I recently received this ad in the mail:

While I noticed the baby crawling on the grass, the dog,  and the blurbs—“Better for you, your loved ones & your pets” and “50% less synthetics”—all designed to convey safety (with even more health references on the back), it was the word “Probiotic” that really caught my attention.

Probiotics are a hot topic. Research is constantly discovering how important our gut biomes are. But a lawn is not a digestive system. It looks impressive on the advertising, but is there really any point to putting probiotics on your grass?

First we need to clarify exactly what “probiotic” means. According to the WHO, probiotics are “live microorganisms which when administered in adequate amounts confer a health benefit on the host.” In this case, they’re presumably applying “live microorganisms” to the turfgrass. So what kind of microorganisms are our lawns lacking? Does adding more make a difference?

Lawns grow on soil. Unless you’ve sterilized your yard, your soil is already full of a wide variety of bacteria, fungi, actinomycetes, algae and protozoa. In fact, there are billions of these microorganisms in just one teaspoon of soil—adding more is pointless!

Microorganisms play an important role in creating a healthy soil structure and in nutrient availability. Their populations are always in flux, depending on food availability, soil conditions, and other factors. For example, if you till a green cover crop into your soil, those organisms that feed on fresh plant material will quickly increase. Once their food source is used up, the populations decline, replaced by organisms that feed on residual organic matter such as cellulose.

Moreover, the microorganisms already in your soil are perfectly adapted to your conditions, such as where you live, what the climate is like, and the mineral composition of your soil. Since the probiotics in this product did not come from your yard, is it okay, or worthwhile, to introduce additional, non-native organisms?

According to the University of Georgia Extension,

Introduced microorganisms must compete with those already in the soil and survive predation from native protozoa and nematodes. They must find the proper food source and environmental conditions to survive. Introduced microorganisms can be stressed by fluctuating soil water conditions, use of fertilizers … (both organic and conventional) and soil disturbance such as cultivation. Because of all these effects, introduced microorganisms may not persist for very long in the soil ….

While we’re pretty sure they don’t help, there is insufficient research that answers the question of safety. What happens if the introduced species preys on the natives? More studies are needed—anyone need a topic for a PhD thesis?

While this ad proclaims “Made for Colorado,” realize that Colorado is not a homogenous state. Some parts are desert. Others are prairie. There are mountain peaks and riparian valleys. And then there are towns and cities, with their own unique conditions. The soil in your yard, subject to construction-related disturbance, compaction, fertilizers, and more, is nothing like that found naturally. So what part of Colorado is this product made for?

Or perhaps the slogan “Made for Colorado” refers to our love of natural & probiotic lawn care, and has nothing to do with what they’re applying to the grass.

There have been a few studies designed to learn if it’s safe, beneficial, and cost-effective to add various soil inoculants. All were focused on large-scale agriculture, with lackluster results. For the home gardener, given the incredible abundance of microorganisms already living in the soil, adding more is at best a waste of money.