If applied regularly and in sufficient amounts, compost or wood chips could provide all the nutrients your plants need.
If applied regularly and in sufficient amounts, compost or wood chips could provide all the nutrients your plants need. (Lee Reich, The Associated Press)

To get the most out of any organic fertilizer, you need to keep in mind two chemical processes: how plants take up nutrients and how such fertilizers act in the soil — in other words, the where, when, and what of organic fertilization.

1. Where

The bulk of a plant's feeder roots — whether it's a mere marigold or a mighty oak — lie just beneath the surface. That means generally, there is no need to dig fertilizer deep into the soil. Low oxygen levels there retard microbial growth, anyway; that microbial growth is necessary to unlock the nutrients from most organic fertilizers.

An exception to that "no need to dig" rule is when phosphorus levels are low, as indicated by a soil test (or stunted plants that are purplish when young or late to ripen). Cold soil in spring also can cause a phosphorus deficiency, a temporary one that abates as soon as soil warms and roots start reaching out.


Once the soil is up to snuff with phosphorus, periodic surface applications of fertilizer can trickle down through the soil fast enough to maintain adequate levels throughout the root zone.

2. When


When should you apply organic fertilizers? Remember that the nutrients in most of them are initially insoluble and in forms that plants cannot use. This means you need to account for the time lag between application and nutrient release by spreading organic fertilizers a few weeks before planting. (You can even do it a few months before planting, or way back late last fall.)

Because soil microorganisms need time, warmth and moisture to release the nutrients from organic fertilizers, plants may have to wait to eat in dry soil. Of course, plants grow don't grow much in dry soil, so their fertilizer needs are less. Watering not only quenches a plant's thirst, but also makes food available.



But consider these quick-acting fertilizers as quick fixes only. Build up good reserves of nutrients in your soil, and such applications will be unnecessary.

The slow action of organic fertilizers is really a benefit. You only need to apply them once a year and, because heat and warmth spur microbial activity and plant growth, the nutrients are released in sync with plant needs.

3. What

Spreading an inch of compost or a few inches of leaves, wood chips or some other organic mulch over the ground each year will provide all the nourishment many plants need.

The possible exceptions — those hungriest parts of the garden — are vegetable and formal flower beds. I like to feed the ground there with compost, which is an organic material relatively rich in nutrients.

Trees and shrubs, informal flowers and wildflowers are less needy. Here, any organic mulch, from wood chips to straw to pine needles, will suffice. Over the years, the compost or other organic mulches will enrich the soil to create a spectrum of nutrients available to those plants. And it'll be a much wider spectrum that would be available from any chemical fertilizer.

In naturally poor soils (Editor's note: That would be most soils in Colorado) some additional, more concentrated, nitrogen fertilizer might be needed for a year or more until the soil is up to snuff, or new plants established. Soybean meal or alfalfa meal is usually sold as an animal feed, but sprinkled over the ground just before some organic mulch is applied, it's a convenient, nourishing and organic "feed" for plants, as well. Apply a couple of pounds per hundred square feet.