LEACHING from THE GARDEN SPOT
by Mort Mather

A month ago I wrote about slugs because we had been having rain for a week. As I look out at a garden that looks like a rice paddy I realize I can't do that column again. How about leaching?

When there is this much rain all that water has to go somewhere. First it saturates the plants. Just as it remains dry under trees during a light shower, the smaller plants have to become saturated before rain reaches the ground. Then the ground gets saturated. Then the water in and on the surface of the ground starts to move. The water in the ground moves deeper replenishing groundwater supplies. The water on the surface starts to run-off, pondding in low areas and swolling streams and rivers. Where the water ponds, as in my garden, it will eventually seep into the soil as the water below seeps deeper.

The water picks up anything that is soluble in the soil and even carries small particles of soil. Particles of soil moving on the surface are seen as erosion. If there is erosion in your garden, there are several actions you should take. Always plant across even a gentle slope, never run rows up and down hill. Mulch is a wonderful means of controlling erosion. If the slope is greater than gentle, you should consider terracing. Make your garden into a series of level steps running across the slope.

The water that seeps into the soil is also a problem, especially in the spring and early summer. Plants need water soluble nutrients. Conventional commercial fertilizers are all water soluble. Rains like we have been having literally wash the fertilizer out of the soil. This is called leaching.

Organic or natural fertilizers will also lose water soluble nutrients but the loss won't be as great. If you have compared bagged natural fertilizer to chemical fertilizer, you have seen that the nitrogen-phosphate-potassium (N-P-K) on the natural fertilizer is generally much lower than on the chemical fertilizer. It might be 5-3-4 for example versus 5-10-10 or higher for chemical. This is the percentage of soluble nutrient in the bag.

The rest of the stuff in the bag in natural fertilizer is organic material that is food for soil microorganisms. In the chemical bag it is inert ingredients. The organic material and the microorganisms do not leach out of the soil nor are they very likely to be carried away by runoff though some organic matter may float away. The microorganisms keep right on breaking down organic matter into soluble nutrients. That is the beauty of organic fertilizers. The advocates of chemical fertilizers talk about how much more potent their fertilizer is and how less has to be spread. They will also tell you about side dressing—adding fertilizer during the growing season. Organic fertilizers can be added during the growing season, too, but if you have a good organic soil going, I can't see any reason to do it.

There is one other concern over the leaching of garden chemicals (this includes N-P-K in a natural garden). Where do the chemicals go? Into the ground water, of course. This is not likely to be a detectable problem in non-farm areas though the amount of chemicals spread on lawns is horrendous and is certainly a potential problem. Children have died from nitrates from farm fertilizers and from poor stockpiling of manure which showed up in the farmer's well water. The chemicals on lawns probably do not become a detected groundwater problem because in areas where there are a lot of these chemicals the residents are on municipal water. I shudder to think of the damage lawn chemicals are doing as these torrential rains sweep them into our lakes, ponds, streams, rivers and estuaries. This is the time of year when the lawns have the most of these chemicals on the surface and available to be carried off.

ŠJune 14, 1998

Mort is a husband and father. He authored a book, Gardening For Independence and was named Environmentalist of the Year by Down East Magazine in 1987. You can eat his organic produce at his son's southern Maine restaurant. His address is 802 Bald Hill Road, Wells, ME 04090.