We start shipping peony rhizomes in mid-September each year. We can usually ship through until the 3rd week of November. Orders go out on Mondays and Tuesdays so as to ensure that you receive your plants before the weekend, thus minimizing the time that the roots are in transit.
It is important to prepare the planting area early, by digging a hole of at least 1 cubic foot per plant and enriching the soil with organic material (preferably of the well decomposed cow manure sort). The ideal PH for peonies is 6.4 and so if necessary please make amendments.
Peonies like full sun, well drained soil and a southern exposure (don't we all). They will always perform well under compromised conditions. However, if given a choice then remember that they love the sun.
Peony roots have two growth spurts per year, in the spring, and in the fall. It is important that they get adequate water at these times. During the summer it is critical that they photosynthesize to their maximum potential, and so they should be kept weed free with as many leaves left in tact as is possible. Peonies that are 4 years old, or more, can afford to have 50% of their stems harvested for decorative purposes. These harvested stems will make fabulous cut flowers without seriously affecting the plant's long term performance.
Pay attention to how they are planted, as if planted too deep they will not flower, too shallow and they will heave in extreme cold. The colder your winter the deeper they need to be planted.
In Maryland we plant so that the eyes are 1" below the final settled soil level.
In Pennsylvania we plant so that the eyes are 1 1/2" below the final settled soil level.
In upstate New York we plant so that the eyes are 2" below the final settled soil level.
The planting depth is important because the plant's eyes need exposure to cold degrees in order to vernalize. The further south you are growing the less soil insulation (from cold) required and the eyes need to be closer to the surface. However, many growers in the north mulch before winter, thus providing protection from extreme cold.
We recommend that plants should have 2 feet between one another, so as not to compete for root space. Mature plants have a wing span of as much as 5 feet.
In choosing your varieties to plant, you should be aware that the singles, semis, and Japanese, varieties establish themselves faster than the doubles and bombs. they generally flower earlier, more prolifically, and are more durable when it comes to holding their flower in the garden. These plants tend to shed rain water and are thus less prone to lodging. On the flip side the doubles and bombs make superior cut flowers with a huge varietal difference in aromatic fragrance.
After blooming it is a good practice to cut off the spent flower. If left the plant will go to seed, thus draining precious energy that should be conserved for the next season's bloom.
In writing this I have almost convinced myself to go out and start digging dividing, and planting. Roll on September with those beautiful perfect blue sky days, when everyone should be planting peonies en masse.
Good luck! I look forward to working with you.