Make it Green: ‘Measured’ tolerance is more useful than ‘zero’ for plants

Some of the fertilizers we use in our gardens are finding a home in our lakes, rivers and in the Gulf instead.

This is not a good thing, and to ameliorate this nutrient movement, many municipalities and counties are taking a zero-tolerance approach to fertilizer application. Perhaps a more measured approach would be preferable.

First, a little background

What time of the year do plants grow in Florida? I know this is a little bit of a trick question, because the tropics in general support plant growth all year long, depending on the weather. Generalizations can be made, however, and here it comes: Plants in Southwest Florida are putting on much more vegetative growth in the summer time than at any other time of the year. Is there data to support this claim? Sure. But why bother looking it up? Even a casual observer of plants observes materials leaping out of the ground from May to October.

So, question number two: When do you suppose plants are the hungriest? What time of the year are plants most able to make full use of the food they must have to grow? Would that possibly be May to October? It would.

Eating at mealtime only

Like a lot of things that seem complicated but are really quite simple once properly explained, here’s the deal on plants: To get vigorous and healthy plants in southwest Florida, you must apply food — or, that icky word, fertilizer — at just the times when they are the hungriest.

Now we learn that some of the food we are giving our plants are being used someplace else other than by our plants. The notion here is that the fertilizer is sometimes washed away from the root zone of the target plants before the plants can slurp it up. When this happens, these chemicals are now correctly labeled “pollutants” because they are in the wrong place.

This is akin to finding Tamiflu in the water supply. Recently documented, this isn’t a desirable thing, but on the other hand, Tamiflu is an essential drug for human health, so removing it from the medical arsenal doesn’t make much sense. What does make sense is this: Medical providers, armed with the information that the material is moving through the human environment, must take measures to keep the material local. They do this in two ways. They limit the application of the drug to essential cases and they are very careful about dosing.

On the fertilizer issue, along comes Lee County, making by ordinance the application of either phosphorous or nitrogen in the summer months illegal. Zero tolerance. They make a cute Web site, they have some nifty ads drawn up and, all of a sudden, we have what you call a program. Is this sensible? No, it is not, because it is not based in science.

Friends with like views

I am not alone in my view. Let’s have a look at a recent paper by University of Florida scientists called “Unintended Consequences Associated with Certain Urban Fertilizer Ordinances.”

Understand whom we are talking about here: This paper is written by professional research scientists. So often, public outreach agencies have a single, shrill mantra: “No water! Only natives! Only compost!” This isn’t the case here. These people are scientists who take a measured approach to some tough issues and do it based on research, in this case, on zero-tolerance ordinances.

This is a lengthy technical paper, but not to worry: Your faithful design reporter has waded through it for you. Here’s a summary, from the paper:

The research on this subject, however points to possible problems associated with severely restricting fertilizers on turf and landscape plants during their most active growing period on sandy and/or compacted soils with low nutrient- and water-holding capacities. These unintended consequences could result in increases in nutrient application, increases in nutrient leaching and run-off into water bodies, and increased soil erosion, among other problems…

The paper goes on to cite a series of “unintended consequences” of fertilizer blackout periods:

* Turfgrass will decline in vigor, leading to an increased leaching of nutrients at all times of the year.

* Turfgrass that is not healthy will show declined soil coverage, resulting in more leaching, weeds, soil erosion, and nutrient run-off.

* Calendar-based blackout periods will encourage poor fertilization habits, because there will be a tendency to load up just before, and just after, the restricted period.

* A blackout policy ignores the remainder of the year, when leaching and runoff can also occur.

* A blackout policy ignores the critical nature of irrigation management: properly fertilized and irrigated turf is “one of the most environmentally sound plant systems available.” In fact, by using a proper moisture sensor, studies have shown that there is a “negligible loss of the soluble N applied…,” but that if irrigation is applied at 125 percent, as much as 50 percent of soluble N is lost.

Listen up

I cannot overstate the quality of research that the UF does on these issues, research that has been widely replicated and available for many years. In lieu of black-out periods, the UF recommends:

* Identifying more closely when and how much fertilizer is required;

* Encouraging people to apply fertilizers in a knowledgeable way: “We believe good habits will come if the regulation is reasonable and defendable from a science basis, and if individuals have been properly educated about the issues and best management practices.”

In other words, there is a solution that not only dramatically reduces fertilizer runoff, but also allows us to have strong turf and landscape plants.

Good idea.

See my Web site for more links and background information: www.msadesign.com (click on “blog” at the upper right corner). And please let me know your views, either by e-mail to ms@msadesign.com or by commenting on this column.

Finally, are you on my newsletter mailing list? Just drop an email to subscribe@msadesign.com and I’ll be sure you are.

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