New plants are a joy, but taking a potted specimen from the greenhouse or nursery and instantly planting it out into the garden may not give the best results. Before you can plant into your garden, you'll need to condition a butterfly bush to acclimate it to the fluctuations of temperature, humidity and wind that it will experience outside that didn't exist in the greenhouse. Give your plant approximately two weeks to become accustomed, or hardened off, to outdoors before you plant it into its permanent location where it can work on root development with less stress.
Set the potted butterfly bush outside in a location where it will receive at least six hours of direct sunlight a day. This location needs to be against a solid fence or wall, preferably a corner, which blocks heavy winds.
Water the pot to thoroughly moisten the soil, but make sure the pot isn't waterlogged or resting in a saucer of standing water. Even once they are in the ground, butterfly bushes don't like too much water in the soil, so weekly watering should be all you'll need to maintain the plant.
Spread a layer of compost over the top of the soil in your pot to act as a mulch and retain moisture in the soil which will be wicked away more quickly outside. Since butterfly bushes don't thrive on many fertilizers the compost will also add extra nutrients to the soil.
Leave the plant in this location for a week. After this time move it to the spot where you intend to plant it, allowing the potted butterfly bush to sit for another week in its pot at this permanent location which may or may not be blocked from wind.
Transplant the bush into the ground by digging a hole twice as large as the pot is in and replacing half of the soil with compost. Transfer the bush from pot to soil and be sure to water the plant each week during the growing season.