We have had an extended autumn, which has given us a longer window to sow bluebonnet and other wildflower seeds. Ideally, seeds would have already been in the ground; they can still be sown—but get them in the ground as soon as possible.
Most wildflowers, bluebonnets included, have hard seed coats that are impervious to water uptake. Without certain mechanical and/or environmental treatments, seeds fail to germinate.
Cold and moist are the common environmental factors required for germination. Many wildflower seeds have a cold requirement and unless seed is exposed to conditions of moist, cold during winter months seeds can remain dormant for many seasons. The cold, moist treatment also serves to break down the seed coat as moisture freezes, then thaws, then refreezes, a process which over time will break the hard seed coat.
Two treatments horticulturists use to satisfy and overcome the dormancy conditions are scarification and stratification.
Scarification: used for species with hard seed coats. Seed coat is mechanically altered by rubbing with sandpaper, nicking with a file, or softening the seed coat by covering seed with hot water or sulfuric acid. Be aware that fragile embryos can be damaged with this process.
Stratification: the process in which imbibed but dormant seed are exposed to a period of chilling (33 to 50° F). Seeds are placed in stratified layers of moist sand or soil. This process is also known as “moist chilling.” Seeds must be planted early enough in the fall to allow them to become completely imbibed with water in order to experience the complete benefit of the chilling period.
Texas bluebonnet, Lupinus texensis, the state flower of Texas, is a legume in the pea family with a hard seed coat. Seed of bluebonnets is sown in autumn to allow sufficient time for the natural processes of scarification and stratification to be initiated. Freeze/thaw cycles that occur during the winter months will, over time, break down hard seed coats. Some bluebonnet seed may germinate following the first winter, while other seed may need several years for seed coats to break down sufficiently to germinate. Bluebonnets grow well in USDA hardiness zones 6 and 7, and in alkaline, well-drained, low-fertility soils in full sun. After sowing seed keep soil moist but not saturated.
A Texas source for bluebonnet and other wildflower seeds is Wildseed Farms in Fredericksburg (wildseedfarms. com).
Ellen Peffley Harp, a retired professor of horticulture at Texas Tech University, writes about gardening for several Texas newspapers.
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