I used untreated wood. Didn’t paint it or stain it.
Think it might be the heat. Had beautiful plants, just no fruit. I used Mel’s mix so I didn’t understand about phosphorous, other fertilizer. Wasn’t needed according to the book.
Now that it is cooler, going to try again this weekend. What would be good for the fall?
Almost all root crops with maturity date of 45 - 90 days: carrots , radishes, turnips , rutabagas,kohlrabi ,onions , garlic .
Also , leafey greens like swiss chard ,lettuce ,radicchio & chickory, endive & escarole, quick growing okra, peas , maybe some tomatillo.
Since you already have a wooden frame for your 'grow box', consider adding an angled lid of glass or plastic for a "cold frame".
A "cold frame" will retain heat and extend your fall harvest ; in the springtime , it will give you a jump on the planting season.
In much northern zones, the addition of a "Hot manure" under the top soil of a cold frame(ie.:fresh horse, fresh chicken)
will generate enough 'bottom heat' over the winter for more sensative plants surviving the winter cold under glass/plastic . At least , consider it .. as a 'poormans greenhouse'.
***Now that it is cooler, going to try again this weekend. What would be good for the fall?***
http://www.fanicknursery.com/Downloads/CalendarCurrent.pdf