The bluebonnet is a member of the genus Lupinus in the legume or pea family. Like most legume seed, it has a very hard seed coat which will break down over time by decay from bacteria and other microscopic organisms, abrasion or a freeze/thaw. It may take several years for some seed coats to deteriorate enough to germinate, while others will germinate the first year. This staggering insures that some seeds will survive from one year to the next because seeds are protected from the environment as long as they remain dormant and do not germinate.
While this hard seed coat is a necessary natural protection, it may be overcome by scarifying the seed. Scarification means scratching or nicking the seed coat. One important thing to remember - by scarifying you are increasing the number of germinated seeds which are vulnerable to extreme weather conditions. Once scarified, most seed will germinate quickly and the seedling will require water. You must be able to water if you are going to scarify the seed. Bluebonnets are fall-germinating annuals that must have fall, winter and spring rainfall to ensure that the seedling will survive until spring flowering and seed set.
The Lady Bird Johnson Wildflower Center does not recommend scarifying bluebonnet seeds which are to be planted outside in a setting that will not have irrigation during the winter and early spring. There is also a risk that scarification may damage some seeds, consequently, the number of seedlings actually available to grow and flower may not be significantly increased. Even if scarification does increase the number of seeds germinate, this does not insure a healthy, self-seeding community of bluebonnets because there are many factors which influence the growth and flowering of bluebonnets after they have germinated. The best goal is not a high initial rate of germination, but a productive stand of flowering bluebonnets self-perpetuating from year to year.