Organic vs Chemical Fertilizers

Intensive food gardening is almost certain to strip nutrients from the soil, nutrients we need to put back in order to grow vegetables year after year. The question then becomes: do you use chemical or organic fertilizer and why.

Most chemical fertilizers provide only nitrogen (N), phosphorus (P), and potassium (K). While these macro-nutrients are required in greater quantity than any others, they are only three of the thirteen nutrients plants need. The three chemicals that qualify as secondary nutrients – calcium, sulfur, and magnesium – are generally ignored, as are the trace nutrients: boron, chlorine, manganese, iron, zinc, copper, and molybdenum. While these are needed in far smaller quantities than the macro-nutrients, they are still essential.

Pure chemicals can be hard on the earthworms and micro-organisms in the soil that keep it alive and working, thus making nutrients available to plants. Earthworms not only provide perhaps the best compost available, but they also help aerate soil when they tunnel through it. Without the beneficial effects of worms and micro-organisms, plants have a harder time accessing the secondary and micro-nutrients that are not found in most chemical fertilizers.

Chemical fertilizers can be equally hard on plants themselves, because they bypass the work a plant normally has to do to gain access to nutrients. Pure chemicals will make soil less nutritious, and lessen the plants’ ability to access nutrition.

Finally, chemical fertilizers are hard on the environment. Many are synthesized from oil, their production requires a significant investment of fossil fuels, and when they run off into streams or lakes, they can cause further problems. Algae blooms (the sudden growth of underwater plants) encouraged by agricultural run-off can consume oxygen needed by fish and other organisms. Fertilizer that leaches down to the water table may cause more direct threats to human health.

Organic fertilizers, far from being purified and simplified chemicals, are complex compounds that add numerous secondary and micro-nutrients beyond the one or two for which they are best known. Organics such as manures, powdered rocks (such as lime, rock phosphate, and greensand), blood meal, bone meal, wood ash and compost all contain important micronutrients and their texture will improve soil quality rather than degrading it.

Organics contain important secondary and trace nutrients; improve soil texture, aeration, and drainage; provide slow-release nutrition; aid the environment in many ways and harm it in few.

Fertilizer Formula

10 parts canola or cottonseed meal

1 part steamed bone meal

1 part kelp meal

1 part dolomite lime

¼ part blood meal (for dark greens only)

Most of the ingredients for this mix can be purchased at the garden centre. You can apply the fertilizer generously, working it into the soil under each plant. It won’t burn and it releases slowly. Use about one cup for each large plant, perhaps half that for a head of lettuce. Use about four litres per 100 square feet to prepare an entire bed. Sprinkle this mix lightly on each layer as you build your compost heap to supercharge decay. It will help break down tough material and create a very fine compost.

Adapted from Eric Vinje: Planet Natural, and Randy Shore: The Green Man, Vancouver Sun