Are Soil Amendments Really Necessary?

[Andrew Spiering]

There are many schools of thought on the need for soil amendments. One camp says that soil amendments are necessary for plant health and that it should always be used. While another would argue that it is better for plants (in the long run) to adjust to native soils as quickly as possible by not adding any soil amendments.

What do you think?

[Kevin J. Gaughan]

Another might even argue that you should be using a plant that is native to that soil in the first place. Saying that…we often spec soil amendments on almost every job. I, however, do not think this is necessary…the times where the amendments become most critical are when you are dealing with planting in fill (often the fill is not of the best quality and rarely matches the soil native to the site).

[Tes Lavega]

In the Middle East context where the water is scarce or if not expensive, we opt for the application of soil amendments on some projects. It reduces the water consumption or the daily water requirements by 30-40%. Here all plants has to be irrigated for establishment, exotic or endemic plants that are to be planted. And only in the established period that irrigation can be reduced. I find this a bit perplexing, that irrigation here is calculated on the same constant for all plants- whether it is exotic or endemic to the area.Tried talking with the irrigation engineers of having the varying constant for the exotic and endemic, but “it goes against there rule of thumb.”

[Ardis Ashton]

We as professionals need to look at the soil as a living organism rather than a medium for plants. If the soil is full of life (Fungus, Bacteria, Insects – FBI) then any plant will have access to the nutrients it specifically needs, whether it needs a lot like a vegetable garden or very little like a native plant restoration. If there is good soil health then amendments aren’t that necessary. If soil is sterile from being under a parking lot for 20 years then it needs a lot of amendment. Not just fertilizers and compost but mulch (sheet mulching rocks – google it up) and soil innoculants. (Harmony Farm Supply in Sebastopol, CAl).

Another approach is to build soil over time with a succession of plantings (from pioneering annuals to long lived trees over a 10, 100, 1000+ year plan) For this check out James Corner’s concept for the Fresh Kills Landfill.

[John Black]

Obviously each site’s soil is unique, and even “native” soil is rarely native unless you’ve got a preserved site. I almost always recommend a complete analysis of soil structure, biology and fertility from a lab which can recommend amendments based on the desired vegetation (including amendments to avoid, e.g. zinc in acidic soil). But there’s only so much we can do: clay-averse plants will never “adjust to” clay, just as hydrangeas will never bloom blue in alkaline soil; so the responsibility is ours to know the facts of the site and manage our clients’ expectations accordingly re: plant selections as well as maintenance.

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