If you despair about ever growing anything in a hot, rocky spot in your garden, then "Autumn Joy" sedum (Sedum "Autumn Joy," Sedum x "Autumn Joy" and Sedum "Herbstfreude"*) may save your sanity. Hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9 or zones 3 through 11, depending on the source, these perennials with gray-green leaves and flowers that change from white buds to dark pink, then bronze and finally copper are simple to transplant.
When to Divide and Transplant
Because sedum is a fall-bloomer, dividing and transplanting it in early spring -- as soon as the ground can be worked and the area's annual average last frost date has passed -- produces the best results and lessens the risk of transplant shock. If you start early enough for each divided root system to establish itself fully before the heat of summer, the risk of transplant shock is even lower. Pick an overcast day for transplanting. An overcast day when light rain is forecast for the following few days is even better.
How to Prepare the New Site
"Autumn Joy" sedum adapts to even the driest, rockiest soil, but a sandy, well-drained site in full sun helps it thrive. Turn up the new planting site's soil to a depth of about 15 inches to loosen it. Incorporate about a 3-inch-thick layer of compost in the loosened soil. Make each planting hole about twice the diameter of its future plant's root ball and about as deep as the plant's current growing space or container.
How to Dig Up and Divide the Plant
Water your "Autumn Joy' sedum the day before you plan to divide and transplant it. Damp soil makes it easier to remove the plant from the ground without exposing it to excessive trauma. Use a spading fork to loosen the soil on all sides of the "Autumn Joy," digging about 5 inches from the plant. Slip the fork underneath the plant, and use it to lift the whole plant out of the ground. Shake excess soil from the removed plant, and use a disinfected, sharp knife to separate its clumps if you want to divide the plant. Disinfect the knife before using it by wiping it with ethanol or isopropyl alcohol or by soaking it for 30 minutes in a solution of one part bleach to nine parts water.
How to Place the Sedum
Space each "Autumn Joy" plant about 6 inches from other plants, and place it in its prepared hole so that the top of the root ball is level with the surface of the surrounding soil. Press soil around each plant's roots firmly to eliminate air pockets, and water the plants' soil well.
During the first few weeks after planting, ensure the soil receives about 1 inch of water per week, supplementing rainfall as necessary. Once established, "Autumn Joy" is drought-resistant so doesn't need frequent watering.