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Guide to Avoid Pointless Soil Amendments

This quick guide will help you avoid soil amendments products that are expensive, pointless, and sometimes harmful to you, your garden, and our environment.

Bioenhancers are products that usually include kelp extracts and “secret recipe” ingredients meant to boost plant growth but, in reality, they provide few nutrients. Proponents swear these products improve plant growth and enhance resistance to environmental stress, pests, and disease, but science has shown few, if any, of these benefits are realized. Researchers conclude that proper plant selection and management contribute to success more than any of the bioenhancers tested, leading a 2002 Virginia Tech study to say, “claims for the benefits of these products go beyond what is substantiated by the research.” Far worse than wasting your money is the ecological damage done to kelp forests when they are strip-mined for this product.

Compost tea originally was touted as foliar spray for fighting plant disease; more recently it’s been advertised as a way to add beneficial microbes and nutrients to build healthier soils. While your grandmother probably made an old-fashioned “tea” by merely collecting the water that ran through her compost pile, modern compost teas are constantly aerated in large brewers with carefully regulated additions of microbes and nutrients. It’s all very scientific-sounding, but definitely an example of the emperor’s new clothes. These products just don’t work. There are many peer-reviewed studies on aerated compost teas, but none has shown a consistent effect either in disease suppression or improving soil health. Since we’re all interested in working with nature, why not use compost as a mulch and let nature brew her own tea? Not only is it more natural, but it’s also cheaper.

Phosphate fertilizer is promoted as a root stimulant and flower enhancer, and while phosphate is often needed for intensive agricultural production, most home garden soils contain this nutrient. In fact, gardeners who use phosphate fertilizer willy-nilly run a serious risk of creating toxic levels of phosphorus in their soil. Excess phosphorus can inhibit plants’ iron uptake, causing leaf chlorosis; it also inhibits beneficial mycorrhizal fungi from colonizing roots. This unhealthy soil condition makes plants more susceptible to opportunistic pests and diseases. On a larger scale, unused phosphorus often ends up downstream, contaminating aquatic systems. Before you add phosphate (or any fertilizer), be sure to have a soil test done to determine if you need it.

Epsom salts have to be the best example of a marketing spin I’ve ever seen: Epsom salts is simply magnesium sulfate, two chemical elements found in all soils. Gardeners, however, especially rose aficionados, routinely use Epsom salts in an effort to enhance plant growth. Certainly, magnesium and sulfur are minerals required by plants, but most garden soils aren’t deficient in either; adding too much of either can create nutrient imbalances that hurt plants and other soil life. The only scientific research that supports the use of Epsom salts is in intensive crop production where depleted soils can become deficient in magnesium.

Mycorrhizal inoculants contain mycorrhizal spores and sometimes fertilizers. Mycorrhizal fungi are definitely a gardener’s best friend. These products are not. Research shows that inoculants are only effective when applied to sterile growing media, such as that used in production nurseries. Healthy garden soils contain plenty of native mycorrhizal species; in fact, studies in peer-reviewed publications demonstrate that plants treated with inoculants do no better than untreated plants once they’re in the ground. If your soil is so damaged that it can’t support the growth of native mycorrhizal fungi, adding packaged spores is certainly not going to help. A better approach is to cover your injured soil with a healing layer of organic mulch.

Water crystals, also called hydrogels, are advertised as environmentally safe products that increase the waterholding capacity of soil. When they meet water, these synthetic polymers swell like sponges and slowly release the water to the surrounding, drier soil. You often see them in nursery potting mixes—they are clear, squishy blobs. While hydrogels work fine for short-term nursery production, they decompose with exposure to sun, fertilizer, and microbes. Some gels are toxic to aquatic life, and what’s worse, we don’t know how dangerous they are to people and animals. A thorough discussion of the potential dangers of hydrogels is beyond the scope of this article, but gardeners may wish to avoid them altogether.

Conditioners are supposed to break up clay, reduce compaction, and improve drainage and aeration. Through this process, they supposedly “bioactivate” soils. The active ingredient on the product label is ammonium laureth sulfate, commonly known as soap. It’s no surprise to hear that soap breaks up dirt. (Doesn’t it do so on your hands every time you come in from the garden?). However, it certainly won’t “bioactivate” soils; if anything, it will kill any soil-dwelling critter unlucky enough to be exposed to it.

Gypsum, or calcium sulfate, has long been used by farmers to break up heavy clay soils. It also sweetens salty soils by removing sodium. Most home gardeners, however, don’t have heavy clay or saline soils, though compaction is a common problem. Contrary to popular opinion, gypsum does not loosen compacted soils, increase water-holding capacity, improve fertility, or decrease acidity. The addition of calcium to soils with sufficient levels of this mineral, however, can create nutrient imbalances. A soil test can guide you before you add this amendment.

Crystals, tea, and conditioners sound tempting, but that doesn’t mean your soils and plants need them. Instead, I recommend using organic mulches. Not only will you save time, money, and natural resources, but you also will reduce the need for pesticides and fertilizers. Now that’s sustainable.

Organic mulch is what you need

Decades of research have shown that organic mulch creates healthy soil that supports plant establishment and survival. Compost is a wonderful mulch for vegetable gardens and annual beds and, when topped by a chunkier woody material, makes an excellent mulch for landscaping.

Here is a quick look at the benefits of organic mulch.

  • Captures rainfall and slows evaporation, thus reducing irrigation needs and preventing runoff
  • Prevents soil erosion and compaction
  • Insulates the soil, allowing roots to continue growth throughout winter
  • Slowly provides plants with nutrients as it decomposes
  • Enhances plant establishment and growth
  • Prevents light from reaching soil, starving buried weeds and preventing seed germination while doing so
  • Provides a habitat to a medley of beneficial microbes, insects, and other soil organisms, which can reduce disease and pests and, in turn, reduce the need for fertilizers and pesticides
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