Marcia Mathews, Singh, Raghuwinder, Strahan, Ronald E., Fontenot, Kathryn, Fields, Jeb S., Kirk-Ballard, Heather
Get Your Soil Tested!
Never miss an issue of Horticulture Hints from the LSU AgCenter!
Visit the Horticulture Hints website at
Then click on the Subscribe button!
We think of fall as a time to wind down in the garden. Summer flowers are bloomed out, and the vegetable garden is picked over from summer harvest. For these plants, the party is just getting started. Here is a list of ornamental native plants that put on a show in the fall.
Witch hazel — American witch hazel is a deciduous shrub native to much of northeast Louisiana. It blooms in the fall with a mass of yellow fragrant flowers and also has yellow-orange fall leaf colors. Native, low maintenance, attractive to wildlife — there are more reasons to plant witch hazel than not.
Stokes aster — This attractive native perennial blooms through summer into early fall. The lavender colored blooms are very showy, and the plant itself is low maintenance and well behaved in the landscape.
Oak leaf hydrangea — This powerhouse native blooms during the summer, but the show carries into the fall with its dramatic display of red and purple fall leaf colors and dried flower heads. The contrast is a hard one to beat for fall landscapes.
Red spider lily — Not a true native, this well-established flowering bulb is a southern heritage plant and a sign of an approaching fall. The masses of red blooms cover the ground during the peak of hurricane season. No fall garden would be complete without spider lilies in the mix.
Fall blooming asters — Try a prairie garden with fall blooming asters, such as goldenrod, ironweed, eupatoriums, asters, joepye weed, sunflowers and blue mist flower. Seeds can be ordered and sown in the fall.
Research Associate, Northeast Research Station
Who doesn’t love daylilies? They are beautiful in bloom, easy to grow, easy to share and perform quite well in our climate. Daylilies do not require much from us in the way of upkeep and maintenance. While not heavy feeders, they can benefit from an application of 10-10-10 fertilizer in the spring as new growth appears. Pests are normally not a major problem. Aphids sometimes appear in the spring but can easily be treated with a horticultural oil or insecticidal soap. Daylily rust is the most common problem you will see, and heavy infestations require a fungicide application or total removal and destruction of all above-ground plant material. But do not let all that deter you!
For the most part, if you have your daylilies planted in a sunny, well-circulated area, they will most likely give you no problems at all for years to come. Every three to five years you may notice your daylily clumps start becoming crowded and flowering less and less. This is a sign that they need to be dug up and divided into more plants. Fall months are a great time to do this because the plants are entering dormancy and the stress of transplanting will not send them into shock or distress. During the winter months, transplants will settle in and come spring you will see flushes of new growth and blooms. Remember to divide in early fall, before first frost. Deciduous varieties will have died back and may be hard to find in the landscape. No matter the type — deciduous, evergreen or semievergreen — fall or even early spring is the right time to keep your daylilies in peak performance by dividing. After the last flowering cycle of late summer, monitor your daylilies to see if they need dividing. Check for dense clumps and ones that did not bloom as heavily or had smaller than average blooms. These are the ones in need. Pick a cool fall morning or evening to divide, as this will be an arduous task. You will need gloves, shovel, a garden knife and several 1-gallon nursery pots.
Some clumps will divide rather easily. Just pull clumps apart into individual smaller clumps. Some larger varieties form denser clumps. These must be cut apart with a serrated garden knife or even a kitchen bread knife. Your transplants will look raggedy for several weeks as the leaves die back, but this is perfectly normal and nothing to worry about. What you do want to see in the weeks following is some new growth coming out. If the plants were transplanted correctly up to the original soil line, the plants will rebound and start forming a firm root ball. You want to see new feeder roots forming. Once this occurs, usually after two to three months, you can go ahead and plant into the landscape or wait until spring when you are setting out spring bedding plants. Fertilize at planting.
Fall is also a great time to divide your other multiplying plants, such as irises, agapanthus, daffodils, cannas, elephant ears, liriope, gladiolus and hostas. A good way to remember when the best time is to divide a particular plant is to know when it blooms or performs. Spring and summer blooming plants are best dug up and divided in early fall before frost. Fall blooming plants, such as red spider lilies, are best dug up and divided in March to April when foliage starts yellowing and the plant is entering dormancy.
If you have deciduous daylilies, you may be tempted to mow or cut them back during summer and fall months after the blooming period has ended. This would result in a weak root system and poor bloom cycles the following year. The foliage acts as food for the roots, so it is best to leave it until it naturally dies back in the fall. Semi-evergreen and evergreen varieties can be tidied up by removing yellowing or dead leaves but leaving the foliage intact.
Most daylilies bloom once, putting on a big show in the spring. But the multiblooming varieties have become more and more popular over years, giving gardeners more bang for their buck in the landscape with two to three blooming cycles spring through late summer, even into early fall. Varieties like Stella de Oro make great compact border plants that bloom several times throughout the summer. Whether you have a repeater or a one-time bloomer, daylily maintenance leading up to dormancy in the fall is very minimal. Remove seed heads and woody flower stalks of daylilies to maintain their appearance and performance. If you keep seed heads pinched back, the plant will put more energy into making more blooms instead of seed production. The woody flower stalks do not affect plant performance if left but are unattractive and best removed for overall visual appeal.
Research Associate, Northeast Research Station
During the past year the Hammond Research Station, like most other places, was closed to the public. However, that did not stop us from planting our trials and maintaining the gardens. In fact, it was a fantastic year for the gardens. We felt very fortunate to be able to continue our work in the trial gardens, yet it was bittersweet. One of the best aspects of public gardening and planting the trials is to have everyone enjoy them and see the fruits of our labor. We decided this restriction would not suffice, and we set forth to build the Hammond Trials website to house all of our trial data. When the website was completed, we realized we had gone well beyond what we had set out to accomplish.
The Hammond Trials website has up-to-date information on all of our trial plants, including ratings, photos and observations. Moreover, we have updated cultural information, growing information and functionality/ecosystem services to the website. You can search for plant material by flower color, sun conditions, soil conditions, etc. You can also search for specific functionality, such as native or pollinator plants. We have many different categories and “tags” that can be searched to find the perfect plant. Furthermore, we have developed phase one of the “virtual walkthrough” where you can search for current trials by bed, just like you are in the garden. We are currently working on phase two of the virtual walkthrough, where you will be able to click on a virtual map and see up-to-date photos and information for the plants in each bed/garden. We also have a repository of video tours, research updates, Louisiana Super Plants and much more. With new features being added periodically and new plant ratings continually updated, we hope that you continue to use the new website as a fun guide and resource for all your landscape plant needs. The website will never be better than taking a stroll through the gardens, but it is very close. Come visit our website at app.lsuagcenter.com/hammondtrials, and make sure to bookmark the site. We can’t wait to hear what you think.
Jeb S. Fields, Ph.D.
Director of the Hammond Trials
The Louisiana Super Plant program is an education campaign of the LSU AgCenter that identifies superior plant material for Louisiana landscapes. Louisiana Super Plants have gone through rigorous trials at multiple AgCenter locations across the state of Louisiana and have been approved by Louisiana’s ornamental horticulture industry. Louisiana Super Plants are considered to be “university tested and industry approved.” The Louisiana Super Plant team has completed voting and selected the winners of the 2021 Louisiana Super Plants. While it was a very competitive year, we have four amazing plants that we can say with confidence are at home in every Louisiana landscape.
The first fall 2021 entry into the Louisiana Super Plants program is a longtime landscape favorite and native grass — Muhlenbergia capillaris — commonly known as Muhly grass. We wanted to build upon the native plant trend, and we just love native grasses. This is a workhorse in the landscape, thriving in many conditions and resisting almost anything it encounters. One of the few ornamental grasses grown for its flowers, Muhly grass blooms with lacy pink flowers in the fall when most other grasses are turning down for the year. Muhly grass does well in sun or part shade, handles wet and dry soils, and is just plain adaptable. Hardy throughout the state, muhly grass can grow 3 to 4 feet tall and spread 3 to 4 feet wide and can be enjoyed as a single specimen or planted in bunches. Muhly grass is very low maintenance, has year-round landscape appeal, and is one of the most drought-tolerant grass species available.
We absolutely love our cool-season color, and petunias are some of the best we can plant in Louisiana. That’s why we are naming Supertunia Mini Vista indigo our final 2021 Louisiana Super Plant. Supertunia Vista Bubblegum is still one of our favorite cool-season Louisiana Super Plants, and one of the best landscape petunias for Louisiana Landscapes; however, the Supertunia Mini Vistas bring some added excitement. The mini part of the name indicates smaller flowers, which add a unique look and feel to the landscape. While we really like all the Supertunia Mini Vista varieties, indigo brings a distinctive color, with individual flowers ranging from soft white to lavender to deep indigo. The extreme flower density and vigor ensure that these will be well received in any garden. Grown in full sun, these make an excellent addition for the cool season, providing color, texture and appeal from November through May. These also look great in containers!
For more information on the Louisiana Super Plants program, contact Jeb Fields at the LSU AgCenter Hammond Research Station or check them out on our new website: App.lsuagcenter.com/hammondtrials.
Jeb S. Fields, Ph.D.
Assistant Professor and Extension Specialist
Hammond Research Station
Heather Kirk-Ballard, Ph.D.
Consumer Horticulture Specialist
Falling out of love with the heat? No worries! Fall is around the corner, and there are plenty of cool-season vegetables and herbs to plant. Before planting, following a few of these tips will set you up for a successful harvest.
Now that the slate is clear, let’s move on to the fun stuff … planting!
For my last piece of fall garden advice, think about how much produce you can eat and or give away at one time. Like many of you, I am an overzealous gardener. Planting 50 to 100 heads of cabbage or broccoli at one time is nothing. But my small family can’t eat all of that. We give it away and waste some. To avoid this, use successional planting. This means divide your garden rows in thirds or quarters. Instead of planting the entire row in cabbage, plant one-third of the row. Then wait two to three weeks and plant the middle third of the row. Then wait two to three more weeks and plant the last third. This will help your fall crops, such as cabbage, broccoli, cauliflower, head lettuce and more, come in throughout the entire season rather than all at once.
Enjoy the Garden,
Kathryn “Kiki” Fontenot, Ph.D.
Associate Professor, LSU AgCenter School of Plant, Environmental and Soil Sciences
Louisiana usually stays warm well into the fall, and lawns continue to grow until nighttime temperatures dip into the 50s. So, be sure to mow and water your lawn as needed to keep it healthy.
If the fall feels more like summer, keep an eye out for armyworms in bermudagrass. Sod webworms and chinch bugs may still be active in St. Augustinegrass deep into the fall. Chinch bugs are most active in hot and dry weather. Insecticides such as carbaryl, bifenthrin and chlorantraniprole are effective insecticides for killing chinch bugs and moth larvae such as armyworms.
When summer is over it is time for your fertilizer spreader to hibernate until next year. Fertilizing warm-season lawn grasses during the fall with high nitrogen (summer-type) fertilizers or winterizing fertilizers containing high levels of nitrogen is not recommended for Deep South lawns. Stimulating fall growth of St. Augustinegrass, centipedegrass and zoysiagrass with nitrogen leads to increased large (brown) patch disease and winter kill. Bermudagrass may be fertilized into September, but I would not make any more applications of high percentage nitrogen-containing fertilizers after late August on St. Augustinegrass, centipedegrass or zoysiagrass.
If you would like to extend the green color in home lawns this fall, apply foliar iron spray or spreadable iron granules. This will give you a nice flush of green color without increased growth.
I am sure that you have heard of winterizer fertilizers. Potassium (the last number in the analysis on fertilizer bag) is the nutrient associated with winter hardiness and increased disease resistance with turfgrass. There is an advantage to having the correct amount of potassium in the soil when it comes to dealing with environmental stress. Get a soil test before applying high potassium fertilizer, however, since there is no advantage to applying excessive amounts of this nutrient. If a soil test indicates that potash is lacking, choose a fertilizer containing potassium with zero or a very low percentage of nitrogen (the first number on a fertilizer bag) during the late summer or early fall because we are not trying to stimulate growth for the reasons discussed above. If a soil test calls for adding potassium, you can apply during late summer to early fall while the lawn is still growing. Very slow growth still occurs even though day lengths get shorter by late September and October. I am sure that you have probably noticed before that you do not have to mow your lawn as often as we move into October.
An important fact to consider if you bag your lawn clippings: The removal of grass clippings from lawns can severely deplete the soil of potassium. Grass leaves and stems contain very high levels of potassium. Keep in mind that when a lawn is mowed appropriately, it is better to leave clippings to decompose on the lawn as a good source of turf nutrients, including potassium. Clippings from a lawn that is mowed regularly have only a small role in the overall buildup of thatch in turfgrass.
Fall is the best time of the year to get your soil tested by the LSU AgCenter Soil Testing and Plant Analysis Lab.
Soil testing really is the first step to a beautiful lawn next spring and is the best way to determine exactly what your lawn needs to become thick and healthy. If you have not tested your soil in the past several years, do it now.
To test your soil, submit a pint of soil to the LSU AgCenter Extension Service office in your parish. The pint should be a composite of soil samples collected from several different areas in the lawn. You only need to go about 4 inches deep. Also, to simplify the soil sampling and submission process, there are pre-addressed submission boxes with sampling instructions at several garden centers throughout the state. There is a small fee for testing.
The sample results will be sent to your home mailbox and email in less than two weeks. An LSU AgCenter extension agent can help you interpret the results from the soil sample. The results may indicate that lime is needed to increase soil pH. If so, fall and winter are good times to apply lime because it takes several months to activate in the soil. Elemental sulfur may be recommended to reduce soil pH in alkaline soils.
The best way to cut down on winter weed problems is to get your lawn thick and healthy during the spring and summer months. If your lawn struggled during the growing months, inevitably it will be full of winter weeds next spring. Late summer/early fall is your first opportunity to reduce winter weed infestations with preemergence herbicides. Preemergence herbicides, such as prodiamine, pendimethalin, dithiopyr, isoxaben and indaziflam may be applied in mid-to-late September to help manage the first flush of winter weeds like annual bluegrass, chickweed and lawn burweed. Consider reapplication in early November. These herbicides work prior to the emergence of the weeds, so timing the application before the weeds germinate is critical. Atrazine can be applied on most southern lawns for annual bluegrass and broadleaf weeds in October except for bermudagrass. Atrazine could be applied on bermudagrass after the bermudagrass is dormant. MSM (metsulfuron) can be highly effective postemergence on broadleaf weeds, such as white clover and lawn burweed. Lawn burweed, or “sticker weed,” is a winter annual that germinates in October and grows all winter long. Next April, lawn burweed produces the burs that are capsules that contain burweed seed. To avoid the stickers in the spring, you must treat lawn burweed during fall and winter.
Ron Strahan, Ph.D.
Associate Professor, LSU AgCenter
Weed Scientist and Turfgrass Specialist
Laurel wilt is a devastating disease of woody trees in the Lauraceae family. Trees currently susceptible to laurel wilt include avocado, California laurel, camphor tree, pondberry, pondspice, redbay, sassafras, swampbay and spicebush.
Laurel wilt was first confirmed in the state in 2014 on mature sassafras trees in Union Parish. Since then, the disease has spread to Beauregard, Bienville, Claiborne, Grant, Lincoln, Natchitoches, Ouachita, Rapides, Sabine, Vernon and Winn parishes. The disease is caused by a fungus called Raffaelea lauricola that clogs the vascular (xylem channels) system of the tree and interrupts the water supply. As a result, the affected tree wilts and eventually dies. Initial symptoms of laurel wilt are rapid wilting and drooping (flagging) of leaves. As the disease progresses, infected trees exhibit reddish to purplish brown discoloration of foliage and the entire canopy turns brown. Brown leaves do not defoliate immediately and tend to remain attached to the branches for a period of one year or more in the case of redbay trees, but brown leaves drop readily in other host trees. Removal of bark from infected trees reveals discoloration of sapwood.
The fungus is carried by the invasive redbay ambrosia beetle (Xyleborus glabratus) from infected to healthy trees. The pathogen also may spread from infected trees to neighboring healthy trees through grafting roots. Both the beetle and fungus also may spread to new locations indirectly when people move infested firewood from areas where laurel wilt and redbay ambrosia beetles are prevalent. Redbay ambrosia beetles are brown to black in color and very small (2 mm) in size. Initially, the redbay ambrosia beetles may attack the branches, and the infested trees may not look wilted. Later, the trees start to wilt, and toothpick-like tubes of fine sawdust produced by ambrosia beetles can be seen on the trunk. The sawdust toothpick-like tubes may easily wash away with rainwater and may not be present on infected trees after a downpour.
Rapid and early disease detection and removal of infective trees is the most effective management strategy to combat laurel wilt. After removal, burn the diseased trees or dispose of them properly to prevent the further disease and beetle spread. Avoid moving firewood from areas where laurel wilt and redbay ambrosia beetles are prevalent or known to occur. When it comes to firewood, remember to buy local and burn local!
Early symptoms of laurel wilt can be easily misdiagnosed with the damage caused the black twig borer (Xylosandrus compactus). The black twig borer attacks small diameter branches and causes death (flagging) of infested branches. If you notice symptoms of laurel wilt on susceptible host trees listed above, please contact Dr. Raj Singh at 225-578-4562 or email firstname.lastname@example.org
Raj Singh, D.P.M
“The Plant Doctor”
Associate Professor/Horticulture Pathology Extension Specialist
Director, Plant Diagnostic Center