Peonies are very easy to grow, and yes they do need cold winters to thrive. That being said, it never hurts to cover them up for the winter, I use leaf mulch. They need full sun (6 hours + a day). mine have never bloomed for me the first year or two. I would think it would be OK to plant them now. Find a good sunny location with plenty of room (read the tag on the container for proper spacing) and good draining soil. You can move them n the future if need be, but they pout for a few years (for me anyway) and don't bloom. Good luck and enjoy. . . !

I usually order my peonies online from a specialty vendor, because you can get more interesting varieties than from the local garden store. These come bareroot for fall planting. If you buy a potted peony from your local garden store, I don't see any reason you can't plant it now, as long as you try not to disturb the root ball too much, and you kept it watered until it established. (But peonies don't like standing water - plant somewhere sunny and well drained.) Herbaceous and intersectional peonies will do very well in zone 4-5.

I am in Z5a and would never bother to cover peonies in the winter. I don't know of anyone who does and they live to be 100+ years.

I usually mulch my bareroot peonies the first winter after they are planted, to prevent frost heave from shifting the main root and bringing it too close to the surface and possibly damaging the new roots. But after the first season, I never mulch, and I have never had any problems.

I mulch because it's so darned dry here there would be no moisture retention at all if I didn't! Do you plan to buy your peonies locally, Rosewinda? Bareroot peonies should best be planted in fall. I know a lot of the stores offer them in the spring and that's okay, too. Planting the bagged, big box store peonies in the spring can seem like an exercise in throwing money away; quite often you don't see any growth at all that 1st spring/summer. If you get them at the right depth though they'll normally grow the next year. They're typically a lot smaller roots that those you buy bareroot from a large grower online but the price difference makes up for it, you can normally get a bagged root from Walmart for around $5.00 where the same variety will be $17 or more plus shipping from the online growers. The ones you get from a good grower selling online will often bloom 1st spring after being planted in the fall, though, where you'll wait at least an additional year for the Walmart ones. If you're buying them potted from a local nursery you can plant them out just about anytime, wouldn't wait for the heat of summer to try it, though!

As for roses, I've been assured that they will grow in the colder zones but you have to plant them way deep and go for a hardy variety. I'm trying them for the first time in 15 years this spring, really hoping they're right! I bought 6 or 7 different varieties and planted them several inches deeper than I'd have thought wise based on a local rose grower's recommendation, we'll see how it goes!

This pertains to roses:

You can grow many roses in zone 5. As Lizin said if you go with the tender ones you need to plant the bud unions 4-6 inches below soil level. Otherwise you go for the hardy ones such as many of the OGRs, Rugosa, Explorer & Parkland, hybrid Spinosissima roses.

Just check on the rose forums and you'll be quite surprised!

A garden of roses and peonies could be something...