Beaumont-Wilshire: The Real Dirt
(Editor’s note: Eileen is a BW resident, landscape designer, and author of Real Gardens Grow Natives: Design, Plant, and Enjoy a Healthy Northwest Garden*.)*
It’s so delightful when we see butterflies or bumble bees in our yards, but they’ll never reach their beautiful adult phase if we rake or blow away leaves from bare soil. Many beneficial invertebrates—such as most butterflies and moths, syrphid (flower) flies, spiders, and ladybird beetles (ladybugs)—wait out the winter in a dormant state as larva or pupa (or even egg or adult) in decaying plant material and emerge in the spring to carry on their species. Queen bumblebees take cover under fallen leaves as young adults and emerge from their sleep when warming spring temperatures signal it’s time for them to begin their new colony. Many other native creatures rely on leaf litter as well, and it’s a great way to attract our feathered friends. Worms and insects nesting and overwintering under debris provide natural food for hungry birds, especially ground feeders like thrushes and sparrows who need leaf litter in which to locate dinner. In springtime, fast growing baby birds benefit, since almost all are fed high-protein insects and spiders, not seeds or fruit. Rain and dew on fallen leaves also provide essential moisture for many species.
This fall, sweep or rake fallen leaves from storm drains, walks, driveways, and other hardscape, but leave the leaves as well as other organic material—such as stems, twigs, and bark—on soil, as nature intended. Besides providing shelter, food, and nesting material for wildlife, leaf litter and woody debris keep plants healthy by insulating them, suppressing weeds, maintaining moisture, and feeding and protecting the soil, which can degrade fairly quickly from excessive rain, wind, and sunlight. The leafy organic layer eventually breaks down and becomes a rich humus with the help of invertebrates, bacteria, and fungi that specialize in moving carbon into soil, storing it there, extracting nutrients for plants, and protecting them from disease. Mowing over small amounts of leaves on lawns will gently increase their fertility, unlike synthetic fertilizers that kill soil organisms. You can let the city pick up any additional leaves at curbside, but to benefit your garden even more, consider using them to make compost. Leaf compost is considered by many to be the best ingredient for any soil, because it improves soil structure and increases moisture retention; it can even be used to replace nonrenewable peat in potting mixes. Simply place leaves in a round chicken-wire cage in a shady spot. Keep the pile moist (but not wet), and you will have leaf compost in one to two years. Also, keep some extra leaves to add to regular compost, which should be roughly half “greens” and half “browns.” When applying compost as mulch, remember to leave some soil bare for beneficial, non-aggressive native ground nesting bees, and keep it a few inches away from tree trunks and stems to prevent rot.
Thus, the leaf litter layer is a mini-ecosystem rich in life. Leaving the leaves saves time and money, helps sustain wildlife, and enriches the soil by allowing nature’s cycle to return nutrients to the soil.