The first contributor is compaction of the soil and moisture. Moss takes advantage of both. You can just rake it up but then I would suggest that you till your soil.
From the photo is appears you have compaction. If that is so tilling in a goodly amount of compost will help with drainage and aeration as well as adding organic matter and natural fertilizer. Acidic soil also tends to be more receptive to moss but the majority of Anoka County is sand plain and that is neutral. Shade also is a contributor to moss. I would guess your garden is in full sun so that shouldn't be the problem. I am giving you a couple links. One discusses moss in lawns but you may find additional information to help you. The second one is a link to our Soil Testing Laboratory. It would be worth while to test your soil before adding anything.http://www3.extension.umn.edu/local/article/moss-your-lawn http://soiltest.cfans.umn.edu/