Editor’s Note: In Botanical Rambles’ previous two autumns, we’ve looked at Washington’s most colorful fall leaves and at the fall color of berries and beach plants. This year, Jamie Bails invites us to take another look at the value of fall leaves.
A few years ago, after watching my neighbor rake and bag fallen cherry leaves, I asked him if I could save him a trip to the dump. He hesitatingly agreed, and I quickly loaded up eight lawn bags into my wheelbarrow before he changed his mind. I giddily spread the leaves as mulch around my perennial beds.
In my neighbor’s world, leaves should be raked and bagged, bark mulch spread, and shrubs pruned into pleasant shapes. That’s not my idea of gardening.
The next year, they cut down the cherry trees, but they saved me a wheelbarrow of leaves. For now, a nearby 100-year-old big leaf maple (Acer macrophyllum) and the native trees I’ve planted provide a healthy supply of leaves as mulch.
It’s unfortunate that more people do not see the value in fallen leaves. that leaves extract 50-80 percent of the nutrients and minerals from the soil. Transporting this bounty to a landfill or paying curbside recycling to take it away doesn’t make much sense if we want to make good use of natural resources.
Benefits of Leaf Mulching
- Regulates the temperature of the soil, keeping it cooler in summer and warmer in winter.
- Reduces weeds, as long as the mulch is weed free and deep enough to prevent weed germination or smother existing weeds.
- Prevents the surface of the soil from cracking or eroding.
- Prevents rain water from running off the soil and disappearing down a storm water drain.
- Prevents water from splashing up onto plants, which slows the spread of soil-borne diseases.
- Prevents the soil from crusting or compacting.
- Increases and strengthens root growth.
- Creates a natural forest floor environment.
- Provides food for earthworms which in turn improve the health of the soil.
- Improves and adds nutrients to the soil.
Leaf litter and soil erosion
Leaf litter is the dominant pathway for nutrients to return to the soil, especially for nitrogen (N) and phosphorus (P). The accumulation of these nutrients in the top layer of soil is known as soil immobilization.
Once a leaf has settled, its decomposition is helped along by several forces:
- Rainfall leaches out the nutrients into the soil
- Bacteria, fungi, and other microorganisms digest and decay the leaf
- Critters like insects, millipedes, and others (known generally as detritivores because they feed on detritus) that eat and recycle the leaf.
Without a covering of leaf litter on the soil, rain will release the clay and silt particles. These particles enter our waterways, increasing the amount of sediment carried out to sea—not good for many reasons. Such soil also can’t absorb as much water, which speeds up soil erosion.
Leaf litter also reduces wind erosion by preventing soil from losing moisture and being blown away.
Many different species of decomposer fungi are found in nature, especially in the soil. They are usually most active when temperatures are warm and the environment is moist. As a vital part of the decomposition process, these fungi help enrich the soil by making nutrients available to in a form plants can use.
A wide range of creatures take part in the decomposition process. Most of them are relatively inconspicuous, unglamorous, and, from a conventional human perspective, even undesirable.
This detritivore community includes beetles and their larvae, flies and maggots (the larvae of flies), woodlice, fungi, slime molds, bacteria, slugs and snails, millipedes, springtails and earthworms.
This community works mostly out of sight, and the work happens gradually over months or years. Cumulatively they are the unsung heroes who convert all dead plant and animal material into forms that are useable for growth either by themselves or other organisms.
After the glorious fall-colored leaves drop to the ground, here are several ways you can utilize the leaf surplus instead of sending it to the landfill.
Leaf Compost Methods
Slow-Compost Method: Rake the leaves off the lawn (assuming you still have lawn) and pile them on your planting beds. This will make the rich humus and leaf mold similar to that in a forest.
The leaf nutrients will quickly leach out while the remainder of the dried leaf will slowly compost over the winter, putting nutrients directly back into the soil with the aid of the detritivores.
This is a great method for soils that are clay, compacted or very dry. It’s also a good method for gardeners without access to manure, as the slow-decay will not smother or burn plants.
Lawn-mower method: Run your lawnmower over the leaves and rake them onto planting beds at about a 2 to 6 inch thickness. When spreading the leaves, be careful not to cover the crowns of your plants.
This is a great alternative to purchasing several yards of beauty bark or wood chips.
This method shreds large leaves like those of big leaf maple (Acer macrophyllum) and helps them break down more quickly. Large, leathery, evergreen leaves like those of madrona (Arbutus menziesii), or cherry laurel (Prunus laurocerasus) also benefit from this type of shredding, or they can take several years to decompose.
Compost Pile Method: Store leaves in feed sacks, and over time you can use them as brown material for your compost pile. Another approach is to corral an abundance of leaves in a wire cage for decomposition over the winter. By spring, the compost can be spread on beds.
Livestock Method: If you keep poultry or livestock, use your supply of leaves for litter or bedding along with straw or hay. Leaf mold thus enriched with the manure’s extra nitrogen may later be mixed directly with soil, spread throughout the garden, or added to the compost pile.
The Slow-Compost Method and the Lawn-Mower Method are both excellent ways to encourage beneficial insects in your yard. Insects such as beetles, spiders, and centipedes readily crawl under leaves for protection through the winter, as well as deposit eggs in the soil or leaf litter.
One final note: if you don’t have enough leaves, ask a neighbor if you can rake their leaves for them. Gather them onto your yard or use a tarp to collect and distribute them. You neighbors may think you are crazy, but you’ll be walking away with valuable free soil amendments.