Reddit reviews Propagating Plants: How to Create New Plants for Free

To add to Guygan's response - I really like this book.

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To answer your question - hardwood cutting is a fall/winter technique where you take woody material, let it callous, and then let it wake up and root in the spring. Softwood or semihard is a spring/early summer technique where you take fresh growth that is beginning to become ligneous and root that. You generally want your cutting to be not the super soft new growth at the tip, but the firmer stuff down below. Remember wood is a carbohydrate that the plant can use in an emergency situation, so a slightly woody but still growing cutting is going to give you your best chance because the wood feeds while the growing hormones are still pumping.