Answer: One of the beauties of raised beds is that the soil is never compacted by being walked on. Try to loosen your "soil" as much as possible before making the raised bed on top of it. It will help with drainage. Top soil will work just fine and is usually cheaper than potting soil. Add plenty of compost and mix it in with the soil. Since this is the first season, I'd mix about 1/3 compost in with your soil.
Compost improves drainage in clay soil, improves moisture retention in sandy soil, adds nutrients, and improves the workability of any soil. Manure is good also, if it is well-aged, at least 6 months. Otherwise, add it, but don't plant for a season while it decomposes and loses its "heat." Before each season's planting thoroughly incorporate several inches of compost. It's the best thing you can do to improve your soil! Mix a balanced fertilizer (e.g., 10-10-10) into the soil. Organic fertilizers are also good, but they're often harder to find in a balanced ratio, so you need to use several to get the nutrients. Fish emulsion provides nitrogen, bone meal provides phosphorous and seawood/kelp or greensand provides potassium. Follow package instructions for applying fertilizer.
After planting, put a layer of mulch on top of the soil. Mulch is great to help retain soil moisture, reduce weeds, and as it breaks down it provides nutrients to the soil. Any organic matter can be used as mulch. Try compost, bark, wood chips, straw, or pine needles. Best of luck with your raised bed!
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