Things We’ve Learned: Leaves

Autumn LeavesWe think of gardening as a never-ending learning process. Just when something makes sense, we learn something new — or remember some detail we’d forgotten — and suddenly, Doh!… we feel like Homer Simpson. Such is the case with composting leaves. We used to have so many. We’d heap up our compost piles and spread them over our garden. One not-so-bright day in November we decided that if we turned them into the soil they wouldn’t blow around as much. And, come spring, they’d decompose faster into the soil, enriching it with mineral-rich humus. Win-win!

No, lose. Even though we knew that carbon-rich materials use up nitrogen as they break down, we didn’t put it together with our garden soil, which of course we wanted to be nitrogen-rich. By turning those leaves into the soil, we were guaranteeing that we’d be losing some nitrogen for next growing season. Same thing happens with other carbon-rich materials: wood chips, sawdust, pine needles; even shredded paper and cardboard if you’re using it. Turning them directly into the soil will deplete nitrogen.

Of course, there’s a simple solution. Put those leaves into your compost heap with enough “green” (nitrogen-rich) materials to finish the resulting product. You don’t need much. Experts tell us that 25 to 30 parts carbon to 1 part nitrogen will do the trick If you don’t have enough nitrogen, the composting process comes to a halt. If you have too much nitrogen… plug your nose! Remember: compost is a soil amendment. It’s not a fertilizer. You’re making it to add rich, organic humus loaded with beneficial microbes (and some nutrients) for your soil, not to increase nitrogen content. (That’s what alfalfa pellets, soy meal, manures and all the others are for).

Another good solution is to make leaf mold. Put all your leaves into the traditional, three-sided box made of wood or chicken wire (you want plenty of air to circulate) and water thoroughly. Shredding the leaves first or running over them a few times with a mower speeds the process. But making leaf mold doesn’t happen overnight and your bins may take two seasons or more to become the kind of well-decomposed material that won’t sap nitrogen when its turned into your garden. It also makes a wonderful mulch.

And just for the record. When I foolishly began turning whole leaves into my garden soil, I found it a difficult process. Many still blew over into the neighbors lawn. And when I went to work the soil in the spring, I had to deal with slimy clumps that continued to rob my soil of nitrogen as they decomposed. Live and learn!

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