permaculture

[Toby Hemenway <hemenway@jeffnet.org>]

Lisa wrote:
> 
> A couple of years ago I got some tagasaste and autumn olive seeds,

A neighbor planted a bunch of tagasaste near me (Roseburg OR) and they have
survived and do not appear to have spread in 15 years. I concur with Rain;
Russian olive can be a problem but so far I hear no reports of autumn olive
being invasive.  

> We also have honey locust; what's the last work, is it nitrogen fixing
> or not? 

My fat book "The Leguminosae" (O.N. Allen) says early nodulation studies on
Gleditsia (honey locust; not Robinia, black locust) showed that no bacteria
were able to penetrate the root walls, which is the criterion for whether a
plant is called N-fixing (the bacteria have to be able to inject N into the
plant for it to be called a symbiosis). Some later studies showed that
occasional root swellings may contain rhizobia (N-fixing bacteria) but there
is not a significant amount of nitrogen fixed. Honey locust secretes
compounds that inhibits bacteria from nodulating, so altho occasional
nodules form, they never amount to much. Conclusion: you can't call them
absolutely non N-fixing, but they won't fix nitrogen enough to be of use.

Toby
www.patternliteracy.com