News from the MMWG!

We are advised to “leave the leaves” on the ground in the fall. What should we do with them in the spring?

Many Marin gardeners allow fallen autumn leaves to remain on the ground throughout the winter. During that time, the leaves gradually decompose, forming mulch that retains moisture in the soil and provides nutrients for plants. Importantly, leaf litter also offers shelter for ground-nesting bees, moths, beetles, lacewings, and other beneficial insects. And allowing leaf litter to decompose naturally helps rebuild soil health.

But what about when spring arrives? As spring flowers emerge in your garden, you may feel tempted to create a cleaner look by removing the remaining leaf litter, possibly replacing it with purchased mulch.

The dilemma: While the purchased mulch may look tidy and will benefit the plants, it comes at the expense of the insects hidden among the decomposing leaves.

Here are three general options to consider:

1. If you decide to remove leaf litter, wait until the weather is relatively warm (i.e., daytime temperatures above 55-60 degrees). In Marin, this is usually in late March to mid April inland, and somewhat later along the coast. By this time fewer insects will need this habitat. You might also consider getting a yard sign from the Xerces Society that explains your reason for keeping the leaves.

2. If you really do not like the look of leaf litter, consider adding a thin layer of purchased mulch over it. This will likely preserve some of the insect habitat while affording a more uniform backdrop for your plants. And the new mulch will also contribute to soil health.

3. Try a variety of approaches in your yard. For instance, you might consider leaving leaf litter under trees and shrubs, or in a fenced-in area that is somewhat more out of the way. But you might add a layer of mulch to the leaf litter in publicly visible areas, or in those where the plants are young and small, thereby leaving the leaf litter more exposed and visible.

   Remember that even a small part of your yard can be a valuable insect refuge if covered with leaf litter that is allowed to remain relatively undisturbed year round.

Note: Monarch butterflies are not part of this picture — they are overwintering in tall trees along the coast and have no need of a leaf-litter habitat!

To some gardeners, the small plants in this winter garden may seem overwhelmed by the abundant leaf litter and magnolia petals. To others, it is a pleasing palette that will continue to improve as the growing plants take up more space (photos: Susan Holloway)