Hi Marcy,
Sounds like a really interesting project. It will take a thorough comparison to prove the benefits to those who doubt. I am sorry I assumed you are in the UK.
I guess the best veg for trialling would be those you eat a lot of. One thing I have found is that an excess of things like cabbage and cauliflower means that they often do not get eaten, so I would concentrate on those things which store well such as potatoes, carrots, parsnips and beetroot. I would try some leaf veg as well just to see the difference as those mentioned before are all root crops.
How much rain did you get during June, July and August this year?
BR
Neil
