While normal cold composting, using a one year cycle, will not kill the roots of perennial weeds composting in a covered heap, from which the light is excluded, for a period of two years has been reported as being effective
for many perennial weeds. When I took on my first allotment plot it was covered in perennial weeds and I took the lazy approach of making a pallet bin using four pallets, filling it with weeds and leaving it until the pallets rotted. Although there were
a few roots struggling to survive on the surface where some light had seeped in, the compost was excellent. When using this and any other method of treatment on this page it is recommended to check the compost at the end of the treatment to ensure the absence
of living roots before use.
ASK Organic (http://askorganic.co.uk/composting/perennial%20weeds.pdf) recommend using a separate plastic compost
bin so as to ensure that all light is excluded which may not be possible if using a wooden bin. The material is kept covered in the bin for two complete years to rot down.