Nothing improves your soil like compost, just my opinion. Check with your County Extension or your local landfill to see if they have a composting program. We have free compost available here, you just have to load and transport it yourself. It's excellent! Not a substitute for fertilizer, though. Very low analysis in fresh compost and it depletes quickly. The beauty of the compost is that the cellulose fibers act like little sponges and absorb moisture and nutrients until they break down themselves. They expand and contract as they are wet, then dry, leaving air pockets in the soil as well. All great for soil health and plant growth.
Anne, that Azomite is fine as far as it goes, but according to two nursery people I respect highly in Salt Lake (where I lived for 21 years) it's just trace elements, not really a fertilizer. The main useful component is the Silicon which is definitely gaining popularity for use on a variety of plants. Here's the chemical analysis from the MSDS sheet NaK2Ca5A13Si21O706H2O plus varying trace amounts of other minerals including silver and some toxic compounds. You gotta be careful of stuff that says it's 'natural' just because it comes straight out of the ground. Lots of toxic stuff comes straight out of the ground, including lovely things like arsenic. Unless they test each batch, they don't know what's going to be in it. They only have to test it if it's for human consumption.
I did some separate research on Silicon and am now supplementing my veggies, brugs and orchids with a product called Pro-Tekt 'The Silicon Solution'. It's so far shown good results with increasing tolerance to cold and also resistance to fungal diseases. The theory is that it helps to strengthen the cell walls.
