I didn't think that this was a unique idea, but a lot of people are loving it and asking questions so I thought I'd share
This is an example of one of my finished containers:
Recognizing that I had a TON of nursery pots just laying around, here's what I did:
1. Find a nursery pot that's only slightly smaller than the decorative container.
2. Find a nursery pot that fits snugly into the first nursery pot. Bonus points if you have a lot of these!
3. Take random rocks and build up the height of the decorative container so that, when you sit the larger nursery pot inside of it, the lip of the nursery pot is flush or slightly lower than the lip of the decorative pot.
4. Leave the nursery pot in place, and pack drainage rock around the sides. The goal is for the rock to hold the nursery pot in the middle of the decorative pot. You can place pretty rocks on the top if you want (like I did in the pic), but drainage rock looks good by itself so it's really not necessary.
5. Fill the smaller nursery pot with the plants you like.
6. Sit the smaller nursery pot inside of the larger one.
This is how the decorative pot looks before I put the one with plants inside:
And here's how the internal pot looks after it's planted, but before I sit it inside of the decorative pot:
Now I have several nursery pots of that last one's size either in the greenhouse or in the hidden part of my gardens. One pot has Asiatic lilies, another has tulips, another has dahlias, another has asters, and so on.
The tulips will start to come up when this Winter pot looks scraggly, so I just take this pot out and slide the tulip pot in. When the tulips die back, I'll take that pot out and slide another one in. It'll take about 2 minutes, I'll always have something pretty going on in the container, and I just hide the others away until next year!
I haven't done this next part yet, but in theory you could pack the sides with container soil instead of drainage rock and then plant ivy, asparagus fern, or something similar in there. That would let the spiller hang down the sides year round, but the roots wouldn't prevent you from swapping out the pots at will.