One way to know if a site is relatively warm (has a longer growing season with fewer killing frosts) is to look for land in mid-fall when you can compare how far along native trees are towards dormancy. Best fruit growing areas are often known in the East and will already have established orchards. People have been growing fruit here for 300 years but you might luck out, I guess, and discover your own tiny "banana belt". As far as productivity- of course you will be able to grow a wider range of varieties in a 6 than a 5 and some would yield more with a longer season- at least over time. But your question really seems to be can you find a Z6 in regions that are predominantly 5. I think it's the leeward (southeast) side of large bodies of water that have moderated temps as in far upstate NY, not far from Buffalo and areas like Lake Geneva. Also along rivers such as the Hudson Valley and running up the Housatonic in CT. Some of the fruit you listed, like cold-hardy figs and Jap persimmons aren't going to work for you, even in a Z6 without protection.

rtg: Your description of the leaf problem does not exactly match that of fireblight, but it could be. FB usually blackens the leaves more than browning them, and the leaves droop rather than curl. So you could also have something like an aphid or mite problem (Have you looked under the leaves?) or too little/too much moisture. It might be worthwhile to Google "fireblight" to see if you can find photos that match your problem. If not, you will have to take a closer look for aphids and mites. When problems like this occur on old or new growth, the best thing to do is usually to prune it off. Please state your location when asking a question of this nature. It makes it easier for the diagnostician. It's already hard enough to make these guesses from long-distance. Don Yellman, Great Falls, VA

1. Yes, apples require four seasons and will not do well if kept warm all the time. In Zone 7 you will not risk freezing out the roots even with a container grown plant. 2. Much depends on the rootstock, but you can probably do OK with the larger pot size as long as you don't overwater and have a reasonably moisture-tolerant rootstock. 3. I am not an expert on potted trees but would think that with a 20 gallon pot you could grow a fully dwarf apple tree for many years without having to root prune. Get something on M.27, EMLA.27, P.2, P.22, or Geneva 65 roots and it will do fine. It may take some searching to find a place that has these. If you know how to graft apples yourself you can just get rootstocks and graft your favorite apple on top, which might be easier.

I would guess and hope that your trees will be alright and will probably grow more next year. I don't think covering the graft unions is hurting anything right now, although in the long term I do think you'll want to uncover the graft unions to prevent the trees from growing too large. If the grafts are covered with soil, the wood above the grafts may take root and you'll essentially have 100% height seedlings instead of whatever rootstock you actually intended to have. What I might consider doing is moving back a lot of the soil from around the base of the tree to uncover the graft union, and then fill this up with a little gravel immediately adjacent to the trunk to allow drainage, and cover the rest (a circle of perhaps 2-3 feet radius) with wood-chip mulch. So then you'll have drainage to keep the graft union dry and prevent rooting of the scion, while providing a beneficial weed-free zone over the young roots. How does that sound?