Your potting soil may not be mixed correctly. Make sure it has peat moss or something similar to hold moisture. It may need something like vermiculite to make it soft enough for the roots to spread out in. If you are going to mix in manure you will need to add both these to make a great soil. They are not required but make it easier for you to mantain a mosture level and help your plants thrive.

Additionally you may want to mix several different types of manure and soil together. You know the saying you are what you eat, same goes with plants. if they dine on one type of plant they only get that type of nutrient. When cattle are feed just one or two types of feed the manure does not have that great of mineral content. The farmer may change the feed evry several days but you still only get a small portion of what you may need. I just mixed my soil today and used 7 different types of manure and soil, from three stores.

I would recomend the 2006 edition of 'Square Foot Gardening' available at libraries and bookstores everywhere.

You can make a raised bed and fill it with whatever. There is more to the method than that. You will get a lot of clearly explained ideas in the book that you can consider and very clear instructions on how to do everything.