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GYPSUM USE IN HOME GARDENS AND LANDSCAPES

Authors:
GYPSUM USE IN HOME
GARDENS AND LANDSCAPES
Linda Chalker-Scott, Associate Professor and Extension
Horticulturist, WSU Puyallup Research and Extension Center,
Washington State University , and Rich Guggenheim,
Horticulture Extension Educator, Canyon County Extension,
University of Idaho
FS307E
Photo Credit: James St. John
WSU EXTENSION | GYPSUM USE IN HOME GARDENS AND LANDSCAPES
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Gypsum Use in Home Gardens and Landscapes
Abstract
Gypsum has long been promoted as a soil
amendment for home gardeners who wish to
improve their soil structure. Popular books and
websites claim that gypsum will loosen compacted
soils and improve drainage. Gypsum is also claimed
to reduce soil acidity and cure blossom end rot.
Many of these claims are not supported with
scientific evidence. This publication will review the
scientific research behind the use of gypsum in
home gardens and provide readers with a set of
guidelines designed to improve problem soils and
promote plant health.
What is Gypsum?
Gypsum, or calcium sulfate, is a naturally occurring
mineral consisting of calcium and sulfur
(CaSO4, Figure 1). It is moderately soluble in water,
releasing positively charged calcium ions (Ca+2
cations) and negatively charged sulfate ions (SO4-2
anions).
Figure 1. Commercially available gypsum intended for garden
use. Photo by Rich Guggenheim.
What role does calcium play?
Calcium is an essential plant nutrient, required for
cell membrane function as well as for cell wall
structure. Calcium’s availability to plants is
influenced by the cation exchange capacity (CEC)
of soil, in which both clay and organic matter can
bind and release calcium. In this way, calcium also
plays a role in building soil structure by binding
clay particles together into aggregates. Soil
aggregates improve water movement by increasing
soil porosity.
What role does sulfate play?
Like calcium, sulfur plays an important role in plant
nutrition as an essential component of proteins.
Elemental sulfur (S) can acidify soils when it reacts
with soil water to form sulfuric acid (H2SO4). The
sulfate ion found in gypsum, however, does not
form sulfuric acid in the soil and has no effect on
soil pH.
Benefits of Gypsum Amendment
Documented Benefits
There is a robust collection of research articles on
the agricultural use of gypsum. This literature has
been recently reviewed elsewhere (Casby-Horton et
al. 2015; Zoca and Penn 2017). In general, the use
of gypsum on sodic (sodium containing) soils and
some heavy clay soils is beneficial to soil structure
and to plant health.
Gypsum can improve sodic soils, where excessive
levels of sodium ions (Na+) cause clay particles to
disperse rather than aggregate. This phenomenon
reduces soil porosity, creating poorly-drained soils
with heavy crusts (Figure 2). Because calcium can
readily bind to clay particles, the process of cation
exchange replaces sodium with calcium. The
sodium is leached through the soil and away from
plant roots, reducing soil crusts and improving
drainage. Plants benefit from the improved soil
structure as well as from the elimination of excess
sodium ions, which are toxic to most plants.
WSU EXTENSION | GYPSUM USE IN HOME GARDENS AND LANDSCAPES
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Figure 2. Salt buildup from salt-laden water percolating to the
surface and evaporating. Photo by Tim McCabe, USDA
Natural Resources Conservation Service.
Calcium’s affinity for binding sites on clay particles
sometimes improves the structure of heavy clay
soils by forming larger aggregates (peds). Peds
enhance soil drainage and aeration and reduce
compaction. In soils with a demonstrated calcium
deficiency, adding gypsum can improve plant
nutrition.
There are recent reports of possible environmental
benefits as well. When added to a clay soil, the
calcium in gypsum can bind phosphate, reducing
runoff of this aquatic pollutant (Kauppila and
Pietola 2013). Likewise, calcium can reduce
aluminum toxicity in plants growing in acidic soils
(Espejo-Serrano et al. 1999; Merino-Gergichevich
et al. 2010; Vizcayno et al. 2001; Zoca and Penn
2017).
Unsubstantiated Benefits
Most of the purported benefits of gypsum,
especially for home gardens, are not based on
scientific evidence.
Acidifies soil”: Gypsum does not change the
natural pH of soil; acidity and alkalinity are
significantly influenced by climatic factors, such as
rainfall and temperature, by local geology, and by
natural levels of organic matter.
Improves water holding capacity of soil”: Water
holding capacity of soils is closely tied to organic
matter and soil texture. Gypsum cannot change
either of these criteria, but it can increase water
movement through heavy clay soils by reducing
compaction and increasing ped formation.
Improves fertility of soil”: Other than being a
source of calcium and sulfur, gypsum has no effect
on inherent soil fertility. Plant nutrient availability
increases with increasing CEC, which is controlled
by clay content, organic matter, and pHnot
calcium.
Cures blossom end rot of tomatoes and peppers”:
This claim is based on the false impression that
blossom end rot (Figure 3) is caused by a deficiency
in soil calcium. The development of blossom end
rot is directly influenced by water stressnot by
calcium levels. There is no research indicating any
relationship between gypsum addition and blossom
end rot suppression.
Figure 3. Blossom end rot of tomatoes is not caused by
calcium deficiency. Photo by Denny Schrock, Iowa State
University.
WSU EXTENSION | GYPSUM USE IN HOME GARDENS AND LANDSCAPES
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Drawbacks of Gypsum Amendment
Without a professional soil test, it is impossible to
know the concentration of calcium in the soil, the
CEC, or pH. These are important variables in
determining what effects a gypsum addition will
have on plants or the environment. Excessive
addition or misuse of gypsum can create an
imbalance of soil minerals with unwanted results:
Gypsum can increase leaching of aluminum
and lead (McBride et al. 2013), which
detoxifies soils but contaminates nearby
watersheds (Lopez and Espejo 2002).
Gypsum can increase leaching of potassium
(Zoca and Penn 2017), iron and manganese
(Vidal et al. 2003), and magnesium (Ritchey
and Snuffer 2002; Warren and Shelton 1993;
Zoca and Penn 2017) leading to deficiencies
of these nutrients in plants on site and
contaminating nearby watersheds.
Gypsum applied to sandy soils can depress
phosphorus, copper, and zinc transport (Zhu
and Alva 1994).
Gypsum can have negative effects on
mycorrhizal inoculation of roots (Habte and
Soedarjo 1995), which may account for
reported negative effects of gypsum on tree
seedling establishment and survival (Bakker
et al. 1999; Singh et al. 1997).
Recommendations for Gypsum Use in
Home Gardens and Landscapes
There are few articles relevant to gypsum use in
urban areas, and none specific to home gardens and
landscapes. We do know, however, that urban
soilsincluding those in home gardens and
landscapesare vastly different from those in
natural areas or agricultural situations. They often
consist of abrupt layers, which are not amendable
with gypsum improvement.
At this time our understanding of how gypsum
affects soils and plants is inconsistent and
incomplete. Plant species, soil type, and rainfall
regime all interact with the physical and chemical
changes that gypsum can effect on soils (Zoca and
Penn 2017). Even in agriculture there is not yet “a
suitable recommendation that considers different
soil (type, chemical, and physical characteristics),
rainfall rates, temperature, crops, and cropping
systems” (Zoca and Penn 2017). For home
gardeners, this means there are no broad, science-
based guidelines for applying gypsum. Your county
Extension personnel should be consulted for local
recommendations based on field data, if available.
Action Items for Gardeners
Collect soil samples (as described in Fery
and Murphy, 2013) for professional testing
(Figure 4) before applying gypsum or any
fertilizer. Be sure to ask for pH, levels of
basic plant nutrients, and sodium.
Figure 4. A soil test with nutrients, pH, and sodium levels
reported. Photo by Rich Guggenheim.
Do not use the calcium-to-magnesium ratio
from your soil test to determine gypsum use.
There is no indication that this ratio is
relevant to gypsum application rates (Zoca
and Penn 2017).
Estimate your soil texture type with the
ribbon test (Cogger 2010). This will help
you determine if your clay content is high
enough (>40%) that gypsum might be
useful.
Unless calcium is deficient and pH is in the
optimal range, do not add gypsum. If sulfur
is needed, use ammonium sulfate or
potassium sulfate instead.
WSU EXTENSION | GYPSUM USE IN HOME GARDENS AND LANDSCAPES
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Use a coarse woody mulch on landscape
soils to reduce compaction, improve
aeration, and conserve soil water naturally
(Chalker-Scott 2015).
Keep vegetable gardens well hydrated
during the growing season to avoid water
stress and blossom end rot.
Literature Cited
Bakker, M.R., R. Kerisit, K. Verbist, and C. Nys.
1999. Effects of Liming on Rhizosphere Chemistry
and Growth of Fine Roots and of Shoots of Sessile
Oak (Quercus petraea). Plant and Soil
217(1/2):243255.
Casby-Horton, S., J. Herrero, and N.A. Rolong.
2015. Gypsum SoilsTheir Morphology,
Classification, Function, and Landscapes. Advances
in Agronomy 130:231290.
Chalker-Scott, L. 2015. Using Arborist Wood Chips
as a Landscape Mulch. WSU Extension Fact Sheet
FS160E. Washington State University.
Cogger, C. 2010. WSU Soil: Home Soil Sampling,
YouTube video, 9:08.
Espejo-Serrano, R., J. Santano-Arias, and P.
Gonzaléz-Fernandéz. 1999. Soil Properties That
Affect Sulphate Adsorption By Palexerults in
Western and Central Spain. Communications in Soil
Science and Plant Analysis 30(910):15211530.
Fery, M., and E. Murphy. 2013. A Guide to
Collecting Soil Samples for Farms and Gardens.
OSU Extension Fact Sheet EC628.
Habte, M., and M. Soedarjo. 1995. Mycorrhizal
Inoculation Effect in Acacia mangium Grown in an
Acid Oxisol Amended With Gypsum. Journal of
Plant Nutrition 18(10):20592073.
Kauppila, R. and L. Pietola. 2013. Gypsum to
Improve Soil Structure and to Reduce Phosphorus
Loss. Proceedings of the International Fertiliser
Society No.741 (20 pp.).
Lopez, A., and R. Espejo. 2002. Study of
Ammonium Contamination in Leachates from an
Ultisol Following Application of Various Types of
Amendment. Water, Air, and Soil Pollution
133(1):133143.
McBride, M.B., T. Simon, G. Tam, and S. Wharton.
2013. Lead and Arsenic Uptake by Leafy
Vegetables Grown on Contaminated Soils: Effects
of Mineral and Organic Amendments. Water, Air,
and Soil Pollution 224(1):1378.
Merino-Gergichevich, C., M. Alberdi, A.G. Ivanov,
and M. Reyes-Diaz. 2010. Al3+- Ca2+ Interaction in
Plants Growing in Acid Soils: Al-phytotoxicity
Response to Calcareous Amendments. Journal of
Soil Science and Plant Nutrition 10(3):217243.
Ritchey, K.D., and J. D. Snuffer. 2002. Limestone,
Gypsum, and Magnesium Oxide Influence
Restoration of an Abandoned Appalachian Pasture.
Agronomy Journal 94:830839.
Singh, G., J.C. Dagar, and N.T. Singh. 1997.
Growing Fruit Trees in Highly Alkali Soilsa Case
Study. Land Degradation and Development
8(3):257268
Vidal, M., A. Lopenj, R. Espejo, and R. Blazquez.
2003. Comparative Analysis of Corrective Action
of Various Liming and Gypsum Amendments on a
Palexerult. Communications in Soil Science and
Plant Analysis 34(56):709723.
Vizcayno, C., M.T. Garcia-Gonzalez, Y. Fernandez-
Marcote, and J. Santano. 2001. Extractable Forms
of Aluminum as Affected by Gypsum and Lime
Amendments to an Acid Soil. Communications in
Soil Science and Plant Analysis 32(1314):2279
2292.
Warren, S.L., and J.E. Shelton. 1993. Olivine: a
Potential Slow-Release Magnesium Source for
Nurseries. Journal of Environmental Horticulture
11(1):3135.
Zhu, B., and A.K. Alva. 1994. The Effect of
Gypsum Amendment on Transport of Phosphorus in
a Sandy Soil. Water, Air, and Soil Pollution 78(3
4):375382.
WSU EXTENSION | GYPSUM USE IN HOME GARDENS AND LANDSCAPES
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Zoca, S.M., and C. Penn. 2017. An Important Tool
with No Instruction Manual: a Review of Gypsum
Use in Agriculture. Advances in Agronomy 144:1
43.
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