Dipladenia is an old botanical genus name for what today is more commonly referred to as mandevilla vines (Mandevilla boliviensis and Mandevilla splendens). Kirsten Albrecht Llamas, author of "Tropical Flowering Plants" mentions that the names dipladenia and mandevilla continue to be used interchangeably. Native to the tropical woodlands in Central and South America, mandevilla vines develop tuberous roots and woody stems that twine and climb on trellises, fences, posts or other nearby shrubs. Where winters are cold, mandevilla vines are grown either as houseplants or summertime annuals outdoors that live until the fall frosts and freezes kill it. A member of the dogbane family, Apocynaceae, mandevilla vines release milky sap when a leaf or stem is cut; exposure causes skin irritation in some people.
Measure the size of the soil root ball of the mandevilla growing in the nursery container. Using a tape measure or ruler, note the depth (height) of the root ball as well as the diameter of the root ball.
Select a good planting site in the garden for the flowering vine. Avoid any location that doesn't receive at least four hours of direct sunlight daily or if the soil is hot, dry sand or a wet, soggy condition. The ideal soil is crumbly and drains well after rains, never flooding.
Dig a planting hole that is the same depth as the root ball but two to three times as wide as the root ball's diameter. Use a garden shovel.
Incorporate 3 to 6 inches of organic matter like compost or well-rotted manure into the pile of soil removed from the planting hole. Mix it in well and evenly with the shovel. Pulverise any large clumps of soil or organic matter to make a crumbly, fine-textured soil.
Remove the mandevilla vine from the nursery container and place it in the centre of the planting hole. Check the planting depth, as the top of the root ball must match the top rim of the planting hole. You do not want to plant the vine too deeply. Remove the root ball and add soil in 1-inch increments and replace the root ball into the hole until it rests at the proper depth.
Scratch the sides of the root ball gently with your finger tips to loosen the soil and roots from the root ball mass. Do not destroy the structured mass of the root ball, but loosening the roots helps encourage new root growth outward into the soil rather than remaining in the shape of the root ball. If the root ball is a firm mass of roots, slice into the root ball with the garden shovel in three or four equally positioned spots on the root ball. Cut no deeper than 1 inch into the root ball mass with the shovel blade.
Back-fill the planting hole with the amended soil, tamping it down gently with finger as the hole fills. Fill the hole until the soil line is even with the top of the plant's root ball. Use excess soil to create a small berm in a circular ring around the plant. This creates a watering basin to pour in water from a sprinkling can or hose.
Add 2 to 3 gallons of water to the planting area at a slow pace and allow the water to soak into the soil around the root ball. This watering compacts the soil and eliminates air pockets, bringing the mandevilla's roots into direct contact with soil particles. Add additional backfill soil if after the watering the soil level compacts and settles below the top of the root ball. Remember, you want the soil in the hole to match the top of the root ball of the vine, just like it had grown in the nursery container.
If planting mandevilla in a container, to grow on the patio or as a houseplant, do not use topsoil. Purchase a mixed potting soil to use in the container since it is free of worms, pathogens and will not compact after being watered and dries. Choose a container that is 2 to 3 inches larger in diameter than the root ball of the mandevilla vine. Too large a container often leads to uneven soil moisture, as the root ball dies out more quickly than the soil around the edge of the large pot.
Soils with a high pH (alkaline) or garden locations with hot, blazing sun can lead to yellowed leaves and diminished health of the mandevilla vine. "A-Z Encyclopedia of Garden Plants" recommends placing the plant in a sunny location that receives some afternoon shade to prevent leaf yellowing or plants from heating up and needing additional watering.