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A Practical Approach to Landscape Plantings Associated with Lime-Stabilized Soils

Summary:
High pH conditions in low permeability, compacted lime stabilized soils do not harm plants in adjacent landscape planters with fertile soil mixtures. Water applied to the planters will migrate down and out, but not leach material from the limed soil any more than from a concrete border. Plant should be in good soils, not lime stabilized soil or concrete scrap. Thousands of healthy plants at hundreds of lime stabilized projects attest to the benign nature of lime stabilization.

Background information:

1) Plants require a fertile soil as an hospitable growth medium, including:

a) Granular minerals with a texture that permits aeration, root penetration, growth and anchorage.

b) Organic material that promotes ion exchange and water retention for sustenance.

c) Adequate water supply of good quality.

d) Supply of major and minor nutrients and trace elements in an accessible form.

2) Lime stabilization of soils is a construction process, which:

a) Raises the pH of the clayey soil.

b) Converts the clayey, plastic soil to a compacted, load-bearing mass.

c) Increases the particle size while reducing the porosity and permeability.

d) Causes calcium to dominate the cation exchange sites and trace elements.

Observations:

1) The texture and pH of freshly lime stabilized soil is like concrete scrap.

2) Lime stabilized soils are relatively impermeable as reflected in the hydraulic conductivity,1 which is about the same as required for impermeable landfill liners.

3) In planting areas, lime stabilized soils are replaced with a suitable planting soil mixture.

4) The pH of lime stabilized soils decreases to a range compatible with plant life as the pozzolanic and recarbonation reactions consume the excess lime and form calcium carbonate, limestone.

5) Concrete curbs or liners are generally cast in place, separating the plants from lime-stabilized soils.

6) Planters generally have deep, permeable soil and are watered regularly. Lime stabilized soils are compacted to a low permeability and covered with asphalt or concrete. While water flows are generally downward, any horizontal flow would be from the planters to the limed soil. Plants are not affected.

7) Around the world and for decades, in hundreds of projects and thousands of healthy plants demonstrate that there plants are compatible with lime stabilized soils. The plants thrive in appropriate planting soils adjacent to the durable, strong compacted base material made of lime stabilized soils.

Average Hydraulic Conductivity of Water Amended with Various Amounts of Lime. (cm sec-1)

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References:

1) Omidi, G.H., Prasad, T.V., Thomas, J.C. & Brown, K.W., 1996, The Influence of Amendments on the Volumetric Shrinkage and Integrity of Compacted Clay soils Used in Landfill Liners, Water, Air and Soil Pollution, Vol. 86, pp. 263 – 274.