Vinca is very drought-tolerant and has an extremely long blooming season. It can also tolerate the highest temperatures we face during the summer growing season.
Great improvements have been made in vinca flower colors and varieties during the past 25 years. In the 1980s, gardeners had few choices in terms of vinca growth habits, flower colors or disease resistance. In the 1990s, new forms and new flower colors arrived with rapid expansion occurring between 2000-2005.
Vinca flower colors now include pink, deep rose, red, blush, scarlet, white, white with a red eye, lavender blue, peach, apricot, orchid, burgundy and many others. You can have vinca varieties that are upright and vinca varieties that are spreading. Plants generally grow 18-20 inches tall with a spread of 12-14 inches. Spreading types, though, have more trailing or ground cover habits and reach only 6-8 inches tall (at the most) with spreads of 18-14 inches.
We do have vinca problems in the landscape, and based on the number of calls with vinca issues this spring, this is a bad year for vinca. This is surprising considering we now have disease-resistant varieties and we had a very dry spring and early summer.
The main disease culprit is a fungus called Phytophthora, which always is present in our soils. It is often responsible for root rots and crown rots, and it attacks many types of plants. This fungus causes a disease seen shortly after planting, but it also can be found later in the year.
Rhizoctonia is another disease common on vinca in Louisiana. It normally shows up in the summer after plants are established. Plant pathologists can also find Botrytis (gray mold) and Alternaria (leaf spot) on vinca in summer and fall.
To get the best performance out of vinca in your landscape, consider the following LSU AgCenter recommendations:
•Begin with good quality plants. Inspect plants obtained from the greenhouse grower or retail garden center for healthy roots.
•Select a full-sun location. Vinca need at least eight hours of direct sun daily for optimum performance.
•Properly prepare the landscape bed to allow for drainage and aeration. Raise the bed at least 6 inches if drainage is questionable. If beds are already established, all debris from the previous planting needs to be removed. Possibly, mulch should be removed also and add another couple inches of landscape soil prior to planting.
•Although late April through early May is the ideal first planting date for the spring, you can continue planting vinca through the summer. The main thing to remember is that vinca love warm soil.
•Plant so that the top of the root ball is level with or slightly higher than the soil of the bed. Proper spacing also is important because a crowded planting limits air circulation and can create conditions more favorable to disease development. Space transplants at least 8-10 inches apart. The more quickly plants grow together, the higher the likelihood of disease moving through foliage later in the year.
•Mulch to decrease splashing of rainfall and irrigation water from soil onto the lower stems and foliage of the plants. Bedding plants should be mulched to a depth of about 1 inch. Pine straw is the preferred mulch material.
•Manage irrigation properly. This is the main culprit in plant decline in commercial landscape beds. Vinca need very little irrigation once they’re established. Avoid regular overhead irrigation. Even if the landscape bed drains very well, an adequate volume once a week is the most water that should be applied.
•Don’t plant periwinkles in the same bed year after year. Rotate them with other summer bedding plants that like sunny locations, such as blue daze, lantana, pentas, angelonia, scaevola, verbena, melampodium or sun-tolerant coleus.
Varieties of vinca available in Louisiana include Pacifica, Cooler, Mediterranean, Victory, Titan, Nirvana and Cora series. Cooler and Pacifica are older varieties that still perform well with correct care. Mediterranean vincas spread and should be planted only in hanging baskets and containers. Titans have the largest flowers of all the vinca groups. The newer and more expensive Nirvana and Cora vincas have genetic resistance to Phytophthora. A few other vincas we have evaluated at the LSU AgCenter recently are not being sold in any significant quantities in Louisiana.
It is late in the bedding-plant season, but pay attention to vinca in landscapes. Are you noticing them looking good or looking bad? Try to figure out why a particular planting is performing well or not performing well. Vinca can have trouble through the summer and fall if proper practices are not followed, so consider the above options to improve your success.
For more information, contact Dr. Chris Robichaux, county agent/area horticulturist, St. Martin/Iberia Parishes, at 332-2181 or 369-4440.