Here's a quick update on how I use the growth ratio tool. You can see all of this data live here.
It's my first day of the work week and always like to look at my maintenance dashboard after getting my set up for the day. Today I noticed that the growth ratio is almost exactly at 1. Essentially we have cut exactly the amount of grass that the model suggests we cut.
My old "speedo" chart above shows us growing the grass exactly the way we want it as during the winter I like to switch into a recovery growth ratio which is a ratio at or above 1. This allows our very slowly growing grass to tolerate winter traffic and disease stresses.
Note that my current growth model differs slightly from what I have described on this blog in the past. I have a modifier that makes the minimum growth potential yield set to 0.3 ml/m^2/day. This is because the grass here continues to grow despite very cool temperatures and it does not go dormant in the winter. The growth potential model has some issues as the growth potential approaches zero.
The chart above only provides a snapshot of today and makes it difficult to see the trend. It might at first seem impressive to hit the numbers so precisely but in reality it is just the point where the trendline crosses the 1 on the x axis. We have both the weekly and monthly crossing at the same time which does suggest that we are growing the grass quite consistently.
The chart below is the current chart that I use to see the trends of the 30 and 7 day running average growth ratios which is much more useful for making growth management decisions.
As you can see, the 30 day growth ratio (the most useful IMO) is tracking right at 1. We will likely cut again in the coming week and this will bump it up to above 1 which is where I want it for the winter months.
The 7 day growth ratio is also above 1 which suggests that the 30 day will continue to trend upward for the coming week with no action other than mowing required.
The PGR percent used (205 GDD) has just gone above 1 so I can also expect to see some rebound effects although they will probably not be significant.
It has also been over a month since I applied 0.45g N/m^2 on Dec 17, 2022.
What would you do to manage the growth in the coming weeks considering that we probably want the growth ratio to be at or slightly above 1?
Should I apply some nitrogen?
Should I reapply a light rate of growth regulator?
My experience tells me that I should probably do nothing at least for another week and mowing. The rebound effect of the PGR should give us a bit more growth without the nitrogen. We have also only removed about 25% of the nitrogen applied in December in our clipping yield. There is likely more nitrogen in the soil with some potential for growth.
February is our worst for growth in my climate. It consistently has the lowest growth potential sum and clipping yield as can be seen on the charts below.
I definitely do not want to suppress growth going into February because nature will do that for me! I will likely withhold PGR applications until the growth potential starts rising again and I am sure that I don't need a recovery growth ratio.
Without a tool to compare your actual growth rates to a standard growth rate, it is very difficult to make growth management decisions especially in the winter when the growth is very low. The growth ratio tool makes it pretty easy to get the growth rate you need for good consistent and healthy playing surfaces in the winter months.
