Mandevilla seeds come from the center of the calyx. The seed pods are around 4-6 inches long and hang in pairs in the shape of an inverted V. When the pods dry, they will turn brown and split open exposing fluffy seeds that have fluffy aerials (like dandelions) to help disperse them. With the tail on, soak the seeds for 12 hrs. then plant and cover with soil. Keep at a temperature of 65-75. Should germinate within 30 days.
Can be easily propagated from cuttings to make new plants. The best time to take cuttings is in the spring but they can also be taken in summer/fall. Take 2-3 ” tip or side shoot cuttings that have new growth that is beginning to firm (not new light green growth) remove all but the 2 top leaves. Dip the cuttings in rooting hormone and place in sandy peat soil mix. Keep the cuttings moist and humid with bottom heat of 68-77F (20-25C). To maintain humidity, place them in a plastic bag (opening periodically to release excess moisture) . Keep cuttings in shaded area, out of direct sunlight. It can take 20-70 days to root.
For softwood cuttings (before new growth begins to firm), remove the soft tip and lowest pair of leaves. When inserting into the medium predibble the hole and insert cutting, gently firming the soil around the stem. Water in with a fungicidal solution to avoid fungal infection. When roots form, plant in 4″ pots and pinch back new growth to promote side shoots and bushier plants.1
Treat it as a houseplant or store it in a dormant stage.
Mandevilla as a can be trimmed back to make it manageable and needs a sunny window to flourish indoors. Water once a week. You will get some leaf drop due to lower light and humidity indoors.
Dormant stage — Another way to winterize mandevilla is in a dormant stage in a garage or cool basement with temperatures around 45-55F. Cut it back to about 12 inches above the soil line. Treat for insects if needed. Keep it dry but not completely dry. Check periodically for soil moisture. Mandevilla will eventually drop all its leaves. The important thing to keep in mind is that you want to keep it alive it through the winter.
In the spring, some of the spindly winter growth may be pruned back and when new shoots develop move the plant to a sunny window. Pinch the new growth to get a bushier plant. Repot in fresh soil and set outside when danger of frost has passed.
1 “Gardener’s Supply Plant Care” http://hortchat.com/info/propagate-mandevilla