I don't use chem. fertilizer on my garlic and have very good results. I mix in rotted cow manure compost with my soil before planting and after planting, I cover with about 4 inches of chicken litter which includes shavings and manure from cleaning the chicken house over the year. About every 2 weeks while they are growing I use liquid fish and seaweed fertilizer as a foliar spray. This works for me and I get great garlic. The key is to start with the best seed garlic that you can get. I guess that if you use 10-10-10 or something like that you would need to get a soil analysis to know for sure how much to use.

Several places suggest 3-4lb of 10-10-10 per 100 square feet at planting.

I prefer to till in manure before planting because it improves the drainage, aeration and moisture retention characteristics of the soil. Take advantage of the empty bed and improve the soil! Once things are growing there, you can fall back to soluble fertilizers.