Journal: Contributing Factors For A Bluebonnet Bloom (Part IV): The Texas Hill Country - January 18, 2020

In Part I of this series we discussed the factors which contribute to a successful bluebonnet season. In Part II we looked at weather data from the Big Bend in West Texas and in Part III we looked at weather data from South Texas. In the fourth and final part of this series we will look at the weather data from Llano County in the Texas Hill Country for the 2010, 2012, and 2019 bluebonnet seasons.

When people think about bluebonnets in Texas, they probably call to mind the Texas bluebonnets (Lupinus texensis) in the Texas Hill Country. Though they can be found in various places within the region they are most concentrated in the Llano Uplift, which includes Llano County and parts of Blanco County, Burnet County, Mason County, and San Saba County. Llano County, however, is the center of the north Hill Country bloom.

Llano County weather data
Rainfall and temperature data from Llano County for the 2010, 2012, and 2019 bluebonnet seasons. Green indicates a wetter than average month, red indicates a drier than average month. Blue indicates a cooler than average month, orange indicates a warmer than average month.

Similar to South Texas, the Texas Hill Country saw abundant rainfall throughout the fall of 2009 and winter of 2010. Llano County had only one month in which the rainfall total was below average (December), and it was only a quarter inch below average. Temperatures were below average throughout the bluebonnet development season except in November. The only thing that this data seems to indicate is that above average rainfall and below average temperatures are both conducive to a good bloom. It does nothing to inform us about the importance of rainfall timing during development.

The 2019 bluebonnet bloom in Llano County was not nearly as good as the 2010 bloom, though there were pockets of land that were blooming beautifully. However, it did not live up to the expectations that had been created during the fall of 2018, which saw large quantities of rainfall. Looking at the overwhelming amount of rain that fell in September and October of 2018 we can see that it was even more than fell during the fall of 2009, and causes one to wonder if there might have been too much rain. If seed germinated in wet, boggy areas, then it stands to reason that they would not have been able to develop properly and could have died from fungal disease. We see that this abundant fall rain was followed by a much drier winter, with rainfall in January about average, and then below average in February and March.

Temperatures were the inverse of what one would expect is needed for optimal development, below average during the germination period and above average during rosette development. I believe it is these factors that combined to deliver a bluebonnet season that was less that what had been hoped for.

2019040103, Texas bluebonnets at dusk

A field of Texas bluebonnets (Lupinus texensis) and rolling hills at dusk in Llano County in the Texas Hill Country during the 2019 bluebonnet season. Prints and licensing available.

The 2012 bluebonnet bloom was the second best bloom of the decade in Llano County, but if one only looked at the weather data one would have had difficulty predicting it. Rainfall was below average during the germination period, however, only slightly so in October. Then, it was above average during rosette development. This seems to indicate that October is the most important month for rainfall during the seed development period. It also seems to indicate that above average rainfall during rosette development is very important if rainfall is at or below average during the germination period.

Temperatures, meanwhile, were above average every month except for December, which seems to indicate that rainfall is a more important factor for successful bluebonnet development than temperature.

Overall, the data indicates that above average rainfall and below average temperatures are optimal for bluebonnets, but that a variety of conditions can combine to produce a successful bloom.

Sources

Climate at a Glance. (n.d.). Retrieved from https://www.ncdc.noaa.gov/cag/county/time-series

Merlo, J. (2020, January 11). Contributing factors for a bluebonnet bloom (Part I). Retrieved from https://www.jasonmerlo.com/gallery/contributing-factors-bluebonnet-bloom-texas/