Over many decades, we have come to count on colorful, sturdy vinca (Catharanthus roseus) as the workhorse of our summer gardens. With its pretty pink, white and purple blooms clustered en masse on a low mounding plant, vinca have served as beautiful and dependable bedding plants that can stand up to the hottest days in south Louisiana.
But in recent years, this bedding plant’s luster has faded as it has increasingly been subject to a type of fungal blight that shrivels its leaves and can eventually kill off every vinca in a bed. Blame it on a type of phytophthora, a fungus that lives in the soil.
“It’s always there in the soil and just waiting for the right weather conditions and a susceptible plant to attack,” said Allen Owings of the LSU AgCenter. “Spring weather and the home gardener’s practices both play big roles in determining the plant’s reliability.”
Gardeners can’t change weather patterns, but they might want to pay attention to them to decide whether to plant vinca in their warm season beds.
“Cool, wet springs help the fungus thrive and may indicate there will be problems with vinca after it is planted,” Owings said. “On the other hand, a warm, dry spring discourages the fungal growth in the soil and lessens the chance that vinca will exhibit blight.”
But vinca is a must-have plant in the summer garden for many gardeners, and Owings says there are plenty of steps that can be taken to ensure the best possible outcome.
“The No. 1 problem is that gardeners plant vinca too early in the season, because that’s when they begin showing up at garden centers. You don’t want to plant them February through April and should wait until after May 1,” he said. “That gives them the best chance. And don’t try to make a low-maintenance plant like vinca, that’s highly drought tolerant, into a high maintenance plant by watering them all the time. Let them dry out.”
Once the fungus attacks the roots, it spreads upward to the crown and eventually becomes airborne. There are no fungicides available to the home gardener that can effectively kill the fungus, Owings said.
“The best you can do when you see the wilt starting is to pull the affected plant out of the bed and make sure you get all of its roots. It’s not a great alternative, but at least it can help keep the disease from spreading to other vinca in the same area,” he said.
Owings said that well-drained soil and direct sun for eight or more hours a day can also help vinca thrive and avoid an attack.
He cautions against planting them in the same bed every year.
“Just as you would rotate your tomato crop, you would rotate where you plant your vinca,” he said. “And never plant them in a bed where phytophthora has been a problem in the past.”
Plants should be spaced 10 to 12 inches apart (for good air circulation) and with the top of the root ball level with or slightly above ground level to ensure the roots don’t become soggy.
Using Owings advice, it’s entirely possible to install vinca in a home garden and get good results.
If the checklist of when, where and how to plant vinca feels a little too onerous, Owings said there are a number of warm season bedding plants to use in its stead.
“And don’t forget lantana — it likes the same kind of dry conditions that help vinca thrive.”