Richard Bogren | 3/3/2017 3:04:52 PM
By Dan Gill
LSU AgCenter Horticulturist
(03/03/17) I take great satisfaction in telling gardeners about all the many plants that will thrive in our state. These plants are excellent choices for your landscapes and gardens because they have proven records of thriving in our climate. But many other plants will not do well here.
Over the years, I have often cautioned gardeners about a particular plant choice. Now, I have to be careful here. I can’t tell you how many times I’ve given lectures and mentioned this or that plant will not grow well here, only to be collared by a gardener afterward who tells me the plant grows just fine for them. I long ago stopped saying that a plant will not grow here. I now hedge my statements by saying things like “This plant is challenging and generally does poorly here,” or “Gardeners I’ve talked to in this area found this plant did not thrive for them.”
Of course, sometimes I am asked about a plant that I can find no evidence has ever been grown here. I don’t necessarily discourage gardeners in those situations, unless the plant comes from a vastly different climate than ours. But I do make it clear they are on new ground. Only adventurous gardeners who are not afraid of failure and can afford the loss should select plants that do not have a proven track record where they garden. Still, these excursions into the unknown may lead to discovering new and wonderful plants that thrive in our climate.
When I do have some idea about a plant’s poor performance in our state, I think it can be just as important for gardeners to know which plants are likely to fail as those that are likely to succeed. At this time of year, when you are looking at garden catalogs full of mouthwatering pictures, it’s good to take a deep breath and do some research before you pull out the credit card or checkbook and send in an order. The plants you find at local nurseries are almost all well adapted to our area, but there is no such assurance when mail ordering from a catalog or the Internet.
Here are some of the more dubious plants I’ve gotten the most inquires about over the years.
Large, round clusters of beautiful flowers and dark green, leathery leaves make rhododendrons highly desirable garden plants. They are related to the evergreen oriental azaleas so common in our gardens and our deciduous native azalea species as well. All of these plants belong to the genus Rhododendron. Unfortunately, all of those gorgeous rhododendrons you see in the catalogs were bred from species native to areas colder than ours. We have found that these northern rhododendrons languish and die here.
If you would like to try rhododendrons in your garden, look for the Southgate rhododendrons. They were bred to grow in the Deep South, come in several colors and are part of the Southern Living Plant Collection.
Lots of people are planting fruit trees this time of the year. LSU AgCenter research stations have evaluated most types of commonly grown fruits. The good news is that Louisiana gardeners can grow a wide variety of fruiting plants, including apples, peaches, nectarines, pears, plums, muscadine grapes, figs, persimmons, pears, blueberries and blackberries. Make sure you choose cultivars adapted to our state. For more information on this, go to the LSU AgCenter website and search for “fruits and nuts.”
Unfortunately, a few fruits have not done well enough to recommend. Sweet and sour cherries (and also the ornamental Japanese flowering cherries), apricots, almonds and kiwi fall in this category. In areas of the state with alkaline soils, it is extremely unlikely you will be successful with blueberries.
So even within the state, a particular plant will grow well in some areas but not in others. This is especially true between north and south Louisiana. Many of the plants we can’t grow well in Louisiana need more cold in the winter than our climate provides. Because north Louisiana winters are a little colder and longer than those in south Louisiana, plants that need the cold tend to do better there. South Louisiana, on the other hand, has more success growing tender, tropical plants because of the milder winters.
Peonies and lilacs are perhaps the two plants I’ve gotten the most inquiries about over the years. These plants are highly desirable and very easy to grow up north. Alas, winters in south Louisiana are too mild for either to be really successful. In the far northern parts of Louisiana, however, gardeners are having good success with peonies. Bearded irises and forsythias grow well in north Louisiana but do not perform well at all in south Louisiana.
In south Louisiana, tropicals like gingers, bird of paradise plants, palms, banana trees and elephant ears are commonly used in landscapes. Typical mild to moderate freezes may damage tropicals in winter but rarely kill those that reliably return. Many of these tropicals would be less likely to survive the typical freezes of a north Louisiana winter.
So be careful when making plant selections, particularly by mail order. If you are unfamiliar with a plant, check locally appropriate references or with local professionals before you purchase it.
Southgage Brandi rhododendron is one of a series of heat-tolerant rhododendrons for the Lower South that have been developed in Louisiana by Dr. John Thornton of Franklinton. Photo by Allen Owings/LSU AgCenter
Rabbiteye blueberries have been named a Louisiana Super Plant. Photo by Allen Owings/LSU AgCenter