For me, plant selection is a fairly extensive process. I make countless google searches, sketch out possible combinations, and check every one of my gardening books for reference to said plant and its habits while considering it for my garden. I also determine at least two places where it might work both logistically and aesthetically before I plunk down cold hard cash for it.
When I do buy, I look for the smallest pot size offered--unless the perennial is a notoriously slow grower, like hakonechloa--because I find that the younger plants establish more quickly and easily. They also often catch up to their pricier, larger counterparts in a season or two... and frankly, I feel like I ought to be able to wait that long for a plant to come into its own. (I really must exercise patience if I want to earn the right to be thought of as a gardener someday!)
Once I have a plant, I often find myself moving it around a few times to find the "perfect" place for it. As an example, check out the small carex buchannii in the center of this picture. It will (I hope) look great surrounded by golden sage, golden oregano, coral bells, asclepias tuberosa, digitalis parviflora and a few annuals when they all grow up... but this spot wasn't even on the radar as a possibility when I bought it!
In light of my penchant for moving plants, I decided that this year I would treat my spring Bluestone Perennials order a little differently. I would work the plants into container combinations, observe them over the summer, and then plant them out in the fall--all in the hopes that I would plant them in the right place to begin with, saving myself the work of moving them again next spring.
Sounds like a perfect plan, right? Well... sort of. On the bright side, I was able to concentrate on planting the veggie garden and various winter sown annuals without tripping over the small Bluestone plants--or, worse, forgetting to water them. I had plenty of time to watch them grow and think about where exactly I should try them first in the garden, as the placement of the brownish red sedge shows.
However, I did also learn a lesson: Conventional container-planting wisdom (planting so that the container looks full from day one) just doesn't help small perennials get off to a good start. If you crowd them too much, they will not grow like they would given more room to spread out. Comparing the one alchemilla mollis that I planted in the ground with the two that were tossed into containers definitely proves that point.
So maybe the answer next year is just to pot any small perennials up into one of the numerous 8- or 10-inch terracotta pots that I have, and cluster them around my larger containers. Once the perennials start to fill those pots and need to be planted out, the frenzy of spring planting should be over, and they would look okay in the meantime.
Any other ideas on how to address this issue, other than A) making a holding bed, or B) having a space prepared well in advance of the plant's arrival? Frankly my .11 acre lot completely eliminates A as an option... and although the first paragraph may make me sound ultra-organized and analytical I really am too right-brained for option B!