Plants need transplanting for a variety of reasons: they may be doing poorly in their original site, they may have grown too large for the site, they may need protection from wind or they may not receive adequate light. Plants do best when transplanted in cool weather, so avoid working on hot sunny days, since that adds stress.
Plants must be fully transplanted and adapted to their new location by late fall, especially in colder climates where winter frosts can harm them. North Dakota State University advises gardeners to wait until plants have dropped foliage for the fall and transplant them just after, so that plants can adapt and absorb water through their roots before the soil freezes. If you don't want to transplant in autumn, move plants in the early spring. Late spring to summer is the worst time of year to transplant plants.
Perennial plants respond well to fall transplanting. Woody shrubs and trees also fare well when transplanted in autumn. Sensitive perennials can be transplanted into containers and moved indoors for the winter.
Water your plant until the ground becomes saturated for two to three days before transplanting--this makes the process easier. Prepare the new site before you dig up your plant. Dig a hole and remove rocks, sticks, weeds and debris. Make sure the hole is roughly twice as large as your plant's root ball. Jab your shovel at the bottom of the hole to loosen the soil--this will help the plant's roots to quickly adapt. Once the hole is ready, dig up your plant.
Begin digging at roughly twice the distance of the plant's root ball. GardenLine estimates that you should aim to dig out 9 to 12 inches of root ball per inch of trunk diameter--it's important to retain soil with root and to cut into roots as little as possible. As you dig, you'll see the roots; guide your digging so you gather all roots underneath the plant in a ball of soil. Gently lift the plant out of the earth once you've dug out the root ball. Carry the plant to its new location and place it in the hole so it sits at the same depth as it was planted before. Fill in the hole with soil, firming the soil around the plant's roots. Water the transplanted plant until the ground becomes saturated to complete the fall transplanting.
Fall transplanted plants need aftercare to get them settled before the winter. Water the plants to nurture the roots, since plants can become dehydrated over winter. Check the soil's moisture level 2 to 3 inches under the ground and water whenever the soil feels dry and crumbly. Mulch the soil around the plant with 3 to 4 inches of mulch, which helps keeps moisture near the plant and provides protection from the cold so your plant's roots continue to grow into the soil through the late fall.