Take a stem cutting from a healthy Mandevilla plant in late spring or early summer. Use a sterile, sharp knife to remove a piece of stem about four or five inches in length. Strip off the leaves from the lower half of the cutting.
Fill a planting container with potting soil. Dip the cut end of the stem in rooting hormone and bury it, cut end down, in the potting soil. The leafy section of the stem should be above the soil. Cover the planting container with a piece of clear plastic or put it in a plastic bag. The plastic will act like a miniature greenhouse, keeping the plant warm and moist. If the soil appears to be drying out, remove the plastic, mist the soil, and replace the plastic.
Transplant the Mandevilla cutting to a larger pot after it takes root, which will take three to four weeks. You can tell if the plant has rooted by tugging gently on the plant. If you feel slight pressure when you tug, the Mandevilla has taken root. Move the planting container to a sunny window and leave it until it until early spring, when all danger of frost has passed. At that time, it can be planted outdoors.
Plant the Mandevilla where you are sure the soil has good drainage. If you notice water pooling after a rain, this is an indication of poor drainage, and that you need to select a different planting site. Mandevillas can be harmed by excessive heat or sun, so they should be planted in a place that will be shady during the heat of the day.
Water the Mandevilla plant two or three times a week, and more in hot, dry periods. The soil should be kept moist, but never let the roots stand in water. Fertilize the plant once a year with a good all-purpose fertilizer. Follow the manufacturer's directions regarding specific details.