War on Weeds: Henbit

Henbit

Henbit is an annual cool-season weed.  It's the weed that around here in the spring turns lawns purple with their tiny flowers. Its nectar and pollen are useful to bees.

Henbit prefers cool, moist soil, so it flourishes in the spring.  It usually grows to about 6 inches tall. Its seeds germinate in the fall, live through the winter, and then grow and flower in the spring.  As temperatures start to rise, it dies, leaves lots of seeds for fall.  Henbit spreads primarily by seed, though the stems can root where they touch the soil.


Weeds invade where ever the grass grows thin.  A nice thick lawn will help fend off henbit and other weeds.  Mow your lawn regularly at a high setting, ideally about 2 1/2 to 3 inches, to discourage weeds.

The first line of defense against henbit is a pre-emergent herbicide such as Preen or corn gluten. Then when the seeds start to grow, they'll only get as far as germinating, but when they can't take root, they'll die.  Henbit seeds germinate as fall rains begin and the nights begin to cool off.  Around here, that means in September.  So to control henbit with the pre-emergent herbicides, you need to apply it before this point in the season.

Henbit in dormant lawn

Henbit has a shallow root system, and can be easily hand-pulled from moist soil.  In garden beds, use mulch to prevent weeds.  A 2-3 inch thick layer will block sunlight from any weed seeds on top of the soil.  It will also conserve moisture.

I have been applying corn gluten to my lawn the last several years as an organic pre-emergent weed control, but have continued to have weeds such as henbit growing in my lawn.  So I started reading up on these weeds.  As I began to understand the life cycle of henbit, I saw my problem right away.  I had been applying the corn gluten twice as year, as instructed, but at the wrong times.  It said to apply in the fall, and I had; in October.  That would be too late to control henbit, which probably has already germinated by then.  This year I plan to apply the corn gluten earlier; in late August or very early September.  I am pleased to see that organic means should be sufficient to control this weed, without resorting to more toxic products.  It will be very interesting next spring to see if I can tell any effects on henbit growing in the lawn.