I Have a Mandevilla Plant That Suffered Frost Damage and It Looks Dead: Will It Come Back?
Mandevillas (Mandevilla spp.) are prized for a vigorous growth habit and showy, trumpet-shaped flowers available in shades of pink, yellow, red and white that appear on the plants continuously throughout most of the growing season. According to Clemson Cooperative Extension, there are over 100 mandevilla species. These tropical plants grow as perennial vines in U.S. Department of Agriculture plant hardiness zones 9 to 11, although they are potentially cultivated as annuals or overwintered indoors across a much broader range.
Frosts and even extended periods with temperatures below 55 degrees Fahrenheit can injure a mandevilla, sometimes extensively enough that it is not clear if the plant has survived.
If your mandevilla suffered frost damage, you'll need to inspect the plant to determine whether it really is dead, or whether it still has life left in it.
Inspection and Immediate Action
Flowers and leaves may drop off of a frost-damaged mandevilla fairly quickly, but it may not be as easy to tell if stems survived. To check if a section of the stem is still living, use your fingernail or a sharp, clean knife to gently scrape off a small section of outer bark and observe the color of the underlying tissue.
If it is green, that part of the plant is still living. If the tissue is brown or black, it is dead. If the mandevilla was not completely killed by the frost, it will still benefit from regular irrigation, although it requires less water than it did before it was injured and when it was actively growing.
Whenever rainfall is inadequate, irrigate the mandevilla deeply so that the soil around the plant's roots never dries out completely, or whenever soil a few inches below the soil surface near the mandevilla base feels dry to the touch.
Put off Pruning
Although it may be tempting to prune off dead parts of the mandevilla as soon as you determine the extent of the damage, wait to trim off dead mandevilla stems until all danger of further cold injury has passed, advises the University of Florida IFAS Extension. The dead portions remaining attached to the plant offer slight protection against further cold injury. Pruning prematurely can also stimulate a flush of tender new growth prone to injury during any additional cold weather.
Perform Corrective Pruning
Once you determine the approximate extent of the damage, or new growth has started to emerge and all danger of cold damage has passed, you can prune off dead sections of the mandevilla. Use sharp, clean pruning shears or loppers to make angled cuts into living, green tissue just above a bud.
If it appears as though the mandevilla stems were killed back completely, with no green tissue visible aboveground, cut the stems to about 6 inches above ground level. If the root system survived the cold weather, new growth may still emerge within a few months.
Prevent Future Problems
If the mandevilla survives, or if it does not and you opt to replace it with a new mandevilla species, certain care practices can help to minimize the likelihood that the mandevilla will suffer damage as extensively in subsequent years. Maintaining a layer of organic material mulch 3 to 4 inches thick over the ground around the mandevilla regulates soil temperature and helps to protect the mandevilla roots and crown against injury.
Make sure the mandevilla receives sufficient irrigation throughout the growing season, but reduce those waterings in the weeks leading up to any possible cold events, says Arizona Cooperative Extension. Also, do not apply fertilizer to the mandevilla in late fall or early winter, as this can encourage a flush of tender new growth.