Gardens

Fragrant Exotic Gardenias
Few things are more appealing than the fragrance of gardenia blossoms on a warm summer night.

by Sid Mullis

The fresh fragrance of gardenias carried on a cool breeze is a hallmark of summertime in Augusta. But the elegant flowers are popular in local landscapes not just because of their calming aroma. Gardenias make good plants for use as free-standing specimens, mass plantings, screens, borders, hedges or ground covers.

Like many of our favorite exotic and native plants, gardenias have an interesting history. The flower is native to China and was enjoyed by the Chinese for more than 1,000 years before Westerners discovered gardenias in the 18th century.

GARDENIA HISTORY
The plant was named after Alexander Garden who came to the American colonies in the early 1750s. Settling in Charles Town, S.C., he was a physician, planter and naturalist who knew the countryside and collected plants and animals for scientific study. Over the years, he befriended biologists William Bartram and John Ellis, supplying them with horticulture advice and plants. In 1761, when Ellis received a specimen of a remarkable new plant from China, he named it after his friend Dr. Garden.

The plant took Europe and the colonies by storm, gracing the bodices of chic gowns and floating in exotic cocktails. Nestled in cellophane-windowed boxes, the ivory flowers were expensive gifts from hopeful suitors and penitent lovers. Even American jazz singer Billie Holiday followed the elegant fashion by wearing gardenias in her hair while she performed.

SOIL PREPARATION

There are two main types of gardenias planted in Augusta: cape jasmine, or common gardenia, and the radicans, a dwarf variety with small leaves.

Gardenias thrive best in acidic, moist, well-drained soils high in organic matter. Although we don’t have highly organic soils in the Augusta area, you can easily compensate by adding compost. It is best to incorporate it in a bed as opposed to adding it to an individual planting hole.

Soil pH should be maintained between 5.5 and 6.5. Where the soil pH is above 7 (possibly at the foundation of a brick house), you can add aluminum sulfate to bring it down to a desirable range. The best way to tell is to take a soil sample to your local county extension office.

Fall or spring is the best time to plant gardenias. Plant them in light to moderate shade, preferably with minimum competition from tree roots. They also grow well in pots.

FERTILIZATION

Proper fertilization is important for gardenia growth and flower production. Use a complete fertilizer such as 10-10-10 or 16-4-8 in mid-March, an ideal time for the first application. If you have several in a bed, use about a half pound of fertilizer per 100 square feet or approximately one teaspoon per foot of height for each plant. Fertilizer amounts vary depending on the growth rate desired for the plants. Organic fertilizers such as cricket manure, fish emulsion and blood meal are also good options. Feed the shrubs again in late June to encourage extra flowers on ever bloomers or faster growth on young plants.

Do not fertilize gardenias in the fall. Doing so will stimulate tender growth, which may be killed or damaged by cold. Most gardenias are only hardy to horticulture zone 7b so they are susceptible to damage during a cold winter when the temperature drops below 15 degrees.

Sometimes plants will become yellow (chlorotic) due to a deficiency of one or more micronutrients, usually iron. This happens with those plants at the brick foundation where the soil pH is over 7. With iron deficiency, you will be able to see the green veins in the leaves. Iron deficiency can often be corrected by acidifying the soil with aluminum sulfate or by a foliar application of iron.

Keep in mind that some leaf yellowing (without the green veins) on older leaves is normal. This will usually occur in late winter or early spring before new growth begins and is typical of many broadleaf evergreens.

PRUNING

Gardenias don’t necessarily have to be pruned unless they out-grow their space. If pruning becomes necessary, do so after they have finished blooming since most varieties bloom on old wood. You can prune those that bloom on new wood in late winter to early spring. You may also prune to eliminate any diseased, damaged or straggly branches. “We always prune ours late summer or early fall,” adds Sue Wilson, a master gardener intern.

IRRIGATION

Gardenias are relatively drought tolerant but certainly do better with irrigation during periods of drought. Watering is important because it largely controls the number of flower buds that remain on a plant to maturity. If water stress occurs in a heavily budded plant, many buds will fall off before opening. Regular watering is necessary even after blooming to keep the plants in good condition and resistant to harsher winter weather. Wilson only waters her gardenias during a prolonged drought and when they looked stressed. “I normally hand-water my gardenias with a water hose when they need it,” she says.

INSECT CONTROL

A few insects and diseases can show up on your gardenias, but the number one nemesis is whiteflies, tiny insects that resemble gnats. When you shake a heavily infested plant, the air instantly fills with a white cloud of these insects. Whiteflies live on the underside of the leaves, where you will also find their eggs or egg casings. During late April or May, they will be active for about two to three weeks, lay their eggs and then disappear until the next generation hatches out in late July or August.

Labeled contact insecticides include products such as one percent horticultural oil, insecticidal soap and other insecticides containing the active ingredients pyrethrins, pyrethrums, resmethrins, cyfluthrin, bifenthrin and malathion. Good coverage with your spray underneath the leaves is critical. For organic control, use horticultural oils, insecticidal soaps and yellow sticky traps.

Other options for control are systemic insecticides, including acephate, imidacloprid and disulfoton. Acephate is commonly sold as Ortho Systemic Insect Spray. Disulfoton comes in a granular form that is sprinkled on the ground. Common brand names for this are Di-Syston and Bayer Advanced Rose and Flower Care. The Bayer product also contains fertilizer. Imidacloprid, sold as Bayer Advanced Tree and Shrub Insect Control, comes in a liquid that you mix with water and pour on the ground.

Acephate and disulfoton last for six weeks while imidacloprid should provide protection for up to 12 months. Even though acephate can last for six weeks, if whitefly populations have built up before your first spraying, you might need to follow it up with a second spraying about a week later for adequate control.

In sandier soils nematodes, microscopic worms that live in the soil and feed on plant roots, can cause gardenias to be stunted or even die. Although many kinds of nematodes affect gardenias, root-knot is the most common. Fortunately, the symptoms they cause are easily recognized: premature wilting, low vigor, thin canopy, and leaf and/or bloom loss under relatively mild stress. Roots infected by root-knot nematodes are swollen and gnarled. They often deteriorate prematurely because fungi readily attack the tender tissues that the plant produces in response to the infection.

According to Wilson, root rot caused by several different fungi can be a problem in poorly drained soils. “I have a drainage problem in one area where I had gardenias and I’ve had to replace two of them,” she says.

Your gardenias might also experience bud drop, when flower buds abort and drop off just before they open. Common causes include low humidity, overwatering, underwatering, insufficient light and high nighttime temperatures.

In general, gardenias are easy to grow and well worth the effort. They have been a staple in Southern landscapes for almost 250 years. And nothing whets our appetite for the outdoors more than the sweet smell of gardenia blossoms on a warm summer evening.

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