Things to know about organic fertilizers
Before I forget to mention it again, I must caution those of you who are using Permethrin tick repellents on your clothes that this chemical is highly toxic to cats. If you spray all your outdoor clothes as I do, you might not want to have your kitty in your lap, or laying on the treated garments. I am a cat lover and very concerned about our feline friends.
Please be very careful when using this product. It is very effective, though. I have been in the woods almost every day for the past three weeks and have not seen a tick on me, whereas some of my friends have had plenty of them!
Last week, I wrote about chemical fertilizers and the fact that there are “complete” fertilizers which contain all three of the major plant nutrients: Nitrogen (N), phosphorus (P) and potassium (K). Other fertilizers may contain one or two of these nutrients, but certain soil additives, such a lime or gypsum, contain none and are, therefore, not fertilizers at all, per say. These are better described as “soil amendments.” I will write about soil amendments at a future date because they are also important.
Organic fertilizers may also be “complete” or single nutrient sources. They still must list the percentage by weight of each nutrient on the label, however. The main difference between organic and chemical fertilizers is that organic fertilizers derive their N, P, and K from naturally occurring sources and not from chemically synthesized methods. All living things contain carbon, and organic fertilizers are often derived from living things or the waste products of those living things. The most common organic fertilizer is manure. All manures contain N, P and K. Most manure products sold for gardening have an analysis of 1-1-1. Chicken manure and some other bird manures may have extra nitrogen and will have any analysis of 4-1-1 or even 5-1-1.
Dried blood is a single nutrient fertilizer with an analysis of something like 12-0-0. Other organic fertilizers are derived from plant materials, such as cottonseed meal, corn gluten meal or alfalfa. Others are made from seaweed, fish guts, rock phosphate and microbes. Rock phosphate has no carbon in it at all, yet is still considered “organic” because it occurs naturally.
The other major difference between organic and chemical fertilizers is that chemical fertilizers are formulated to be water soluble. This means that the nutrients are instantly available for the plants to utilize, whereas organic fertilizers need further microbial decomposition before the nu-
trients are available in a form that the plants can absorb. Organic fertilizers need soil microbes to break down their complex organic molecules into the water soluble forms of N, P and K. This provides a slow release source of nutrients that becomes available over a much longer period of time. Over time, the soil becomes more fertile as the decomposing organic material also adds humus and this improves the soil’s structure. Chemical fertilizers can completely leech out of the soil very quickly, if we should get lots of rain. They add nothing to the soil except for some salts that may actually be harmful over time.
It is also easy to overdose chemical fertilizers and they can burn plant roots. Four pounds of 5-1010 per 100 square feet of garden is optimal for most vegetables, but four pounds of 20-20-20 may harm them. It is much harder to burn plants with organic fertilizers. Their typically lower nutrient content such as 1-1-1 also makes it harder to overdose when applying. The only downside to organic fertilizers is that they are not readily available to plants when the soil is cold. Soil microbes are not very active when soil temperatures are below 50 degrees. In my vegetable garden I use both chemical and organic fertilizers.
I often use a reduced level of 5-10-10, perhaps one pound or less per 100 square feet, to get the plants growing quickly in the spring, plus a larger quantity of organic fertilizer, such as composted, dehydrated manure to continue to feed them in September or October. The way I look at it, is that chemical fertilizers feed the plants directly, such as would be necessary in a hydroponic system, but organic fertilizers feed the soil, and the soil feeds the plants.
Finally, resist the urge to fertilize everything that is growing on your property! Trees, ornamental shrubs, perennials and even tree fruit should only be fertilized if they need it. If they are growing well and blooming as you would expect, leave them alone!
Bob Beyfuss lives and gardens in Schoharie County. Send him an e-mail to rlb14@cornell.edu.