Answer: The smaller the pieces of organic matter, the faster they will decompose, so shredding them is always useful. It's a good idea to have organic matter as decomposed as possible before adding it to the garden beds, but if you aren't actively turning the pile to introduce oxygen, it probably won't decompose much more over winter. So you can till it in now or spring, whichever suits you. It's good to let soil sit for 2-3 weeks before planting, if possible, after adding lots of organic matter.
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