Mulching beds have become extremely popular now, and mulch can be really beneficial to your plants and the soil in your planting beds, but there are things you need to watch for.
The most popular type of mulch that people use is shredded hardwood bark mulch, a byproduct of the timber industry. When they haul the logs into the sawmill the first thing they do is debark them. The bark was a huge problem for the mills years ago, because there didn’t seem to be a useful purpose for it until people realized the hidden benefits that it held. Still, to this day, the bark is a headache for the sawmills, they don’t always understand how to properly handle it.
They like to pile it as high as they can so it takes up less space in their yard. There is little demand during the winter months. This can become a huge problem for you or I if we happen to get some mulch that has been stacked too high, and compacted too tightly.
When the trees are first debarked the mulch is fairly fresh, and needs to decompose before we dare use it around our plants. The decomposition process requires air flow and oxygen into the pile. This air flow cannot take place when the mulch is compacted too tight, and the mulch continues to decompose it becomes extremely hot as the organic matter ferments. Sometimes the extreme heat combined with the inability to release the heat can cause the pile to burst into flame through spontaneous combustion.
When the mulch heats up, cannot release the gas, and the mulch actually becomes toxic. The mulch develops an overbearing odor that will take your breath away as you dig into the pile. When you spread this toxic mulch around your plants the gas it contains is released, and this gas can and will burn your plants.
The gas, not the mulch, turned the grass brown next to the mulch pile. Some people spread several yards of the mulch around their house before they realized the problem, and it ruined many of their plants.
Here’s the hard part, trying to explain to you how to identify toxic mulch. It has a very strong odor that will take your breath away. But then again almost all mulch has a powerful odor.
The mulch looks perfectly normal, maybe a little darker in color than usual. If you suspect a problem with the mulch you have, take a couple of shovels full, and place it around an inexpensive plant. Maybe just a couple of flowers. When doing this test use mulch from inside the mulch pile and not from the edges. The mulch on the edge of the pile has more than likely released most of the toxic gas that it may have held. If after 24 hours the test plants are okay, the mulch should be fine.