And Pretty Yellow Flowers

Here's another in the formerly obnoxious weeds of the garden category. Not a weed to everyone though. My gardening helper/expert has been planting them around trees and in my raised vegetable bed. When people would ask me why, and aren't those pods poisonous? I would say something ignorant like, I think they're some kind of companion plant. Every tree needs a friend. Or, people use the seeds to worm their horses or dogs.... I think.

Well, decided it was time to get more knowledgeable on the subject. I asked Sean how to spell Crotalaria, but he wasn't sure. Knew the common name was Sun Hemp though, so I had a Googleable name. What a marvelous thing the interweb is.

Crotalaria juncea
A tall East Indian shrub, Crotalaria juncea, known also as Sun Hemp, of the legume family, having slender branches and yellow flowers, and an inner bark that yields a hemplike fiber used for making ropes, sacking, etc.

Crotalaria juncea L. is a rapid growing crop that is used for fiber production in Indo-Pakistan. It is also good for use as a green manure in many tropical and subtropical areas in the world as an organic and nitrogen source. It suppresses weeds, slows soil erosion, and reduces root-knot nematode populations (Rotar and Joy, 1983). When plowed under at early bloom stage, nitrogen recovery is the highest. *Tropic Sun* sun hemp can produce 150 to 165 kg/ha of nitrogen and 7 t/ha air-dry organic matter at 60 days of growth under favorable conditions (Rotar and Joy, 1983). In southwestern Alabama, plants grown for 9 to 12 weeks produced 5.9 t/ha dry-matter and 126 kg N/ha (Reeves et al., 1996). Leaving these residues on the soil surface over the winter resulted in the release of 75 to 80 kg N/ha (Reeves et al., 1996). In the tropics, *Tropic Sun* grows and produces seed year round at elevation of 0 to 300 m, and in summer up to 600 m. In Guam and Puerto Rico, C. juncea is grown under conditions similar to Hawaii. In the continental United States, C. juncea is adapted to spring and summer planting in the South and Southwest (Rotar and Joy, 1983) and can be grown as a winter cover crop in Alabama (Reeves et al., 1996). It is suitable as a green manure crop as far north as Maryland, but may not seed well north of 30* latitude.

As with many other members of the genus, C. juncea contains pyrrolizidine alkaloids, which are converted into potent toxins in the liver. Highest alkaloid levels are found in the seeds. Toxicity varies from toxic to non-toxic among genotypes. Laboratory tests and feeding trials with the Hawaiian variety, 'Tropics Sun', suggest that both seeds and forage of are nontoxic. Stress conditions may also affect the degree of toxicity. To reduce chances of poisoning, it is best to limit C. juncea forage intake to no more than 45% in rations for sheep, 10% for cattle, and not fed at all to horses and pigs.

So, looks like it does quite a lot towards improving a garden. Suppresses weeds, produces nitrogen, and reduces nematode populations. Plus, not toxic to animals in moderate quantities. And, pretty yellow flowers too. I don't think you're supposed to smoke it though.
Whataya know, glad we checked into it. Now I won't sound so dumb when people ask.