temperature control. Red plastic used with tomatoes is said to improve crop harvest by 20% because it reflects growth-enhancing light waves from the sun. It can be used with newspaper under it to control weeds and help conserve water. The down side of inorganic mulches, in addition to initial cost, is that they add to environmental plastics and may or may not be reused in a future year. Inorganic mulches can be found either in garden centers or in seed catalogs.
Mulch can be a great addition to your flower or vegetable garden. However, take care in choosing a type that will benefit your garden.