Puttering In The Potager – Week 6 of 2010
(Week 6 isFeb 8th to the 14th)
Mulch has critical function in the ‘soil food web’
Homestyle columnist Nancy Szerlag gets eight or more gardening magazines each month, and both of us get many newly published gardening books from publishers hoping we will give them a review in our columns. That’s a fair amount of information piling up on our desks. The question is whether there is really anything new offered in all that paper. The answer is usually yes, but you have to plow through a bunch of old information to find the kernels of new data.
One problem that surfaces and is sometimes serious is that there is not always agreement among the garden writing world concerning the need and use of compost, humus and organic material. We still find confusion among published works that often leads to bad advice. Yardeners don’t have to get down to the little gritty scientific details in this issue, but making sure you are not using bad advice is a good thing.
In the 1990s, soil scientists, discovered the “soil food web,” which I’ve discussed many times over the years. The function of all the different denizens of the soil from the earthworms down to the beneficial microbes had not been clearly understood, especially the fact that all those billions of critters make up a connected network; what one bacteria does affects what happens to another microbe next door.
When we began to truly understand the “soil food web,” we began to really appreciate the critical function of what we all call “mulch” or organic materials of some kind that we layer over the surface of the soil where we are growing plants.
We believed mulch was primarily valuable because it kept down weeds, kept the water stored in the soil from evaporating as quickly, and cooled the soil in the summer. What we now know is the most important role of mulch is to provide food for the critters making up the “soil food web.” That mulch disappears. It is pulled down into the soil and eaten sometimes many times as the soil food web creates from that organic material food for the plants, disease prevention and a general environment in which a plant can thrive. After that organic matter has been munched, the black residue is called “humus.” This humus is not food but it does important things. It is able to store lots of water for later use by the plants. It has chemicals in it that help plants maintain a comfortable pH in their root system. Humus does good stuff.
Humus is essentially the same as compost. Both are the residue of the decomposition of organic material. The big question, therefore, is if we use lots of organic material on our property in the form of mulch, does that mean we no longer need to use compost? The answer is yes and no. Compost can be a very helpful soil additive but it is not fertilizer; it does not feed the soil food web. Next week I offer new views on using compost.