I was piddling around on the Portland Nursery website the other night and noticed a brochure they had produced called "Edible Plants in Containers." I wasn't expecting much more than tomatoes or cucumbers, but much to my surprise... I found trees!
One in particular that struck my fancy included a dwarf apple, a lowbush blueberry, and strawberries. To me, that was screaming of forest garden. Any time you get fruit trees and berry bushes in close proximity you're halfway there.
All they were using was a half wine barrel, which means a person could theoretical grow a "mini forest garden" and take it with them when they moved.
The only downside is that it requires more maintenance. The soil will dry out more quickly, so you'll have to water more than you would a forest garden planted in the ground. And, trees in containers can become root bound, so at least every few years, if not every year, you'd have to take everything out and prune the roots.
The first consideration would have to be what kind of fruit tree you grow. Here's what Mid City Nursery says on the subject:
Not all fruit trees will grow well in containers for long periods of time. If you want to grow a fruit tree in a container for just a couple of years, then you can grow just about any fruit tree. However, if you want to grow a fruit tree in a container for its entire life, then you may want to try some of the fruit trees listed below. The size of container plays a factor in what you can or can't grow. Generally, you will want to use a container that measures 18 - 24 inches wide and about the same depth. Larger containers can be used as well. Wine barrels cut in half are often used. It really doesn't matter the material of the container as long as there is adequate drainage. Some of the fruit trees that can be grown well in containers are dwarf meyer lemons, dwarf kumquats, dwarf eureka lemons(will require regular pruning), genetic dwarf nectarines, genetic dwarf peaches, and some of the dwarf apples(varieties on the Mark and M-27 rootstocks only grow 8-10 feet). Also, pineapple guavas, chilean guavas, or strawberry guavas can be grown successfully in containers. Other dwarf citrus may do okay in large containers with regular pruning.I'd probably go with a dwarf pear or plum, if an appropriate variety exists. Or I might get adventurous and try jujube, or stick with plain ol' figs. Then some sort of low growing bush berry. Perhaps cranberries, or the lowbush blueberries mentioned in the brochure. Dewberries also sound good, but I wouldn't want to deal with thorns if I had to pull everything out of the container every year or so. Other interesting things to try would be ostrich fern, with it's asparagus like (or so I've been told) fiddleheads, or some sort of wild green. Trying to vine something up the tree would also be fun, although this trees are small and can't support much. You could try a smaller vine like cinnamon vine (a.k.a. chinese yam) as it stays relatively small (although, I don't know how easy harvesting the tubers would be). Or you could try something bigger like akebia or passionflower and just prune it heavily. Trees can be expensive, so you'd have to decide if that's a gamble you're willing to take.
In any case, it's an interest idea. One could also potentially start "sections of forest garden" and once they were established, plant them out into the actual garden area. It would be like buy potted trees or other plants, but it this case, you'd be buying whole sections of food forest. In this case, you might be able to get away with growing a bigger tree, so long as it's not staying in the container for too long.
