Searching for amendments to heavy clay soils

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Amending soils is often a topic discussed among gardeners in Wyoming. The typical heavy clay soils found across Wyoming provides certain growing challenges.

The challenges of clay are many such as trying to till or have water or roots trying to penetrate this hard dry material, which reminds us of trying to garden in a driveway. Although the water holding capacity and nutrient capacity per square foot is higher with clay than sand, the ability to have good plant rooting and water movement is very slow.

These characteristics then bring us to the discussion of what to do with a heavy clay soil. First item generally mentioned is adding organic material. Organic material can come in any form such as grass clippings, wood chips, leaves or compost. The more organic material added to a soil the easier the soil is to work and it allows water and air to easily penetrate, which lets the roots of plants grow easier and deeper.

The one disadvantage of adding organic material to our soils, is it has to occur on a regular basis or it is broken down into its chemical compounds and over time the structure and composition of the soil will change to a less desirable state. Another disadvantage would be in a lawn situation where it would be difficult to add organic matter.

There are some alternatives to consider which are long-term solutions to help with amending a heavy clay soil, however all soils need organic matter to grow plants. There are three main products, a slate aggregate, a shale aggregate and clay aggregate. All three of these materials are heated to a very high temperature in a kiln, which expands these soil types creating many pores. The pore space of these materials when added to our native soils adds the additional pore space for water, air and helps in preventing compaction. The advantage of pore space is it lets in air and water where sand or gravel does not necessarily help break up heavy clay soils.

The advantage to these products is you do not need to add some every year especially if you are looking at a sod or grassy area. For gardens or flowerbeds, it is advised to still add organic matter on a regular basis. This material is far superior to adding sand as an aggregate since these products have pore spaces and will not have a tendency to combine with certain clay particles to create a harder material.

These aggregates can also be used as mulch on top of the ground, with the advantage of being a lot lighter in weight than using rocks. Just as rocks or other hardscape material, they will not decompose or break down over time. These aggregates can also be used in roof top landscaping, rain gardens, or other areas needing good drainage. A local source might be scoria, the dark red lava rock seen in many areas of Wyoming. Other sources to look for are”Stalite Perma Till,” Espomais “Soil Perfector,” “Utelite E-Soil,” TXI “TruGro,” “Hydroton,” “Turace.”

So as you are looking to amend your soils keep these aggregates in mind, as a possible additive to your mix.


Editor’s Note: Trade or brand names used in this publication are used only for the purpose of educational information. The information given herein is supplied with the understanding that no discrimination is intended, and no endorsement information of products by the University of Wyoming Extension is implied. Nor does it imply approval of products to the exclusion of others, which may also be suitable. The University of Wyoming is an equal opportunity/affirmative action institution.

Scott Hininger is with the Sheridan County Extension office.


By |July 26th, 2013|

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