If you collected a soil sample (a few spoons of dirt from 5-8 places in your garden, put in s plastic baggie.) Then get it tested - ask for a 32 element ICP. I

If you collected a soil sample (a few spoons of dirt from 5-8 places in your garden, put in s plastic baggie.) Then get it tested - ask for a 32 element ICP. It's fairly cheap, 10-20$USD, gives you a run down of those 32 elements, and then you can see if there are any anomalies. They give you an answer in ppm (parts per million.) For example. Then you look at the published standards for soil quality. For example in your case, residential criteria. In your state. Find online. If you are more than a factor of 10 or 100 above that, in one element, you may have an issue. If there was a fire, and ashes blew your way, there could be detectable amounts. If there are, especially if those elements are suspected to originate from the fire. You can worry about further tests. Some organic compounds- by products of the fire may be there, and be measurable. And that gets more expensive.(~ $500) But you'll probably find everything is ok.