Thursday, March 24, 2011

Adding a composting trench to the garden

After reading about incorporating vermicomposting into a garden by creating a worm compost trench, I decided to give it a shot in our makeshift greenhouse / garden box. We have already added a fair amount of amendments to the soil, but after our poor results last year, I wanted to make sure that the plants would continue to have a good supply of nutrients throughout the growing season. Essentially what you do is to dig a fairly deep trench near a row of vegetables. The plants can be just starting but shouldn't be far enough along that the trench would impact the roots. Then you just fill the trench with layers of food scraps, manure, straw, shredded newspaper, or other compostable items in a reasonable balance so that the resulting compost will provide a good source of nitrogen. (Be careful of too much carbon, such as leaves, straw, wood chips, and paper) The idea is that the compost will eventually break down with the help of the worms and provide nutrients to the nearby plants which will actually grow their roots towards the rich compost. When I first started gardening years ago, I tried some of the time released chemical fertilizers but I think that this natural organic method will be even superior. (fingers crossed!)

Is it me, or something about this idea seem odd to you? Everything that I have read and my own experience has shown that uncomposted organic material can actually be harmful when added directly to the soil where your garden plants are growing. The key to this technique is to create the composting trench far enough away from the young, tender roots, are not damaged by high composting temperatures or by loss of nitrogen during carbon fixation but close enough so that when the compost starts breaking down and building up new sources of nitrogen, it becomes immediately available to those roots when they are mature enough to reach out and use them.

I went ahead and dug the trench down the middle of the entire length of the box in the "greenhouse". I dug down about six inches to the clay soil under the garden box and piled it up on either side. Another unplanned benefit with this technique is that both long rows have about a foot of good soil before the roots hit the hard, clay soil underneath. I had saved about five gallons worth of vegetable clippings, which I chopped into small bits to speed the composting, which went to the bottom of this trench. I added about a wheel barrow load of uncomposted rabbit manure mixed with hay to cover the chopped veggies. I'm pretty nervous about adding this "hot" manure, but since I won't be adding worms for a while and it will take a while for the seeds we planted on the rows next to the trench to even germinate, I'm hoping that things will even out. Maybe the hot composting action of this trench will even help to warm the soil and the greenhouse. Obviously there is a lot that I have to learn about balancing the nutrients that seeds need to germinate and grow, but I think that this sounds promising.

Actually, the idea to use the rabbit manure in the garden came from another gardening blog from "El" in Michigan. She has chickens, goats, and rabbits and builds hot beds in the Spring to get a jump start on warming the soil enough for the seeds to germinate. The difference between us is that the composting trench makes it so that I'm not planting directly over the compost like the hot bed technique. Hopefully mine is a reasonable compromise of the two ideas.

But wait... will I still get a benefit if I just do the composting trench without adding composting worms too? Well for one thing, composting worms are not going to like the compost if the composting temperatures make it too hot. It takes time anyway before the worms would be happy in that trench. Without the worms, it will just take longer for the compost to break all the way down. With the worms, they will be able to work through the compost and make those nutrients more readily available to the nearby plants. Either way, I won't have to dig the compost out of a compost bin or worm bin and add it to the plants. It will already be close enough to be useful.

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