Answer: You will want to till it in several weeks before planting, so your timing will depend on the weather conditions allowing you to get in and work your soil. It is a good idea to mow it before tilling, precisely for the reason you suggested. It will not be much of a protection against wind; if wind is a problem in your garden you might consider a more substantial windbreak of perhaps a fence or other larger plants such as shrubs or evergreen trees. You might also use a heavier mulch to help keep the soil in place.
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