## A number between 0 and 1: using the turfgrass growth potential

##### 29 July 2014

Every turf manager knows that temperature has a huge influence on the growth rate of the grass. Consequently, mowing, fertilizing, overseeding, winter dormancy, heat stress of cool season grasses, and much more are all directly influenced by temperature.

I find it especially convenient to make use of the turfgrass growth potential (GP), a number between 0 and 1 that represents the proximity of the actual temperature to the optimum temperature for growth. The turfgrass GP was developed by Wendy Gelernter and Larry Stowell at PACE Turf, and their 2005 *GCM* article about GP is on my list of 5 articles every greenkeeper should read.

The turfgrass GP was the topic of my **(turfgrass talk)** column in the July/August issue of *GCM China. *In the article, I explained what GP is:

By expressing the temperature as a number between 0 and 1, we can get an idea of how much the grass has the potential to grow based on how close the actual temperature is to the optimum temperatures for growth ... At frst glance it might look complicated, but it is actually quite simple. There is a minimum value of 0 if the actual temperature is very different from the optimum growth temperature. A maximum value of 1 means the actual temperature is the same as the optimum growth temperature. The GP value, then, is simply a number that says how close the actual temperature is to the optimum temperature.

Download** Turf growth and temperatures **in Chinese or English.

If you would like to read more about GP, see:

- Turfgrass Nitrogen Requirement and Growth Potential
- Using temperature to predict turfgrass growth potential and to estimate turfgrass nitrogen use
- Growth Potential, Inflection Points, and an Optimum Temperature for Overseeding
- PACE Turf climate appraisal form (metric) with GP equation embedded
- PACE Turf climate appraisal form (US standard units) with GP equation embedded
- Understanding turfgrass nutrient requirements
- Are your greens reaching their full potential?, by Greg Evans
- Growth potential fertility: after 2 years, by Jason Haines

You can get the equation to calculate GP from temperature by downloading the climate appraisal forms above, or make the calculation yourself using the growth potential equation.

\[GP = e^{-0.5(\frac{t-t_o}{var})^2}\]

or, in an alternative formula to generate the same result,

\[GP = \frac{1}{e^{{0.5}(\frac{t-t_o}{var})^2}}\]

where,

** GP** is growth potential, a value from 0 to 1

*is the base of the natural logarithm, approximately 2.71828*

**e****is the actual mean temperature**

*t***is the optimum temperature, 20°C for C**

*t*_{o}_{3}grass, 31°C for C

_{4}grass

**is the variance which adjusts the shape of the curve, 5.5 for C**

*var*_{3}species and 7 for C

_{4}species when using °C.

If you want these equations already embedded in a spreadsheet, or want to use the Fahrenheit temperature scale, see the climate appraisal forms at the PACE Turf IPM planning tools.

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