Most readers know that I consider applying mulch one of the most important garden tasks — it protects plants and enriches the soil. One of the aspects that I have not written about is how mulch helps preserve and protect beneficial insects.
All bugs and spiders and various creepy crawlies and wee beasties are going to be referred to in this article as “arthropods.” Arthropod means “jointed segments” which all of our insects, spiders, worms and many of our other soil dwelling organisms have. We know that 95% of arthropods are beneficials that provide support for healthy garden flowers and vegetables. We are probably most familiar with those insects that pollinate plants such as bees, butterflies, moths and even some flies and beetles.
There are also a host of “beneficial” insects that can attack the egg, larval, pupa and adult stages. In the spring and early summer, the “bad bugs” seem to get a head start munching garden plants. The beneficials eventually catch up and start doing their job.
One of the reason for the slow start for beneficials is that our gardening practice destroys the good guys overwintering environments.
When we totally denude the garden of all spent vegetation, exposing only bare ground (sure, it looks nice with the new snow on it), we destroy the protection that the dead leaves and stalks provide. Insects overwinter in the top few inches of the soil, and bare soil freezes more readily. Those brown seed pods, dead flower stalks and rolled up leaves harbor many insect eggs, larva and adult insects. The plant parts lying on the ground are protected from truly hard freezes since the moist soil gives off some residual heat. In addition, the snow covering the plant debris also provides a warmer environment for the insects.
There is a plus side besides just providing insectary sanctuaries. If you wait until spring to remove the garden debris, the work is about two-thirds easier because the leaves and stalks and stems, break down during the winter. So there is less material to compost or add to the green can. Even better, the decaying organic material is incorporated into the soil during late winter.
When the soil temperature reaches 40 degrees, insects begin moving about. Worms work all winter and move closer to the surface when the soil warms. The worms break down the organic material lying on the soil and carry it into the top few inches of the garden.
This year’s colorful leaves have finally fallen. I am always torn about what to do with this treasure. Do I grind them with the lawn mower and store them to use as brown material for the summer’s compost pile, or do I use them as insulating mulch on the flowerbeds and around the veggies in my winter garden. I just don’t have enough leaves!
The flower beds every year get about 8 inches of leaves. In the spring, I can see the places where the worms have incorporated the organic material into the top few inches of the garden bed. This means that the soil will retain water more effectively, and more air can get down to the plants’ roots.
Since our last few winters have been much milder than in the past, I have found that 10 inches of leaf and grass clipping mulch is effective at protecting the roots of tender perennials such as Black and Blue Salvia ( Salvia guaranitica).
I use 10 inches of leaves to mulch the carrots and beets that I harvest all winter. This amount of mulch prevents the soil from freezing and ruining the vegetables. I mark the rows with tall poles and add piles of snow if we get enough. Then those wonderful January evenings, going out into the snow and the garden to harvest frost sweet vegetable. When I dig down through the mulch, the sweet summer soil scent makes me yearn for May.
A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Bonnie Orr is one of four columnists featured.