Let’s pay homage to humus. As the garden season gets into full swing, it’s a good time for such tribute, because enthusiasm can be parlayed into action.
No one can say exactly what humus (pronounced HUE-mus) is because it’s a witch’s brew of thousands of organic compounds that result from the decomposition of dead plants and animals.
“Yuck,” you say? Don’t. Think of compost, leaf mold, the spongy, dark layer of earth you see when you push aside leaves on the forest floor.
Think of the rich, dark soils of our Midwestern plains, the Argentine pampas, the Russian steppes. Such soils have been the breadbaskets of the world because they are rich in humus.
Both the chemistry and the feel of humus make it such great stuff.
For instance, humus is covered with negative charges, which keep positively charged plant foods, such as potassium and calcium, from washing out of the soil.
A soil rich in humus is also rich in microbial glues. At first, glue of any kind might seem like a bad thing for soil, but what these glues do is to join small clay particles into larger aggregates. Large aggregates have large air spaces between them, and — lo and behold — formerly tight clay soil is now breathing as easily as well-aerated sand.
Humus also has buffering acidity, which means that you no longer have to be so careful about getting soil acidity (pH) exactly right. And humus binds with certain nutrients — iron, for example — to make them more easily absorbed by plants.
Physically, the sponginess of humus makes soils fluffier even as it absorbs water — just what plants like.
Humus is one of those few things in life that your soil cannot get too much of. Although it’s naturally present in all soils, if you garden you have to conscientiously preserve and augment humus.
This is because many garden activities hasten humus decomposition. Not that humus decomposition is all bad; many of humus’ benefits, such as release of plant nutrients, come about as humus decomposes. But when humus loss outstrips its accumulation, it’s like taking money out of a bank faster than you put it in.
Tilling the soil and using concentrated nitrogen fertilizers accelerate humus decomposition. Tillage charges the soil with air, causing microbial populations to soar, and these hungry microbes then gobble up humus very quickly.
Following an initial burst of nutrients, the soil is left poorer. Concentrated nitrogen fertilizers have a similar effect, so go easy on both tillage and concentrated fertilizers.
You can and should add humus to your soil. Grow it in place by setting aside part of your garden or part of the season to cover crops, which are plants grown specifically for soil improvement. Grassy plants, such as oats, rye, sorghum and wheat, are best for increasing soil humus.
And haul humus or the makings of humus into your garden in the form of compost, straw, leaves, wood chips and other bulky plant materials. Just lay these materials on top of the ground and the goodness will naturally work its way down.
You’ll also get mulch’s benefits, which include locking moisture in the soil, preventing wide swings in soil temperatures and snuffing out weeds.
Once you have gained reverence for this material, explore ways to preserve and augment it. Humus is what put the “organic” in organic gardening, and a humus-y soil is the earmark of any good gardener.
Talk to us
> Give us your news tips.
> Send us a letter to the editor.
> More Herald contact information.
