have 3 in ground, bush form, that i protected last night from the impending ~-10F temps. did them all slightly different:
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pruned back and pinned down, covered with a mound of mulch, bucket on top, mulch around the outside rim of bucket.
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pruned back and pinned down, covered with mulch, two layers of cardboard, and then covered with more mulch. currently has an extra bag laying on top of that as well.
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pruned back and not pinned back, covered with a mound of mulch, bucket on top, and mulch around the outside rim of bucket.
i wasnt planning on putting mulch around the rim or adding the bag on top of #2 but i bough extra 
one could probably get away with putting a layer of mulch in and then just topping it with a full, unopened, bag that you can open and disperse the next spring. well see. i only added one temp sensor to the top of the pile of the mulch in the bucket on the left:
