Give Leaf Mold a Go

Skip the Yard Bag and Give Leaf Mold a Go—It’s Worth the Effort!

Many City of Boulder residents are befuddled by the change in curbside compost guidelines that went into effect April 1st. In particular, people wonder how to get rid of large quantities of leaves as they clean up their yards this spring. Large kraft paper bags are no longer allowed, except during seasonal collection events announced by your local hauler or municipality, per EcoCycle’s Composting Guide for Boulder County. (Customers of Western Disposal can continue to use large brown kraft yard bags placed OUTSIDE their compost bins; the organic material haulers will act as “bag concierges” and dump the contents of the bags at their transfer station, according to Western Disposal’s Special Bulletin on the Important Compost Changes) Large “compostable” plastic bags are also no longer allowed, however, smaller, 3-gallon or smaller, CMA certified bags listed by A1 Organics may be used for food scraps.

With change comes the opportunity to rethink. Let’s take five minutes to consider two ideas that may reduce or eliminate your need for yard bags: using some fallen leaves to mulch landscape plants, and using the rest to create leaf mold. (If you live near Open Space, check out important fire considerations at the end of this piece!)

Photo Credit: Leave the Leaves | Xerces Society

Using Fallen Leaves as Mulch

The Xerces Society, a non-profit organization dedicated to conservation of invertebrates like our native bees and butterflies, advises residents to “‘leave the leaves.” Many, many beneficial insects overwinter in leaves. They suggest that you rake (not blow, not mow) as many leaves as you can into garden beds and around the bases of trees. A fluffy layer of 6” of leaves will break down into less than an inch of decomposing leaves. You may have done this last fall, and our wind likely rearranged your work. Put those leaves (more decomposed now!) back into those spots now. Warmer temperatures and spring precipitation will break the leaves down quickly, plants will grow through the leaves, and the decomposing leaves will help hold the moisture in the soil and feed your trees and plants.

What is Leaf Mold?

If you have space and leaves left over after you have raked them into garden beds and tree bases, consider making leaf mold with your remaining leaves. Leaf mold is essentially composted leaves, and it comes from slow, mainly fungal composting which yields a soil conditioner with amazing properties and which is difficult or impossible to find to purchase. (cite) Most of our Boulder County soils, particularly in developed areas like homes and businesses, are very low in organic matter. More organic matter in soil allows it to soak up and hold a lot more water, moderates temperatures, holds onto nutrients and releases them as plants need them, and improves plant health. (finegardening.com and phys.org - I encourage you to do a little investigation on your own beyond my sources–all these claims sound extraordinary, but they’re backed by evidence.)

Photo Credit: How to Make and Use Leaf Mold | The Spruce

How to Make Leaf Mold

It’s not hard to “process” large amounts of leaves in town in a way that isn’t unsightly. To combat wind and our dry climate, gather your leaves in one place, contain them, and keep them moist–about as damp as a wrung out sponge or dishrag. I have had great success with this by simply making a chicken wire hoop, loading it with leaves, dampening the leaves (slow/very low sprinkler or hose for 15 minutes), and then topping with a flattened cardboard box or two (cover as much of the surface of the leaves as possible to help keep in moisture and leaves), and finishing with a few bricks or large rocks. The dimensions of the hoop can vary, but it should be at least 3’ tall and 3’ across. (A container 5’ high and 6-7’ in diameter should hold the equivalent of 25 plastic garbage bags of leaves or 35 kraft bags of leaves.) I’ve done hoops of various sizes over the years using chicken wire from the Resource Yard, but you may also be able to find it via Freecycle or Craigslist (also look at a hardware or farm supply store). Any flexible wire mesh fencing material can be used. When it snows or rains, I uncover my leaves so they can soak up the moisture. I check their moisture level periodically through winter, and on warm sunny winter days when I water my trees, I water my leaf mold, too. Just like regular compost, the leaves should be about as damp as a wrung-out dishrag. While some will advise you to run over your leaves with a lawnmower, think again. This will kill overwintering insects and cocoons in the leaves. (They are fine with moisture, but not blades.) Also, conventional two-stroke gas lawn mowers and leaf blowers emit incredible amounts of air pollution. Your pile will shrink in height as the months pass, and you should be able to harvest some leaf mold from the bottom of the pile in six to twelve months, though it may take as long as two years. (Don’t get impatient–the final product is worth it.) Check out these sites for pictures, videos, and suggestions–just remember to skip the shredding.

Harvesting Your Leaf Mold

To harvest finished leaf mold, pull the hoop off and set it up next to the pile. Throw leaves which are not yet decomposed back in (mostly leaves from the edges and top). Top this with a fresh layer of that season’s fallen leaves. The finished product should be very black and crumbly. If it’s not to this point–if there are still chunks of recognizable leaves–it needs more time and likely more moisture. However, it can still be used as a high quality top dressing, mulch, or soil amendment, with all of the benefits described above.

Important Fire Considerations

If you are within a quarter mile of open space or are considered moderate or higher risk on the Colorado Forest Risk Assessment Map, remember the Boulder Fire Department’s guidelines: clear out dead vegetation within 10’ of structures, and consider sending your leaves offsite through the curbside compost program. If in doubt, check out the tools available through the Boulder Fire Department or complete a Wildfire Home Assessment Request Form to get a free evaluation of what you can do to lessen your fire risk. In general, in these areas, to be as fire safe as possible, make sure any compost is contained and moist and more than 30’ from any structure.