Learn basics of working with garden mulch
Q : Spring is coming soon, and I need to replace the mulch in my flower beds. I have noticed during winter that there is no mulch left in large areas of the beds. I am sure weeds are ready to fill in if I don’t add more mulch. The last mulch I used was from the local arborist. It didn’t last very long. Is there a better choice that would last longer or be cheaper to replace?
A : Organic mulches come from a variety of sources, and they aren’t supposed to last too long. In woodland areas, dead leaves and sticks litter the forest floor and slowly decay. This creates a nice fluffy soil that holds water, stops erosion, has plenty of air for the roots, insulates the soil from temperature extremes and helps stop weed seeds from sprouting. Grassland areas have much less organic matter on the soil surface, and in many cases, the regular occurrence of fires removes the accumulating organic matter.
If your flower bed plants originally came from forests, then around 4 inches of mulch will help them. But if they are grassland plants, only apply about 2 inches of mulch. Mulch that is too thick will block the airflow into the soil, preventing the roots from getting enough oxygen. Thin layers replaced more often are better than thick layers.
The larger the mulch pieces, the longer they will last. Bark chunks will last longer than shredded bark or arborist chippings. A 4-inch thick layer should last two growing seasons.
The decay of the organic matter is beneficial to the plants and helps create a better soil in the flower bed.
Local natural sources of bark and chips will be less expensive than materials shipped in from other parts of the country. Recycled wood from pallets or construction materials can be fine, but investigate the source if possible, so you know that the wood isn’t contaminated with paint or chemicals.
Dyed shredded wood is becoming more common. It may be fine if the source wood was good. And some of these products include chemical weed control products that last an entire growing season.
Generally, grass clippings need to dry out before being used as mulch.
Clippings that include grass seeds some time during the season shouldn’t be used. In the fall, tree leaves make great mulch, especially if they are shredded.
Both of these materials decay within the growing season.
Gravel or recycled rubber chunks will last a long time if installed properly. They help prevent weeds and help control soil moisture, but they don’t provide any other benefit for the soil. Larger gravel will stay in place in low areas that flood, but all mulch will wash away in strong currents.
Every time it rains, the gravel will sink slightly into the mud below and eventually disappear. Installing a weed-barrier cloth below the gravel mulch will prevent the stones from sinking and help prevent weeds from coming up from the soil. As organic matter accumulates between the stones or rubber chunks, it will form a thin soil that will allow weeds to sprout.
They will be easy to remove in the shallow soil. The weed-barrier cloth prevents perennials from spreading and filling in the flower bed.
You can use the weedbarrier cloth by itself for temporary plantings, such as a vegetable garden, but the material will last longer if covered in a thin layer of mulch during the growing season. Never use plastic sheets, as they block airflow and water flow into the soil.
Never pile mulch on the trunks of trees or shrubs, for it can hide rodents that eat tree bark or hold too much water against the trunk, causing the bark to rot. Don’t bury the crowns of perennials and ornamental grass plants with mulch.