Never use gypsum, lime
without prior research
Brian Jervis: Master Gardener
Saturday, November 26, 2016 12:00 am
Q: When is it best to apply gypsum and lime
to my lawn? D. A. Tulsa
A:
You should never use
either one without specifically documenting a reason. Gypsum has been used in
the past to improve the drainage of clay soils, and lime is used to treat
overly acidic soils.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_MaOuIbROAAfc_VSIkFvNftrzLMv3TusKbJ7ukZ-wN5_cezKisqLeSV91wcwofupwUOj97eTmba47lRu3QJjrWWNDa2NhkXkBfr8bCPWbv4cLGQxVKq3Pjo4EPtZXEt0eiTvtiksFFq7a/s200/11-26-16_bag+of+lime+for+lawn_Forestry+Images.jpg)
Clay particles are so small and flat they pack
down and present a barrier to water, nutrients and plant roots. Tactics to
loosen these soils have been researched thoroughly and gypsum, along with other
materials, has been shown not to be useful. The OSU handbook, E-1003, “Oklahoma
Homeowner’s Handbook for Soil and Nutrient Management,” explains the origin of
the gypsum myth.
Gypsum is appropriate to treat soils with
calcium or sulphur deficiency, but this is not likely in our area. Gypsum is
also useful to treat “sodic” soils, or soils that have been exposed to
excessive amounts of sodium containing salts. These soils need to have the
salts removed to be plant friendly. The calcium in gypsum will displace and
correct the salt excess.
The ideal approach in dealing with heavy clay
soils is to use raised beds. If raised beds are not an option, regularly
tilling large amounts of organic material will improve the tilth of clay soils
as it does with all other soil types.
The use of lime is useful but should always be
based on the pH (measurement of the level of acidity) result of a soil test.
Lime, which is calcium carbonate, will raise the
pH in soils, making it less acidic. The pH of soil is a result of several
factors, one of which is the amount of rainfall. Rain filtering through soils
tends to remove calcium and add hydrogen. Hydrogen in soil increases acidity;
calcium reduces it. The more rainfall, the more likely the soil will be acidic.
Often people who are from states east of us will
assume liming is needed regularly, as it was often needed there, but that is
not the case in most of Oklahoma.
Average yearly rainfall in Oklahoma drops
steadily from our eastern border to the panhandle. Because of this, on average,
there is less soil acidity from east to west.
Most plants perform best in neutral to slightly
acidic soil; this includes most turf grasses. According to the USDA, the
optimum pH for fescue and Bermuda is acidic, in the range of 5.5 to 7.0. Our
average pH in the Tulsa area, based on more than 1,000 soil test results
performed by OSU is 6.8, which is favorable to turfgrass and other plants. So,
on average, no lime is needed and if used might be harmful to your grass. A
soil test will inform you of a need for lime.
Garden tips
§ Fertilize cool-season grasses like fescue with 1
pound nitrogen per 1000 square feet. This should be the last fertilization for
fescue until next spring. Do not fertilize Bermuda or Zoysia until green-up
next April.
§ Spring-flowering bulbs like hyacinth, narcissus
and tulip, which are sold for “forcing,” can be potted indoors for a colorful
winter display.
§ Tulips can still be planted outdoors through
this month.
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