Organic fertilizers explained

In my last column, I discussed fertilizer use in general, with a little more attention paid to chemical fertilizers. This week, let's take a look at organic fertilizers and why they are, or are not, superior.

First, keep in mind that your plants don't immediately care whether the source is organic or nonorganic because all nutrients must be in water-soluble form for the plants to absorb them. However, your soil cares, and therefore, in the long run, so do your plants. One of the major differences between organic and nonorganic fertilizers is the speed at which the nutrients become available for plant use. But faster is not necessarily better.

Organic fertilizers are slower to release their nutrients because the microbes in the soil must work their magic to obtain that release. Because organic fertilizers in nature occur in animal and plant waste, those sources are bulky and add tilth, or humus, to the soil at the same time they are adding nutrients. This is especially important in our Rogue Valley clay or decomposed granite soils.

Perhaps one reason people hesitate about organic fertilizers is that they have to know a bit about various organic sources, while with a chemical, they can just read the bag and dump some on the garden.

For example, a gardener needs to know that chicken manure is very "hot," because a bird's urine and feces are a combined product, and therefore the manure is very high in nitrogen and can actually damage plants if it isn't allowed to age for a while. On the other hand, llama or rabbit manure can be used fresh, because it does not contain urine and is slow to break down.

Wood products, such as fresh sawdust, shavings and bark, need lots of nitrogen to break them down and will actually rob your plants of nitrogen to accomplish that natural process. Products from the ocean, such as kelp and other seaweeds, help make excellent organic fertilizer, as do agricultural byproducts such as soybean or cottonseed meal. Coffee grounds contain a good amount of nitrogen and add texture to the soil, as do worm castings.

All of this information can be overwhelming, so the makers of fertilizers help us out by combining the right organic products and selling it to us either in bulk or in a bag. They might even add some mycorrhizae, which are tiny beneficial fungi that help the root hairs find and absorb nutrients.

So the bottom line is that organic fertilizers are better for your soil because "healthy soil makes healthy plants." Organic fertilizers also are far more likely to contain the micronutrients plants need. Learn how to make your own, or buy it already made, preferably from a local source.

Two dates to put on your calendar: On Sept. 10, Cheryl Magellen will teach a class from 7 to 9 p.m. on feng shui in the home garden. Cost is $5. On Sept. 12, the entire family is invited to the free Extension Open House from 9 a.m. to 3 p.m. More details in my next column. Both events will be held at the OSU Extension Center, 569 Hanley Road, Central Point. Call 541-776-7371 for more information.

Carol Oneal is a past president of the OSU Jackson County Master Gardeners Association. E-mail her at

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