Roses have earned the dubious privilege of being considered sensitive and difficult to grow. This is not entirely true of course, a rose planted in a climate that favors its development requires a lot less maintenance than your average perennial. They do have a list of things they absolutely will not put up with, and no amount of doting will support them in the presence of the following conditions:
I don't know if you ever noticed, but purple flowers pick up a metallic sheen in bright sunlight. The beauty in the picture is Krossa Regal, a compact hosta variety which blooms very reliably in August.
1) Lack of sunshine. If you don't have full sun exposure, spare yourself the anguish and don't try roses. It is heartbreaking to watch them diminish pitifully, year after year. The good news is that you can move them before they succumb to their bitter fate, but they lose years recuperating their wasted resources. Give them sunshine or don't plant them at all.
2) Overcrowding. If a rose doesn't have "elbow" room it will harbor every pest there is. Overcrowded roses are stressed and their resistance to disease diminishes. Less air movement around their canes also means their foliage doesn't dry off quickly, thus providing breeding ground to fungi. Respect the planting space recommended by the breeder, or at least a foot and a half in each direction.
3) Heat. I was surprised to learn that my roses absolutely hate hot weather. A thick layer of mulch can help keep their roots cool and moist during the dog days of summer but heat stress increases their vulnerability to disease. Sweltering days also bring along Japanese beetles, which eat them into stumps.
4) Wet weather. Black spot, mildew, rust, enough said. If the summer is rainy, there is not much you can do about it. They will develop black spot instead of flowers, an object lesson about the unfairness of life.
5)Unsteady soils. Roses need good heavy soil weighing down on their roots to facilitate their access to water and nutrients and anchor them steadily against harsh winds. They are not the kind of plants you use to stabilize soils and will never get a good start unless their roots are secure. Don't plant them on slopes or in silty dirt.
6)Poor nutrition. If you want your rose to bloom you need to ensure its proper nutrition. Avoid excessive use of fertilizer which will build up in the soil over time and make it too salty to use, but ensure there is a good balance of potassium, nitrogen and phosphorus because they are heavy feeders.
I just realized I forgot to move the gorgeous Raspberry Sorbet peonies at the end of fall and now they are going to spend another year trying to assert their needs in the midst of the rose thicket.
Because of the one-two-three year garden rule and their slow start (they didn't come out of the ground at all during the first year), I forgot about their space needs and planted lots of aggressive sun loving plants on top of them. Now they finally decided to come out and have to wrestle a thorny and voracious Hansa for food and sunshine. To this end they grew really tall, weaving themselves through the rose canes, which makes their flowers look like weird gigantic roses, illusion further enforced by the fact that the two plants' flowers have similar shapes and colors and bloom at the same time.
Peonies are not demanding plants, as long as they have sunshine, they are happy. The clumps grow over time, but unlike other perennials, don't require dividing in order to thrive. Be careful about powdery mildew, a pest that tends to perpetuate in the ground from one year to the next and cover the foliage with unsightly white dust towards the end of summer. It won't harm the plants, but it can be stubbornly persistent if not addressed. Like any fungal disease, treat until the symptoms are no longer present, no matter how long that takes.
Peonies are very long lived and ruggedly resilient; they are not daunted by poor heavy soils, lengthy droughts, killing frosts or garden pests, the only things they really require are plenty of sunshine and undisturbed roots.
If you do want to divide peonies, dig them up in the fall, break apart the tubers into separate pieces, each containing optimally three to five eyes and plant them, eyes up, in the new location. If you don't want to disturb the whole plant, you can literally cut a slice of it, roots and all, for propagation purposes, and the mother plant won't be worse for the wear.
Don't plant them too deep, no more than two inches under the surface or even one for warmer climates, otherwise they'll take forever to come out of the ground. Don't expect any performance out of peonies the first two or three years, they need that time to get established and stock up energy reserves for flower production. Don't worry about the wait, once they start blooming they become a care free garden staple that will delight you for many decades.