By Caballero1967 (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons
Blackberries enter the composting chain when we are clearing an overgrown site to make a garden or when pruning a plant grown for fruit. This may sometimes involve cutting unwanted leafy green canes or removing the year-old canes after fruiting. These
shoots are cut down to the base presenting the composter with a lengthy shoot which it is better to prune after fruiting as if left until the next year these will die and become hard and brown making them more difficult to handle. Normally when
removing these I would suggest cutting them into 2-3 foot lengths for ease of handling.
Bramble roots sprout from below the ground so when trying to remove bramble roots to clear ground it is necessary to pull up the crown,
which may have fresh shoots growing from it, I personally would not cold compost this part of the plant preferring to add it to the “council” green waste bin. However it has been reported that the plant does not regrow from the compost
once it has been shredded so it might be worth giving it a try.
Shredding the bramble avoids the scratches and effort involved in cutting it into short pieces. It will also speed the composting process and reduce the number of whole
thorns in the bin. This is quite important as old thorns take a long time to compost and any remaining in the immature compost are bound to find your fingers.
There are two techniques used for shredding brambles. The first involves cutting them
into easily handled lengths of about 2-3 ft that can be easily fed into the shredder. The second technique, which I have not tried, involves feeding the whole length of the bramble into the shredder root end first. The self-feed action should pull
the whole length of bramble through the cutter.
Whichever method is used the result is the same 1-2cm bramble chips which can be added to slow the compost heap for a year after which it can be added to the normal compost bin