We 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 using leaves in the garden. 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.
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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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3 Responses to “Things We’ve Learned: Leaves”
Just pulled a ton of weeds out of my garden, put them in to compost, will seeds decompose or will I just have another record crop of weeds?
I have used hay in the past to mulch with, and then turning garden does this deplete nitrogen?
Gardeners in Northern California know that madrone leaves make a good mulch that makes garden plants grow well. Madrones shed leaves in the summer. I rake up madrone leaves, mowed grass, twigs, fir cones and needles, etc, from my yard during the summer. I spread it on my garden in mud-winter. After a couple of months in the rain the leaves are soft and partly decayed, and there are always lots of earthworms beneath them in the top layer of soil. I put organic chicken manure on top of the leaf mulch (about 1/2 lb per square foot) , and spade it all fairly deeply into the soil. It seems to work for me. I usually surface dress, lightly, with chicken manure in mid-summer. I have been doing this for about seven or eight years in my current garden. I have close to neutral soil acidity.
Possibly the only problem I have with such loose and mulchy soil is that the sowbug population is pretty high, and those little beasts just love to eat the skin off stems of bean plants.