Herb Gardening Louisiana Style

The steamy climate of the deep South–hot, wet, stick-to-your-back humid, with winters so mild they stretch the definition of the word–demands its own approach to herb gardening. This area of the United States is in many respects a gardener’s paradise: the rainfall, humidity, and fertile soil ensure dense, lushly green, sometimes junglelike vegetation, and the gardener often spends more time controlling growth than in encouraging it. But these very conditions, so unlike the arid, rocky slopes of the Mediterranean where so many culinary herbs originated, present a formidable challenge to the would-be herb gardener. More and more people are now taking up this challenge–and learning a lot along the way.

In nineteenth-century Louisiana, herbs were commonly interplanted with vegetables in kitchen gardens. As plantations disappeared and the population became more urban, such gardens became scarce. Only in recent years have Louisianians begun planting home herb gardens in great numbers; evidence of this interest can be seen in the recent founding in Baton Rouge and New Orleans of the two newest chapters of The Herb Society of America. Herbs are claiming more prominence in nurseries as public demand for them increases, and this renewed interest in herbs is the main impetus behind a showcase public garden in Baton Rouge that demonstrates on a large scale how herbs can be grown in this climate.

The Burden Research Plantation comprises 450 acres in the heart of Baton Rouge. Once a working plantation, the land was donated to Louisiana State University (LSU) by the family of the retired landscape architect Steele Burden. The original estate, Windrush, was a wedding gift to Steele Burden’s grandmother about the time of the Civil War, and his parents kept it as a retreat, riding uptown in their buggy to spend the weekends there. Steele and his sister, Ione, turned the estate over to the university in 1972 with the stipulation that it be maintained for horticultural research.

Today, the Burden plantation is a fascinating place to visit for many reasons, not the least of which is its Rural Life Museum, one of the finest outdoor folk museums in the United States. Old Civil War-era buildings from plantations around the region have been saved from destruction and preserved here to house eclectic collections–from spinning wheels to horse-drawn hearses–of artifacts related to life in eighteenth- and nineteenth-century rural Louisiana.

Burden is also a state agricultural experiment station devoted to ornamental horticulture. In the surrounding acreage, many research projects are conducted, and the public garden areas are oases of beauty and serenity within the capital city. Many herb varieties and ornamentals are trialed here for the state nursery industry to determine which plants do well in this hot, wet climate and how best to grow them. The gardens also allow residents and visitors to see how many herbs, roses, and other ornamental plants look as they grow to maturity in the landscape. Demonstrating to homeowners how they can incorporate ornamental edibles into their landscapes is part of the mission of the public gardens, according to Peggy Reed, the university research associate who maintains the large and graceful herb garden.

The herbs were first planted as an exhibition garden late in 1987 in anticipation of the annual meeting in Baton Rouge the following summer of the International Herb Association (then the International Herb Growers and Marketers Association). The garden has been expanded several times since, and despite funding cutbacks it continues to grow, thanks in part to the enthusiasm and help of local Herb Society of America members.

The herb garden is laid out at one end of a large turfgrass section bord­ered on its sides by perennial beds. About 150 feet long, it consists of three large raised beds framed by landscape timbers and separated by heavily mulched pathways. Here are more than 100 different herb varieties, including many that over time have proven their adaptability to Louisiana soil and climatic conditions.

As can be seen at Burden, many herbs thrive in the moist heat despite the common notion that the South is not hospitable territory for herbs. Gardeners from elsewhere can only marvel at Burden’s large clumps of lemongrass, chest-high basils, splashy ornamental salvias and bushes of pineapple sage, the showy candlestick tree (Cassia alata), rosemary that blooms through the winter, Red Shield hibiscus that Creole chefs use to color and flavor sauces, the wonderfully fragrant butterfly ginger lily, both bay laurel (Laurus nobilis) and the native red bay (Persea borbonia), henna, and vetiver.

Though there are many success stories here, some of the most common and most useful culinary herbs are very difficult or impossible to grow, primarily because of the dampness. We talked at length with Peggy Reed about herb gardening here in Bayou Country: cultivation practices, ways to cope with the sogginess, and specific varieties and cultivars that perform well here. We think that gardeners from other Southern areas might benefit from some of the work going on in this research setting.

Conditions and Solutions

Baton Rouge, straddling USDA hardiness zones 8 and 9 about an hour’s drive northwest of New Orleans, averages more than 60 inches of rain a year, with 65 to 90 percent relative humidity. Summers are hot and sticky, and winter temperatures seldom dip below about 40°F, with only a handful of freezing days. Louisiana’s weather patterns are heavily influenced by its proximity to the Gulf of Mexico; the fronts that come in off the gulf usually carry a heavy load of moisture that is then dumped on the coastal and inland areas, sometimes for days at a time.

The soil at Burden, with a pH of 5.5 to 6, is more acidic than most herbs prefer, so limestone is worked in with every planting. The silt loam topsoil is shallow, in some spots only 4 to 6 inches deep. Beneath it, a thick layer of clay subsoil holds the moisture in place, resulting in poor drainage that is the herb gardener’s single biggest problem, according to Peggy.

To improve the drainage, Peggy uses readily available local materials for both amendments and mulch. These include sand, pine bark, rice hulls, pecan shells, bagasse (crushed sugarcane residue from sugar production), horse manure, and wood shavings, all of which she usually composts before applying them. The pathways are heavily mulched with bark, leaves, and chipped tree trimmings. Because organic matter decomposes rapidly in this climate, adding more materials to the soil and to the mulch must be ongoing.

Mulching prevents wet soil from splashing up onto the leaves of plants and spreading soil-borne disease organisms such as rhizoctonia and fusarium, which can be serious, even lethal for lavender, rosemary, basil, and others. A layer 2 to 4 inches thick also helps keep weeds and other invasive plants in check. Around the Mediterranean herbs that are the trickiest to grow here, such as lavender and garden sage, Peggy spreads a light-colored gravel and sand mulch, which reflects light into the interior of the plants, keeping them drier. That’s a tip from Art Tucker, a botanist at Delaware State University who has done considerable research into herb cultivation. Peggy sometimes mulches with roadbed limestone, which is also light in color but chunkier than gravel; it gives the Mediterranean herbs the extra lime boost they prefer.

Raised beds are an invaluable tool for improving drainage. Adding amendments over a long period essentially ­creates new soil, thus deepening the topsoil layer. To prevent her hard work from being washed away by heavy rains, Peggy has framed her raised beds with landscape timbers, which also help keep the greedier plants within bounds. At the edges of the beds, creeping ground covers such as catmint, dianthus, golden and Greek oregano, marjoram, and lemon thyme soften the edges visually while serving as a “living mulch” and holding the soil in place.

The herb garden is in full sun. In addition to limestone, newly planted herbs receive an application of slow-release fertilizer. Peggy topdresses with composted horse manure occasionally during the growing season.

She gives each herb plenty of growing space–especially important in this climate to encourage air circulation through the interior of the plants. Regular pinching, clipping, and thinning also do much to discourage fungal disease while promoting shapelier plants. Peggy removes the lower leaves of lavender and rosemary, and she is ruthless when she trims back the mints, the most invasive plants in the garden.

Insects, which don’t die off in the mild winters, are often a gardening problem in the South but not at the Burden herb garden. No pesticides are used here, and Peggy credits the aromatic qualities of the herbs for the lack of any serious insect problems.

Peggy waters when she sets plants in and during the summer if they look as though they’re wilting, but otherwise she leaves them alone. Many businesses in the area use automatically timed irrigation systems to water their seasonal color beds, which subsequently just rot out. “We’re really still learning the cultural practices needed to keep down the fungal problems here, and it’s important not to add extra moisture,” Peggy says. She advises watering early in the day to give the plants plenty of time to dry out before nightfall. At one point, Peggy tried a misting system but found that it contributed to disease problems; now she waters with a hose only around the base of the plants.

Newcomers to gardening in the deep South must go through a shift in their perceptions of the seasons. Fall does not herald the end of the growing season as it does in many other parts of the United States. It is in midsummer, when heat and humidity peak, that plants go dormant or just give out (“They actually steam to death,” Peggy says) and gardeners head indoors to air conditioning. Autumn’s shorter, cooler days provide a long and pleasant season for planting, much like a second spring. Most of the major herb planting at Burden is done in September. Except during the occasional harsh winter that claims a few victims, most plants grow on through the winter, blooming long past the time when Northern gardens have gone to bed. The Burden gardens get little rest.

Success Stories

Knowing which plants and varieties perform well in a given climate can save a lot of disappointment, and LSU’s research garden provides that information for area residents. Lavender, for example, is tough to grow here, but Peggy Reed can tell gardeners which varieties are most likely to succeed. We asked her to recommend some species and varieties of herbs that have been standout performers in the Burden herb garden. Here’s her report.

Sage. Because garden sage (Salvia officinalis) needs drier conditions than Louisiana can provide, it is generally grown here only as a cool-season annual. However, the cultivar Berggarten holds up very well when grown as a perennial. It is an attractive plant with broad, pebbly leaves of good flavor. Pineapple sage (S. elegans), with its fresh pineapple scent and brilliant red flowers, does extremely well here.

The ornamental salvias are some of the showiest plants in the Burden garden. Peggy grows many kinds, always searching for new ones, and has introduced several to area gardeners. Among her favorites are the yellow-flowered forsythia sage (S. madrensis); white Texas sage (S. coccinea ‘Alba’); fall-blooming, purple-flowered Mexican bush sage (S. leucantha), which she likes to plant alongside African Blue basil; hot pink rosebud sage (S. involucrata); and bog sage (S. uliginosa), which has pretty sky blue flowers but is invasive. Two hybrids that Peggy grows and admires are Indigo Spires and Purple Majesty, both of which have blue to purple flowers. She is now trialing a promising new hybrid of autumn sage (S. greggii ¥ microphylla ‘Cherry Chief’) and Galeana red sage (S. oresbia), as well as others.

Rosemary. Among the upright forms of rosemary (Rosmarinus officinalis), Peggy has been successful with Logee’s Blue, Hill Hardy, and Arp, but she doesn’t hesitate to name her favorite: Tuscan Blue, a vigorous grower with a mild, fresh scent and blue flowers. The only prostrate rosemary that has done well for her is Santa Barbara, a lovely ground cover with arching stems covered almost year round with pale blue flowers.

Lavender. At Burden, lavenders are grown in clay pots to give them better drainage than they would have if grown in the ground; during long rainy spells, Peggy moves the pots into a greenhouse to give the plants’ roots a chance to dry out. Because most succumb by midsummer no matter what treatment they get, she grows them as annuals. Two lavenders have performed best here: gray-leaved fringed or French lavender (Lavandula dentata) and L. multifida ‘Fernleaf’, whose camphorous fragrance doesn’t appeal to some diehard lavender fans but which is nonetheless an ornamental plant in the garden. Peggy also has high hopes for a recently acquired Spanish lavender (L. stoechas), with its beautiful purple butterfly-shaped flowers.

Basil. Basil is the main warm-weather annual herb planted at Burden each April. It thrives in the fields, where studies are conducted on the essential oil production of field-grown cultivars, as well as in in the herb garden, where it lends its ornamental qualities. Peggy likes to use the purple-leaved varieties to contrast with gray-foliaged plants such as Powis Castle artemisia.

It’s almost impossible to delay flowering in most basils in the heat of a Southern summer; as they’re generally grown for their leaf production, which stops as the plant goes into bloom, this trait is a frustrating one for the gardener. Two vigorous basils grown in quantity at Burden have the advantage of flowering very late, if at all: the small-leaved Ocimum basilicum ‘Aussie Sweet’ and slightly larger-leaved O. b. ‘Greek Columnar’, both with a pleasant flavor; Peggy propagates them from cuttings. Another favorite at Burden is Mrs. Burns’ Lemon, which outperforms regular lemon basil (O. citriodorum) here and reseeds prolifically. Another standout is a huge and fragrant shrub of tree basil (O. gratissimum).

Mint marigolds. Tarragon won’t tolerate the humidity here, and Peggy doesn’t bother trying to grow it. Many cooks consider Mexican mint marigold (Tagetes lucida), which does thrive in moist heat, a good substitute for tarragon in the kitchen. Peggy doesn’t agree about the taste, but she prizes the marigold for its fragrance and bright golden yellow flowers in the autumn. She recently added another perennial mint marigold, T. lemonii, to the beds as well.

Thymes. Both upright and creeping thymes grow in the Burden herb garden, but few have the vigor that they might have in drier climates. Lemon thyme and caraway thyme perform well, though, as does common thyme. Peggy grows them with the other Mediterranean plants that she pampers a bit with light-colored gravel, extra sand, and additional lime.

Garlic. Garlic is essential to Cajun cuisine, but the familiar Allium sativum often rots in the ground. After trying many varieties of garlic, Peggy has settled on elephant garlic (A. ampeloprasum), which has huge bulbs and a mild, sweet flavor and holds up well in the garden. In the kitchen, she compensates for its mildness by doubling the amount of garlic called for in a recipe.

Weaving through the Burden herb garden are many other herbs. Borders of society garlic, lamb’s-ears, and parsley frame the plantings. The beds include plants for crafts, such as globe amaranth, celosia, yarrow (including the brightly colored Paprika), and Gold Sticks tansy, which stays a foot or two shorter than the species; plants to attract butterflies and hummingbirds, including agastaches, monardas, and large buddleia shrubs at the rear of the garden; natives, such as Joe-Pye-weed, purple coneflower, and asclepias; and edible flowers, such as calendulas, nasturtiums, and violets. Interplanted with the herbs are small ornamental peppers in a rainbow of colors, and daylilies and Chinese chives show off along the length of the beds in midsummer.

“There are so many herbal plants that could do well in this region. Since herbs are so naturally disease- and pest-free, they are very valuable plants. We feel that a large part of our role here is to show people what they could be growing and to work with the nurserymen to make them available,” Peggy says.

The Burden garden is intended to be a learning experience, but it is also a tranquil retreat. Elsewhere on the grounds are other sunny and shady gardens gracefully punctuated by bronze and marble statuary, walkways, and ponds. An All-America Selections rose garden showcases 1500 mature plants. Varieties of crape myrtles, azaleas, and camellias that were used in nineteenth-century landscaping are abundant, helping Burden retain the appearance of an old Southern plantation.

The Herb Companion’s associate editor, Kathleen Halloran, spent some time recently in Louisiana looking at beautiful gardens, eating great food, and sipping an occasional mint julep in the spirit of herbal research. In the April/May issue, she’ll report on how the area’s professional chefs team up with herb gardeners to host a sumptuous annual culinary herb festival in Baton Rouge.

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