Soil Science isn't the most scintillating of subjects (and the nerd ratio can be quite high) but basic knowledge of and understanding about soil is essential whether a gardener, horticulturist, naturalist, landscape designer, botanist or forester.
Soil facts. To save time and alleviate boredom, I've collected some bullet points. • Soil is the mineral and organic matter on the top layer of the earth's surface suitable for the growth of land plants. • Soil is formed by environmental factors (water and temperature) and by organisms acting on parent rock material over time. • Soil is not the material on the earth's surface areas that are permanently covered by more than 8 feet of water. • Plants need soil as a water and nutrient source. Tiny tertiary roots are the major absorption means. • Most plants need soil as the means of support. Exceptions include epiphytes which grow in trees and have aerial roots that don't reach the ground. • Productive soil is about 50% air that alternately fills with water for use by the plant and then slowly dries out. • A fascinating, vital, complex symbiosis occurs between soil and soil organisms. And, according to Horticulture magazine, "There are more living organisms [in one handful of soil] than there are people in the world." • Healthy soil = healthy plants.
Soil for indoor gardens. The best source for indoor garden soil is a bag of top-notch potting soil from your favorite greenhouse or nursery.
Potting soil is usually an assortment of organic materials in various amounts: peat moss, perlite, vermiculite, compost, sand and lime. Potting soil for cacti and succulents should have more sand while orchids and bromeliads need a mixture of mostly chopped bark.
Read the label carefully on the bag of potting soil. Don't buy "garden soil" or "topsoil." Also, don't use soil from the outdoor garden where the soil is many feet deep and water can drain well away from plant roots.
If you're a do-it-yourselfer or have a large indoor garden, consider making your own. It's a little like cooking–assemble the ingredients, add the right amounts of each and mix. Plus, I love the feel and smell of the soil. Information on creating potting soil mixtures is in the entry below, Mix your own potting soil.
Take care of your soil. Just as in gardening outdoors, take care of your soil.
Always provide drainage. In my opinion, water-logged soil, which we now know doesn't have any air pockets, is the prime killer of indoor garden plants. Water should be able to flow out the bottom of the pot and, further, the pot should never be allowed to sit in water.
In addition, organic components such as peat moss and compost break down and nutrients get used up over time. Soil then compacts and shrinks which reduces that nice ratio of 50% air. When that happens, do one of two things.
#1. Top-dress. Gently scratch away the surface soil and replace with 1" of fresh compost. #2. Repot. Periodic re-potting is necessary even if the plant isn't pot-bound.
Finally… You could pass Soil Science 101 now but here's one last tidbit. Plants grow in soil. Soil is not dirt. According to my dictionary, dirt is "a filthy or soiling substance, such as mud, dust, or excrement."
*** This column used information from the Soil Science Society of America (wouldn't they be fun to party with?) and the books Soil Taxonomy, Wyman's Gardening Encyclopedia and The American Heritage Dictionary of the English Language.
Photo above: This healthy indoor garden uses a metal window box and contains clubmoss (Selaginella kraussiana), geranium (Pelargonium 'Black Velvet Rose') and English ivy (Hedera helix). All three plants are in individual pots with drainage holes. I check each daily and when one needs watering, I simply take it out of the window box and bring it to the sink where I water thoroughly until about 10% has drained out the bottom of the pot. I then slip the plant back into the window box.
This also appeared in the Askov American, Askov, Minnesota.
