Leaf mulch: good for the flowerbed, good for the watershed
by Tim Kuhman (Associate Professor of Biological Sciences at Edgewood College and Friends of Lake Wingra board member)
Every autumn as the days get noticeably shorter with each passing day and the trees throughout my neighborhood begin to drop their leaves, I watch as frustrated homeowners tackle the Sisyphean task of raking those leaves off their yards and out of the streets. They rake and re-rake as the wind blows their neat piles around and new leaves continue to fall incessantly for weeks or months. For some, this task is all about maintaining a neatly manicured lawn. Others realize that being a good steward of our Madison lakes requires vigilant raking of leaves so they don’t end up in the storm water drains and ultimately in the lakes where they decompose and release their nutrients into the already nutrient-laden lake water, leading to an overabundance of aquatic plants and algae. Regardless of the reason, raking all those leaves is viewed by most as an obligation. I, on the other hand, see opportunity in all those falling leaves! Instead of feeling the burden of having to dispose of them, I think of the benefits and beauty they will bring to my flowerbeds the following year as leaf mulch. Turning those leaves into mulch takes little more effort than raking them into piles for the city to pick up, and keeping those leaves on your property means you won’t need to purchase mulch or fertilizer for your flowerbeds ever again. Leaf mulch is my preferred form of mulch for flowerbeds. It is easy to spread, looks nice, substantially reduces growth of weeds, and decomposes to provide valuable nutrients and organic matter that continually improves garden soil. While it was once possible to purchase leaf mulch in the Madison area, it is no longer being sold by garden centers due to the risk of spreading the recently introduced Asian jumping worms. However, by collecting the leaves from your own property and turning them into leaf mulch, you can simultaneously help protect our lakes from excess nutrient inputs and produce high-quality leaf mulch that will improve your flowerbeds and save you money.
All you really need to make your leaf mulch is a lawnmower with a removable bag and a place to pile your chopped leaves for the winter. Most mowers either come with a bag or can be outfitted with one for minimal cost. Leaves can be mowed directly off the lawn and out of the street with the mower, or they can be raked into shallow piles and then chopped by running the mower back and forth over the pile until all the leaves have been chopped into small pieces. I like to spread a medium sized tarp on the ground near where I am mowing so I can frequently empty the mower bag onto the tarp and then haul the filled tarp to the pile where the leaves will be kept until the spring. Alternatively, you can use a leaf mulcher/shredder to chop the raked leaves directly where you’ll be turning them into leaf mulch. I set up a large compost ring in my vegetable garden, selecting an area that I know I won’t be planting until a little later in the spring or early summer. I like to connect two or three of the “geobin” type compost bins together to make a larger ring that is about eight or ten feet in diameter, but the size will vary depending on how much leaf mulch you wish to make given the extent of the flowerbeds that will need to be mulched and your availability of leaves. (Though keep in mind that if you need more leaves than you have on your own property, many of your neighbors would undoubtedly be delighted to let you mow them off their yards, too!) Simple hardware cloth or chicken wire can also be used to make the leaf mulch bin. There are four main factors that will determine the speed at which your leaves will be converted to the dark-colored, partially-decomposed leaf mulch that is best to use on your flowerbeds: size of the chopped leaf fragments (the smaller the better), volume of the leaf mulch pile, wetness of the leaves, and time. There are tradeoffs between all these factors. For example, you could make a pile of coarsely chopped – or even unchopped – leaves and if you’re willing to let them sit for a full year or more before using them they will eventually turn into perfectly fine leaf mulch, or eventually compost. However, most of us don’t want to store the leaf mulch pile for more than the winter months, so faster is better. Having a larger pile helps maintain higher temperatures in the center of the pile due to the metabolic activity of the decomposers that are breaking down the leaves. These higher temperatures further speed up decomposition. The decomposers also need a relatively wet environment, so keeping the leaf pile wet is important. If there aren’t any heavy autumn rains that soak the pile before winter sets in, you should consider soaking the pile thoroughly with a hose and sprinkler. I also like to collect a few of the large brown paper leaf bags that some neighbors place on the curb, and I set them on top of the chopped leaves to help weigh them down and hold in moisture after soaked them with water. The unchopped leaves in these bags don’t turn into very good leaf mulch for the flowerbeds, but they work great to mulch the aisles of our vegetable garden in the spring. I even cut the paper bags into strips in the spring to place under the leaves in our veggie garden aisles as an extra weed barrier. It can also be helpful (and fun!) to have kids jump on the leaves in the pile to pack them down so more can fit in the bin and so they stay wet longer after they are soaked with water.
Instead of begrudgingly raking your leaves to the curb this fall, consider getting your mower and leaf mulch bin ready now so when the leaves start to fall, you will be ready to enthusiastically collect those leaves and turn them into leaf mulch, with visions of beautifully mulched bloom-filled flowerbeds in your head. You will have the satisfaction of knowing that you’ve done your part to protect our Madison lakes, save some money, and beautify your property at the same time. Happy mulching!