Our bluebonnets have finally gone to seed. They hung on for much longer than most others we’d seen. That may be due to their late transplanting. What was so beautiful became intolerably scraggly the last week of May, so time to say so long!

Image: bluebonnet patch with brown leaves and burst seed pods.

After bees pollinate the flowers, each blossom turns into a seed pod that look very much like peas or beans. After all, bluebonnets are lupines, which are part of the legume family. Legume roots are known for fixing nitrogen in the soil, so my plan was to trim off the plants and leave the roots to do their magic. Many seed pods had already popped open. Seeds were scattered throughout the garden, starting next year’s bluebonnet crop.

What is Nitrogen Fixing?

It would have been much easier to just pull the plants out. But I was determined to leave the roots in the ground. How exactly does nitrogen fixing work? Here’s what I learned:

When a legume plant dies in the field, all of its remaining nitrogen is released back into the soil. Nitrogen lives in the amino acids inside the remaining plant parts. In the soil, the amino acids are converted to nitrate (NO3). This makes the nitrogen available to other plants, thereby serving as fertilizer for future crops.[12][13] Legumes are sometimes referred to as “green manure“.

In many traditional and organic farming practices, crop rotation involving legumes is common. By alternating between legumes and non-legumes, the field usually receives a sufficient amount of nitrogenous compounds to produce a good result.

Another method of using legumes as “green manure” is to alternate rows of crops in one season. Farmers may plant two rows of non-legumes alternating with one row of a legume.

Adapted from https://en.wikipedia.org/wiki/Legume
Image: graphic showing the cycle by which nitrogen in the atmosphere is used and created by certain plants such as legumes.
The EPA published this illustration of the nitrogen cycle many years ago. It shows the role of nitrogen-fixing plants such as legumes, including our friendly bluebonnets.

So not only do bluebonnets add beauty to the yard — bluebonnets gone to seed contribute to the health of our soil. We can certainly use it, considering the poor quality of the top soil the builders put in the yard. Next up: summer annuals!

Leave a Comment

Your email address will not be published.

Scroll to Top