If you are in waterloo, just pick up the bags of clippings that your neighbors put in the trash, specially dead leaves in the fall. These will give you a mellow, non-smelly compost that you can use with just about any veggie. In it, you can mix other, stronger organic compounds for fertilization purposes. Your local Starbucks will give you all the coffee grounds you want (low pH, high N). If you have a friend who has a wood stove, a few pounds of wood ash will give you all the K you may need (high K, high pH, high micronutrient). some bonemeal will provide some P.
In practice with clay you need texture (soil breakdown) more than fertilization, and for that straight leaves, used as mulch to allow prolonged action by an army of worms, are the best. You should simply lay them uncomposted, bag after bag, on your garden and plant through them. nature will do the rest. They will also disappear within the season, composted by the worms, so that next year you can direct seed in the resulting finer soil.