Crimson mandevilla (Mandevilla sanderi 'Sun Parasol Crimson') is a perennial vine with deep green leaves and bold, dark red flowers. It grows up to 8 feet long and produces blooms continuously throughout the growing season. Temperatures below 45 degrees F will kill crimson mandevilla, and the plant must be brought indoors for the winter in U.S. Department of Agriculture zones 9 and below.
A site that receives full sun or light shade encourages healthy growth and abundant blooms. If planted outdoors, crimson mandevilla requires a location with proper drainage because the roots can't tolerate excessive moisture. The vine should be grown in a planter and moved indoors during fall in all but the warmest locations. Provide a sunny location protected from cool drafts if overwintered indoors.
The planting hole should be two times the diameter of the container the crimson mandevilla was purchased in and the same depth. Mixing a layer of humus with the garden soil adds nutrients and improves drainage. If growing in a container, a mixture made of two parts peat moss, two parts perlite and one part loam is ideal. Water the plant deeply right after planting, and place a trellis or other structure 3 to 4 inches behind the vine for support.
The soil of crimson mandevilla plants should be kept barely moist at all times during the growing season. Monitor container-grown plants closely to make sure they are getting the right amount of moisture. If yellow leaves are noticed, the plant is likely being over-watered. Reduce watering during winter months, when temperature and light conditions aren't as high. Feed with 15-30-15 fertilizer during spring and summer months. The plants require no fertilizer during winter. Cut the oldest portions of the vine back to soil level in very early spring. Trim the remaining stems to stimulate growth.
Pests that commonly infest crimson mandevilla include spider mites, mealy bugs, scales and whiteflies. Symptoms include leaf spots or damage, dropped foliage and white webbing. Spider mites and whiteflies can be dislodged by spraying the foliage forcefully with a garden hose. Mealy bugs and scale can be controlled with applications of insecticidal soap or horticultural oil. Keeping crimson mandevilla vines healthy is the best defense against these pests because they can significantly damage plants that are already stressed.