I am wondering if it is possible to mulch with some tall tropical grasses that have gone to seed. They are abundant on the site I am helping with and the main potential source of mulch for the time being. The site is in Mauritius, which is humid wet/dry tropics - but has around 23 microclimates, and I have yet to figure how to exactly define it Would it be enough to kill the seeds by submerging cut grasses in water for a few days? Any other thoughts or opinions?
very unlikely a few days will do it. can you cut the seedheads off before you chop the grass? i do that here for some of the bigger grasses and it isn't too much work in comparison to weeding them out later. if you have chickens or other animals to feed they would likely eat the seeds... you'd have to make sure they weren't toxic first, but i doubt that is likely. otherwise, you can bury them deeply, ferment them, burn them, etc. to keep them from being a problem. biochar... etc.
I don’t worry about seeds in the mulch material I use but then I’m in a temperate climate, not tropical where things grow rapidly. If it’s feasible, do as songbird suggested and cut the seed heads off. Put these in water if stock won’t or shouldn’t eat them but leave them in the water for a couple of months. It’ll stink but the seeds should rot. Good luck with it.
good advice so far; a soak seems to go best if you really let it go anaerobic; make sure you've got some green leaves in the barrel, too. and stir it once in a while. My favorite is a deep-mulch chicken yard with birds that are used to foraging.