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The Homeowners Column
Sorting Soil Amendments
State Master Gardener Coordinator
As gardeners we always want to add something to the soil. Like frustrated cooks looking for the perfect chili recipe, we add a bit of this and touch of that. Before adding anything, it is best to get to know your soil. So tonight put your ear to the ground and listen carefully.
Ok, just kidding on that one. First get to know your soil by getting a soil test to determine nutrient levels, pH and organic matter. Labs are listed in the yellow pages.
How well does your soil drain? To determine drainage, dig a hole 8-10 inches deep. Fill it full of water. The water should penetrate the soil at least one inch an hour. If not, then you have poorly drained soil.
Generally you can't go wrong by adding organic matter. It adds important nutrients and microbes to the soil. It helps to add drainage to clay soils. Think of feeding the soil rather than feeding plants with fertilizer. If possible add organic matter to whole gardens rather than just the planting hole. Good soil in the planting hole but lousy soil all around encourages plant roots to stay in their happy planting hole never to venture out into the cruel world.
However, some plants grow better without a lot of organic matter. Perennials with runners or rhizomes can get down right invasive if they are planted in rich soils. Lavender prefers a sandy rocky soil.
Some common products to add organic matter to the soil:
Peat Moss - Peat moss is partially decomposed sphagnum moss. When purchasing peat moss, look for sphagnum peat moss not sphagnum moss. Sphagnum moss is the dried plant used in crafts and floral arrangements. Michigan peat and peat humus are usually too decomposed.
Coco fiber - Coco fiber is an environmentally sound byproduct of the coconut industry. Coco fiber is sold in bricks, literally the size of house bricks, which are easy to transport. Once wet the coco fiber swells to 3 cubic feet. Both peat moss and coco fiber are free of weed seeds and diseases. Both hold nutrients and water in the soil. Apply warm water and wait at least on hour to wet products thoroughly.
Compost – ah, the elixir of the garden gods also known as black gold. It adds important nutrients and microbes to the soil. It's also the best solution for trying to improve the drainage of clay soils. The Landscape Recycling Center 1210 East University in Urbana has great compost. PH: 344-5323.
Sand - Sand in the proper volume can add soil aeration but no organic matter. If sand is used, it should be the coarse construction grade sand not fine silica sand. Sand must be added in large quantities, at least the same quantity of soil as to sand, in order to help soil drainage. For example, use eight inches of soil to at least eight inches of sand. Sand works well in lavender flower beds.
Perlite and Vermiculite - - Perlite and vermiculite are best reserved as container soil amendments. In the garden both materials breakdown quickly and lose their benefits.
Wood ashes - Wood ashes are high is potassium and can be used in gardens. However wood ashes are alkaline and will raise the soil's pH if used every year. The soil should be tested every 5-7 years to determine the soil pH. Charcoal grill ashes should not be used in the garden due to the chemicals used in the bonding process.