All the mints are agressive. If you want to have it in the ground use a root barrier and then some kind of edging that will help you to keep the runners in place as well. I will say that my pineapple mint isn't as vigorous as the spearamint. But then I'm in
zone 7 working with clay soil. Your conditions are probably very very different.
Peonies actually like cooler climates than mine but I still have 5 in my garden and would happily make room for many many more. They can take a long time to establish themselves (around 3 years in the average) But they live around 75 to 100 years and increase the size of their clump every year. The
flowers don't bloom for very long a week or two at best but they make the greatest cut
flowers. Second only to
roses in my opinion. So if you have a protected (from the wind) sunny place about 3 foot square I would definitely
plant one. They come in a variety of Whites, Pinks, Reds, a few purples and even some oranges.
I would also have a mock orange if you have any type of arbor or tall fence that it can rest on. They grow from canes and I like them more upright so I like to see them supported. But if you like the weeping
willow type shape you can just give them lots and lots of room because the canes do get quite tall. The smell is outstanding and I like them in cut
flower arrangements.
I love my crocuses, daffs, and tulips for early
spring color, my
roses bloom right after that and you can buy the subzero
roses so that they will come back.
Those are just a few suggestions. I'm sure others will chime in with their favorites.