permaculture

["Lawrence F. London, Jr." <venaurafarm@bellsouth.net>]

Canada Thistle
Cirsium arvense (Linnaeus 1753) Scopoli 1772 (Family Asteraceae)

http://www.agr.state.ne.us/division/bpi/nwp/canada.pdf
this link says that it can accumulate toxic levels of nitrates

http://www.commanster.eu/commanster/Plants/Flowers/SuFlowers/Cirsium.arvense.html

Maybe it could be used in a constructed wetland to catch nutrient-rich 
runoff from food producing gardens or compost piles and concentrate and 
store nitrogen for later harvest and conversion to nitrogen-rich compost 
for garden application and soil fertility building; used in tandem with 
leguminous cover crops.

I have heard that it is a host plant for important beneficial insects.

It is considered an invasive weed.
It is far less so that many other weeds (Bermuda grass

I am learning how to get rid of Bermuda in fallow fields by allowing 
natural plant succession, plants emerging from the soil weed seed bank, 
to outcompete it. In the field in question mustard, winter rye, fescue,
wild millet curly dock seem to be doing the job, also with eradicating
redroot pigweed in seedling stage during drought through shading and 
competition for space and water above and below ground.