Mandevilla tubers, part of the plant's root system, store energy and nutrients similar to a rhizome, which fuels the plant during the winter months. The tubers won't grow into a new plant on their own but instead are just one portion of a healthy root system. Whether you transplant mandevilla to a new container or plant a new plant in a garden bed, leave the tubers and roots intact so the plant has the energy it needs to reestablish and grow healthy in its new home.
Add 1 to 2 inches of humus or compost to a partially shaded, well-drained garden bed. Work the compost into the top 8 inches of soil. Mandevilla thrives in rich soils but can't tolerate soil that remains wet and soggy.
Dig the planting hole to the depth of the nursery pot. Make the hole two to three times as wide as the pot.
Lift the mandevilla from the nursery pot, brushing away soil from the roots and tubers. Loosen the roots gently with your fingers but avoid bending or breaking the tubers off the plant.
Set the mandevilla in the planting hole. Add soil beneath the root system, if necessary, so the top of the roots and tubers sit just below the soil surface.
Fill in the hole around the tuberous root system. Water the soil thoroughly to settle it after planting. Water the plant throughout summer when the top 3 to 4 inches of soil feel dry.
Install a stake or trellis behind the mandevilla so it has a structure to climb. Guide the first shoots onto the trellis. The plant climbs on its own once established.
Plant mandevilla outdoors when nighttime temperatures are regularly above 15.6 degrees Celsius and frost danger is past. Dig up, pot and bring in the tubers before temperatures drop below 10 degrees Celsius. When transplanting mandevilla tubers to a new pot, choose a container one size larger than the old one. Mandevillas require repotting every one to two years.