Getting Gipped with Gypsum?

Gypsum has long been used as an enhancer to compacted soils and to improve the quality and absorbency of soil in gardens. But there are mixed reports and significant controversy about the benefits of gypsum. Some researchers and horticulturists say gypsum is more hype than help; others say that gypsum is an effective soil enhancer and source of plant micro-nutrients that is very beneficial to gardening.

Gypsum (also known as CaSO4 - Hydrous Calcium Sulfate) is a naturally occurring, crystalline substance that's readily found in the mid-western United States and elsewhere in the world. Research suggests that when soil has been exposed to too much salt, either from coastal exposure, the use of salt-based fertilizers or winter road salting, it tends to become less permeable to water. This is typically not a problem in coastal areas where sandy soil exists, so it's not really an issue on the East End of Long Island.

However, excess sodium in the soil can exclude the uptake of nutrients such as calcium, magnesium and sulphur. Too much uptake of sodium by a plant can cause toxic reactions that are typically manifested by necrosis of leaf edges (yellowing/browning). An application of gypsum to the soil has been shown to help exclude the uptake of too much sodium by roots because the gypsum calcium ions outnumber the sodium ions in the soil.

When soil pH tests are less than 5.8, calcium levels in the soil also test low or moderate. There are instances, however, when the soil pH value will be adequate (between 5.8 and 6.5) yet the calcium level will still test less than the optimum high. Gypsum can help to remedy this situation.

Gardeners typically add lime to soil to add calcium and raise the pH value. While this is important with acidic soils, it can cause other problems, such as micronutrient deficiency. The thought is that gypsum adds the needed calcium without altering the soil's pH value.

Opponents of gypsum as a garden remedy suggest that it increases the naturally high calcium content of soils - since plants already have all the calcium they need, added gypsum doesn't improve plant growth or health.

As far as relieving soil compaction, some researchers suggest gypsum has no effect because the loosening of soil is a physical process, not a chemical one. They recommend amending soil with the addition of compost, peat and some gypsum. The addition of a two-inch layer of organic enhancers as well as gypsum, has been shown to be beneficial to most soil.

There are no easily accessible guidelines regarding the application rate of gypsum in a garden. It is sparingly soluble, so it is nearly impossible to over-apply. The typical recommendation is that homeowners use about 100 pounds of gypsum in addition to compost, peat or leaf mold. It takes about two years to see the true benefits of gypsum application.

Of course, the secret to good soil is the use of organic materials and amending soil over time. But gypsum can be beneficial, and it's safer to use than lime. The use of gypsum over time at Rock Cottage suggests that it can reverse the negative effects of using too many salt-based fertilizers. However, it is not the panacea for all gardening ills as some claim, though it is worthy of consideration.

You can contact Lance Brilliantine with any questions or comments at GardenLance@yahoo.com.

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