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A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Wednesday - September 22, 2010

From: Austin, TX
Region: Southwest
Topic: Invasive Plants
Title: Fighting Sandburs with Bluebonnets in Austin, Planting Bluebonnets in Caliche soil
Answered by: Mike Tomme and Barbara Medford

QUESTION:

Mr. Smarty Plants, In my continuing fight against sandspurs I've decided that if I plant a copious amount of bluebonnets seeds that the foliage will choke out the sandspurs because bluebonnets set foliage in the late fall and early winter and will choke out any sandspur seedlings before they can take hold in the spring. Is my logic super flawed? What is the likelihood that bluebonnet seeds planted in September will flower in March when planted in caliche soil?

ANSWER:

Mr. Smarty Plants would never tell you that your logic is flawed. However, Mr. Smarty Plants doesn't think your idea will work. Sandburs (aka sandspurs, grassburs and a bunch of unprintable names) are just too tough. A little bit of shade and crowding won't stop them. They'll just grow right up through the bluebonnets and the two will thrive together. Think of the fields of bluebonnets you've seen and how, late in spring when the bluebonnets fade, the grasses come right back. Sandburs are a grass and they will do the same.

The sandbur you have is most likely Cenchrus spinifex (Coastal sandbur). This plant grows throughout the southern United States and Mexico. It favors poor soils, like caliche, and does well in recently disturbed areas. 

Control of sandburs is is most reliably achieved by hand pulling and, in the longer run, by improving the soil by adding organic matter and eliminating compaction. For hand pulling, learn to recognize sandburs when they have not yet produced the burs, or seeds, so you can pull them out as the opportunity arises. Here is a site that has more information about control of sandburs.

As for your question about planting bluebonnets (Lupinus texensis), early October is the best time to plant seeds. Bluebonnets do well in caliche soils. Here is a how-to article on growing bluebonnets.


Cenchrus spinifex

 

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