Let’s pay homage to humus. As the garden 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 (not to be confused with the tasty dip hummus) 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 that join small clay particles into larger aggregates. Large aggregates have large air spaces between them, and 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 exactly right. And humus binds with certain nutrients to make them more easily absorbed by plants.
Physically, the sponginess of humus makes soils fluffier even as it absorbs water.
Humus is one of the few things in life your soil can’t get too much of. Although it’s naturally present in all soils, you have to conscientiously preserve and augment it if you garden.