please be careful with bioassaying that. Phragmites sp may have gramine and other unwanted alkaloids. According to the Merck Index, gramine is not soluble in pet ether ( = naphtha), so pulling with naphtha and/or recrystallizing the final product later with naphtha can help getting rid of it (but this is still not guaranteed, please start with very low doses when bioassaying).
I dont know whether dmt is present in these plants as the normal compound or as dmt n-oxide (due to being green leaf, therefore plenty of oxygen). In that case, naphtha might not pull the wanted alks either. So if you dont have good yields pulling straight with naphtha, try again pulling with something like limonene/xylene, and salting those solvents out, maybe making the zinc oxide reduction, re-adding base, re-pulling with naphtha.
I think extracting with a solvent like limo/xylene and the salting out with FASI/FASA (and later re-converting to freebase) might be good also to get rid of plant oils/chlorophyl/impurities without the need for defating.
btw when I say naphtha I mean any of the more or less equivalent non-polar aliphatic solvents (naphtha, hexane, heptane, etc)
good luck and post back the results if you do extract and/or bioassay. Just once again, please be careful!