The Passionate Gardener: May 2016
Some Common Gardening Products Explained
By: Ron Kushner
Light-colored, finely powdered rocks or pellets containing calcium sulfate. Gypsum improves packed-down and clayey soils for water penetration (drainage) and aeration by making the fine particles of clay stick together and neutralizing the salt in high-sodium soils without raising the pH as lime does. The process is a chemical one, whereby sodium ions are exchanged for calcium ions, which separates the clay particles enough to create “pore space” for air and water. Because it is a neutral salt , may be used where you want to increase soil calcium without raising the pH. I use a handful with every tomato plant as a deterrent to blossom end rot. It not only adds calcium but sulfur also, both secondary nutrients.
Gypsum has been used since the days of the early Greeks. It comes in pelletized form which is easier to use than the powder form.
Also known as ground limestone, limestone, agricultural lime and garden lime. The chemical name for lime is calcium carbonate and comes in a variety of forms. It is commonly mixed with magnesium carbonate. It comes bagged as a fine white powder, granules of ground limestone and most commonly as pellets.
When mixed with magnesium (which is quite common) it is called dolomite or dolomitic lime. Most articles recommend dolomitic lime to be used for your lawn and garden but today it hardly matters. It used to be that there was a lot of hydrated, or slaked lime on the market along with “builder’s lime” that was very caustic, dangerous to handle and designed to be used in construction materials such as mortar and plaster. These products are much more concentrated and will burn plants. Fortunately, they are not commonly available in garden centers or nurseries so there is little cause for concern.
Lime is primarily used to raise the pH of soils, to make them more alkaline, or sweeter. The lime neutralizes soil acidity so that microorganisms can help break down organic matter into humus. However, it is helpful in many other ways as well. It is not considered a fertilizer but it helps in the release of nutrients and improves the structure of clay soils by increasing moisture retention and drainage. Lime also helps control club root, a disease found in plants of the cabbage family and tends to prevent moss growth.
Most lawns in our area require at least an annual liming and in acid soils liming is necessary to grow many perennials and vegetables. Always depend upon an actual soil test to determine how much (if any) to apply. My own garden in Lafayette Hill has a pH of 7.1 and has never required lime. This is not normally the case in this area.
Greensand is a pulverized rock powder, also known as “Glauconite”. It is mined naturally from marine deposits found near the New Jersey coast. It was called “granite dust” years ago as it was really just crushed granite. In any case, it has many trace minerals and is a natural source of potash which is great for adding to vegetable garden soil. It retards soil compaction and holds moisture. It is often recommended for roses and greenhouse potting mixtures where moisture retention and drainage are issues.
Epsom salts are a white powder, magnesium sulfate, containing almost 10% magnesium and 15% sulfur. It is a good source of magnesium when a soil test indicates it is needed. Usually, lawns that require magnesium get it quicker with an application of lime. Epsom salts get their name from a mineral spring in Epsom, England where they were first collected.
Perlite is a white, light, hard, porous, gritty material that looks like tiny white balls. It is formed when lava (volcanic rock) is heated to a high temperature, which causes it to expand. It is nontoxic, sterile and odorless. It can be used as a rooting medium on its own. In soils it increases drainage, improves aeration and decreases the weight of potting mixes. It also helps to retain water, which attaches to the particles’ surface. It is commonly found in most bags of soil-less potting medium.
Vermiculite is an extremely lightweight, granular substance with grains about 1/16 inch in diameter. It is formed when mica chips are heated to a high temperature and expanded (actually, popped like popcorn!). It contains some potassium, magnesium and calcium which are slowly released in soil.
It is commonly used in soil mixes to increase the water and fertilizer retention of the mixture, as well as to lighten and open it up. It is commonly used as a soil amendment of vegetable containers and beds, a rooting medium and for seed starting. Avoid adding it to very clayey soils as the clay bonds with the vermiculite, instead of the vermiculite breaking up the clay.
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