It has been a long, long time since I have used one of the home soil test kits available in neighborhood gardening and grow shops.My thoughts are that they are OK but a bit overpriced for what the customer gets.
The home tests will give the gardener a general idea of what the macro nutrient levels are for the soil. That can help those who are starting a new garden and just want the basic info. It is kind of hard to believe that the pH test is going to be any more accurate than saying that the soil sample is acidic or alkaline (sometimes called sweet soil). When it comes to the pH there seems to be so much that has to be done exactly right before the test results can show any details. I don't want to go as far as saying the home kit pH test is worthless but I would be leery if I had to depend on it for changing the pH of my garden soil.
The tests that involved sending off a sample were much more detailed. We got back not only the NPK numbers but info on how much of various fertilizers to add to get the number up to where it should be. If the level was already higher than is considered optimum they included suggestions on how to reduce the levels. Bonus was the pricey test included results for some of the secondary and micro nutrients and just as important the results for percentages for both the organic material and the mineral base in the sample.
The few mail in tests I had done involved buying the envelopes and instructions from a local garden supply store so it was pre-pay. The results came back several weeks later. Those test were conducted by the County Co-Operative Extension Service. Each state in the US has a such a co-operative service and often they are part of the state's university that handles agriculture and animal research. Maybe do a search on the internet to find the address and phone number and contact the service directly to find out what is currently being covered by the state's test.
Plus each county should have an office for the Extension Service, usually in the county seat.
