By Darbie Granberry
University of Georgia

Compost is a hot topic. If you’ve been reading the latest
gardening articles or watching your favorite TV gardening guru,
you’ve probably seen its use enthusiastically touted.

Most gardeners agree that compost is good for the garden. But why
is it good? And how should it be applied?

Compost is what’s left of organic matter after microbes have
thoroughly decomposed it. Simply put, it’s decayed organic matter.

Through the composting process, plant and animal materials are
broken down into smaller particles. The final product has an
organic-matter content around 35 percent to 45 percent and
resembles potting media.

Organic fertilizer

Because it’s high in organic matter and doesn’t contain
“synthetic” chemical fertilizers, compost is a good source of
organic fertilizer.

Generally speaking, organic fertilizers come from plants or
animals that took up these nutrients, or fertilizer elements, and
chemically bound them in their tissues and by-products.

Because they’re integrated into complex organic molecules, the
plant nutrients in organic fertilizers are in relatively low
concentrations. They’re not water soluble. And they’re not
readily available. They have to be broken down by organisms in
the soil before the bound nutrients are released for plant roots
to take up.

This keeps the nutrients from being washed out of the soil by
heavy rains. It results in its slow release over many weeks or
even months.

Nutrient content

The nutrient content of compost varies with the materials
composted and the specific composting process. Generally, though,
it falls within these ranges: nitrogen, 1 percent to 2 percent;
phosphorus, 0.2 percent to 1 percent; potassium, 0.5 percent to
1.5 percent; and calcium, 0.05 percent to 2 percent.

Besides these major nutrients, compost also contains small
amounts of micronutrients such as boron, copper, manganese and
zinc.

Remember, organic fertilizer is slowly released. So, it usually
works best as a supplement to conventional fertilizer, not as a
replacement.

Compost, though, does more for the garden than just provide
organic fertilizer. It also helps:

• Increase the soil’s capacity to hold water and nutrients.
• Reduce soil compaction, allowing more air and water to move
  among soil particles.
• Improve the soil’s tilth, or structure, making it easier for
  roots to grow and thrive there.

How much, when to apply

Eight to 10 weeks before you plant, broadcast compost over the
garden. Any amount is helpful. But for best results, initially
apply 20 to 30 pounds of compost per 100 square feet of garden
soil. Scatter it uniformly over all of the garden.

And immediately after you spread it out, for best results, till
the compost into the top 8 to 10 inches of soil. To keep a good
thing going, follow up the initial application each year with 10
to 15 pounds of added compost per 100 square feet.

Compost will help give you your best garden ever. It will help
you have a richer, more rewarding gardening experience.

(Darbie Granberry is an extension horticulturist with the
University of Georgia College of Agricultural and Environmental
Sciences.)