Journal: 2021 Bluebonnet Forecast (Part II) - South Texas

February 6, 2021  |  South Texas

In Part I of this series we took a look at the rainfall and temperature data from the Big Bend in West Texas. In Part II we will look at the weather data from South Texas. For the purposes of this article, South Texas is defined as Atascosa County, DeWitt County, Gonzales County, Guadalupe County, Karnes County, and Wilson County. Although there are certainly plenty of other areas of South Texas where bluebonnets bloom, these are the areas with which I am most familiar.

The 2010 bluebonnet season is the benchmark by which all other South Texas bluebonnet seasons are judged. It was termed by one person at the time as the best bloom in fifty years. While that may be hyperbole, the fact remains that it was an outstanding bloom. As such, the weather data from that season is presented below alongside the current data as a frame of reference for what the ideal conditions are.

Rainfall and temperature data from South Texas for the 2010 and 2021 bluebonnet seasons.
Rainfall and temperature data from South Texas for the 2010 and 2021 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.

Overall, the data shows a warmer and drier than average year, which is not good news for bluebonnet lovers. But, the data above doesn't tell the whole story, so let's look at the departure from normal rainfall maps for more detail.

Seed germination period

Rainfall during what I term the seed germination period is the most crucial time for rainfall during bluebonnet development. The germination period runs from sometime in September to sometime in November.

September 2020 departure from normal rainfall in South Texas.

September 2020 rainfall shows a very promising start for bluebonnet seed germination, with the majority of the area in question receiving well above average rainfall. What is not apparent from the map is when in September the rain fell. Late in the month would likely be more favorable than early in the month.

October 2020 departure from normal rainfall in South Texas.

Unfortunately, after a great start in September, the weather took a 180 degree turn. The region received anywhere from two to four inches below the normal amount of rainfall. As noted in the table above, between .10 and .30 was all the rain that fell across the area. This was a significant blow to the bluebonnet seeds' chances at germination.

November 2020 departure from normal rainfall in South Texas.

November rainfall was average across most of the area, with the majority of Wilson County seeing a half inch to two inches more than normal. As with September, when this rain fell is meaningful, with early in the month likely being more beneficial for seed germination than late in the month.

Rosette development period

The rosette development period runs from sometime in November to sometime in February. This is the period when bluebonnet rosettes are going through a process known as vernalization and developing their root structure. While rainfall is still important during this time, it is not nearly as important as it is during the seed germination period.

December 2020 departure from normal rainfall in South Texas.

December rainfall was anywhere from average to two inches below average across the region. Wilson County continued to fare better than the other counties.

January 2021 departure from normal rainfall in South Texas.

January rainfall was a half inch to two inches below average across most of the region, with a few pockets of average rainfall in central Wilson County.

2021 South Texas bluebonnet forecast

Predicting a bluebonnet season is difficult to do with accuracy due to the fact that there are so many different factors are involved in a bloom that are impossible to evaluate. After seeing the rainfall data I believe that the 2021 bluebonnet season in South Texas is likely to look very similar to the 2020 bluebonnet season, which is to say, not good. The almost complete lack of rainfall in October 2020 was extremely detrimental to bluebonnet seed germination, and if no seeds germinate, it doesn't matter how much rain falls in November, December, or January. I believe that the best chance to see bluebonnets in South Texas is in Wilson County, however, I suggest maintaining low expectations so as not to be disappointed.

2019040602, Texas bluebonnets in sandstone boulder

Bluebonnets (Lupinus texensis) growing in a cracked sandstone boulder in San Saba County in the Texas Cross Timbers. Prints and licensing available.

In Part III of this series we will take a look at the data and forecast the 2021 bluebonnet season in the Texas Hill Country. Stay tuned...

SOURCES

Climate at a Glance. (n.d.). Retrieved February 06, 2021, from https://www.ncdc.noaa.gov/cag/...

Merlo, J. (2020, April 13). 2020 Bluebonnet Season Review. Retrieved from https://www.jasonmerlo.com/gal...

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/

Merlo, J. (2020, January 16). Contributing factors for a bluebonnet bloom (Part III): South Texas. Retrieved from https://www.jasonmerlo.com/gal...

NOAA. (n.d.). Advanced Hydrologic Prediction Service. Retrieved from https://water.weather.gov/precip/#

Regner, G. (n.d.). 2010 Texas Wildflower Sightings Report. Retrieved February 06, 2021, from http://www.texaswildflowerpict...

Vernalization. (2019, December 17). Retrieved from https://en.wikipedia.org/wiki/Vernalization