Answer: Generally speaking it is a good idea to feed your soil regularly by adding organic matter to it. Organic mulch, as it decays, is a nice way to do this, as is topdressing with compost. (You will be surprised next spring to find how that layer of mulch has "disappeared"!)
In my garden at home I generally maintain a steady level of two or three inches opf mulch on the flower beds, and use a nice layer of straw on my vegetable garden. It can be turned under (many gardeners do this, especially in the veggie garden) or left in place for the earth worms to circualte through the soil. This is a matter of personal preference. You will find much of gardening ends up to be that way.
However, especially with a new garden, it is really important to perform some basic soil tests so that you know how your soil is now and can determine the best amendments to add to it based on the results and what it is you are trying to grow. Your County Extension can help you with both the tests and interpreting the results. Their number in Philadelphia is 560-4150.
Enjoy your garden!
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