There have been several posts here where people describe the problem with planting seedling trees and shrubs into the garden - they tend to get lost, and are never seen again. Over the years, I've used a nursery bed for small woody plants, actually part of my vegetable garden. The problem with that approach is that I no longer have much of a vegetable garden, it's full of adolescent willow oaks, hydrangeas, etc.

If you have a good track record overwintering things in pots, and if your seedling is in a large enough pot, you could sink the pot, or plant it (pot and all) in a mulch pile. Personally, I have no luck with this approach and have to get all my plants into the ground before winter - I have trouble getting the right amount of water into the pot without drowning the plant or letting it get too dry.

Maybe a compromise would be to stake out a nursery bed that's small enough that nothing could be left there beyond the time when it's ready to be planted out - a raised bed could work well for this.

That is what I am most afraid of...planting it and then thinking it is a weed somewhere down the road. If I do a raised bed, how big should it be? I know they are supposed to be very fast growers.

You'd just need to figure how big you'd want it to be when you move it to its permanent location, and then make the bed large enough to hold that sized tree.

Personally, I'd be comfy planting out about a 5' tree, and for that I'd want a bed about 3' across. You'd want to mulch heavily, but keep the material away from the trunk. Raised beds can dry out really fast, and I'd assume, from the name, that these guys like a fair amount of moisture in the soil.

The idea of the raised bed seems really good, because it essentially ensures a compact root ball - and you'll know just where the roots are. You might ask this on the trees forum, though - those guys are great and really know their stuff.

Good luck!