Recipe for a Great Spring Wildflower Season

Bluebonnets and Pink Evening Primrose

What does it take to have a bountiful and colorful spring wildflower show in Texas? Most think above average rainfall during the fall months is the key.  While it is true that fall rainfall, especially between mid-September to the end of October, is critical to the germination of most of our annual spring wildflowers, rainfall is never ever the only factor. Here are the top ingredients for an awesome spring wildflower season:

RAINFALL: Just the right amount at the right time.

Fall Rainfall: For our annual wildflowers we need good average to slightly above average rainfall to help get the seeds to germinate. Nearly all of our annual spring wildflowers will germinate sometime between mid-September to early November. You have to have plants to have blooms, so with below average rainfall, the chances for new annual plants is less. Perennials also need the rainfall to ensure the future survival of their species through new seed germination.  Too much rain and flash floods can alter the balance to a point where some areas that had plants in the past will not have new seedlings and other areas will now have them that did not before.  Seeds need good contact with moist soil but not water-logged soil. Most seeds will not germinate in nature where this is standing water for long periods of time. Flash floods can uncover new seed and distribute that seed to either areas with poorer soil or to new areas with good soil as well as cover seeded areas with silt.  Too much rain can also encourage competing plants like grasses, shrubs and trees to grow and outcompete the new wildflower seedlings. Think about the tropics where, although you will find some exotic wildflowers, you not likely to see acres and acres covered with them.

Winter Rainfall: Those new seedlings have learned to keep low during the coldest part of winter, but toward the end of winter they need increasing amounts of soaking rains to help develop deep and substantial roots. Generally speaking, a healthy plant with lots of blooms is a plant with a well-developed root system.  Late winter rains are beneficial to our May and June wildflowers as well as our cool season bluebonnets.

Spring Rainfall: At least some rain needs to fall during the spring months to help keep that blooming plant blooming, but not too much rain. Bluebonnet seedlings and young plants that are in standing water for hours are susceptible to a fungal disease that results in “damping off” – rotting of the stem and root tissue. 

TEMPERATURE: Not too cold and not too hot

Warm Fall: The germination of most plants depends greatly on the soil temperature and our spring annual wildflowers need a warm soil temperature in the fall. Once the soil temperature fall below a certain level the chances of germination decrease.

Cold Winter:  Surprisingly, our bluebonnets (and most other wildflowers) also need cold winters to help encourage them to bloom more in the spring. This process is called vernalization.

Cool Late Winter: A hot or cold, but dry late winter will result in a very poor flowering for many of our early spring wildflowers. A warm wet February is equally dangerous for our bluebonnets due to the susceptibility to fungal disease. 

Warming Spring: During March, the temperature needs to warm the soil to stimulate upper plant growth or “bushing up” of the plant.  During the winter the seedlings form flat rosettes. These “rosettes” are a collection of early leaves that hug the ground during winter. The function of the rosette, is probably for protection from cold snaps and to compete with other species by depriving sunshine from new germination occurring.  This tactic is also used by invasive species like the bastard cabbage (Rapistrum rugosum).  Given a plant has a deep and healthy root system, that rosette will “bush up” into a full plant when the average nighttime temperature reaches a certain level – for bluebonnets this seems to be somewhere above 50 to 60 degrees (F).

COMPETITION: The less the better

As mentioned above, plants use different tactics to survive, especially when it comes to outcompeting other species for the same area.  Some plants will use large flat overlapping rosettes to crowd out other plant seedlings, and some will actually disperse chemicals to retard the growth of other species (allelopathy). Still others try the parasitic approach to at least remain on equal terms by tapping into the roots of other plants to steal nutrients – the Texas paintbrush is one such plant.  The less competition in the area will ensure that a species has a chance to thrive.

That said, monocultures (where only one species thrives) are actually not good for the overall sustainability for a diverse Texas wildflower season. I know from watching website visits that most folks love to see acres and acres of solid bluebonnets. However, if that were the case everywhere in Texas then eventually the bluebonnet would be the only wildflower and even its future would be in jeopardy.  Having various fields that are monocultures of one species of wildflower is not bad and can actually increase diversity in and among species. What is bad is to have all fields one monoculture. Invasive species are so dangerous because they tend to create vast monocultures to the extinction of other species - they have not learned to play well. This extensive monoculture approach of invasive species can lead to a decline in a healthy population of pollinators.  Isn’t it interesting that biodiversity in nature is the key to the survival of individual species?

Winter Grass is the number one invasive enemy of our Texas bluebonnet species.  There are now several very invasive winter grasses that outcompete the bluebonnet germination and rosette development. Most of these winter grasses were actually developed to provide either winter grazing or for erosion control.  These winter grasses can respond quickly to the right conditions and create dense and widespread monocultures along our Texas roadsides – and they have!  These grass monocultures crowed out our spring wildflowers that are attempting to germinate and survive.  Native grasses tend not to arise during the early winter months, giving our native wildflowers the chance to establish themselves. When the native grass does awaken, it is later in the spring and there are specialized late spring native wildflowers that have learned how to compete with the tall native grasses.

Even the dead vegetation from the previous season can shade out germination and development of new germination.  The overcontrol of wild fires and urban development has resulted in acres and acres of built of dead, decaying vegetation.  Prescribed burns and even flash floods can help clear out that dead vegetation.

SOIL and TOPOGRAPHY: It has to drain well!

With a few exceptions, most of our Texas wildflowers prefer soils that drain well and a topography that allows water to seep down to provide a moist but not saturated soil.  If you have house plants, you know you have to provide just the right amount of water and in most case provide a way for the water to drain through the potting mixture. But you also know that the soil must be able to hold onto some water and not dry out too quickly. The soil must also be able to “breathe” in new nitrogen and other nutrients. So very loose soils like grainy sand or dense packed clays are not the best for wildflowers. For bluebonnets the soil has to be “alive” with Rhizobium bacteria that it uses in a symbiotic relationship to fix nitrogen in the soil into a usable nutrient form (this is typical of the legume family).

SUNSHINE: The energy of plants!

We know from our early school education that plants like sunshine.  The wildflowers that cover our landscapes in the spring love sunshine! Dark damp days can literally put an end to the hope of a colorful landscape filled with bluebonnets. I actually saw this happen one year when we went almost an entire March without a sunny day. However, lots of hot dry sunny days in February and March can result in an early and much shorter bloom. 

Conclusion

As you can see, it takes a combination of factors over many months to cook up a bountiful and colorful spring wildflower show.  The good news is that wildflowers do not bloom for our enjoyment, they bloom so their species will attract pollinators and then produce lots and lots of seed. That seed can remain dormant but viable in the soil for many years. They don’t really care about some short-term changes in climate, they are banking on the long-term investment in the survival of their species. They are willing and ready to adapt to any slow evolving change in climate – after all, they have been thriving on Planet Earth for over a 100 million years. They have learned how to deal with the short-term and long-term surprises in Mother Earth’s changing climate. 

References

Allelopathy - https://en.wikipedia.org/wiki/Allelopathy
Bastard Cabbage - https://www.texasinvasives.org/plant_...php?symbol=RARU
Damping off - https://en.wikipedia.org/wiki/Damping_off
How to Grow Native Wildflowers - http://www.seedsource.com/garden/planting.asp
How to Series - https://www.wildflower.org/learn/how-to
Ready! Set! Grow Wildflowers! page on this site.
Rosette -  https://en.wikipedia.org/wiki/Rosette_(botany))
Vernalization - https://en.wikipedia.org/wiki/Vernalization