Gardenia flowers. (Photo by Allen Owings. Click on photo to download image.)

News Release Distributed 05/1812

By LSU AgCenter Horticulturists Dan Gill, Kyle Huffstickler and Allen Owings

Gardenias are blooming in Louisiana landscapes now.

Known as cape jasmine to some Southern gardeners, gardenias are one of the most widely planted landscape shrubs in Louisiana. The LSU AgCenter has recommended several species and varieties for landscape use, and they continue to be very popular among home gardeners.

When you select gardenia varieties, look for the better performers. The best currently available now is the variety Frostproof. It was a designated a Louisiana Super Plant in 2011. Other good choices include the new Jubilation variety in the Southern Living plant program along with Mystery and August Beauty, which are older varieties. And one more to consider is the daisy gardenia.

Although popular, gardenias regularly are plagued with problems. This is especially true with dwarf gardenias, but other varieties have their difficulties, too.

A planting group may do very well, with no plants lost the first year. Or a planting may do poorly, and all plants are lost in the first year. Sometimes a few plants in a grouping may die each year, so after two to four years, no living plants remain.

We have a few guidelines to consider that can improve gardenia landscape performance.

Soil pH is important for gardenias and other plants. Gardenias belong to the “acid-loving” group of ornamental plants. This means they prefer low soil pH. The recommended soil pH for gardenias is 5.0-5.5. This is similar to what azaleas, camellias and blueberries also require. Plants may do fine at a soil pH in the upper 5s to low 6s, but adverse nutrient availability and root growth problems occur when soil pH climbs above 6.5.

We all need to know the soil pH in our landscape beds. Adjust soil pH by lowering with sulfur or raising with dolomitic lime. Always follow recommendations of a soil test, which you can get for a fee from the LSU AgCenter. Contact your AgCenter parish office or go to the soil lab page.

As with many other shrubs, roses and flowers, improving internal drainage and building raised beds are usually necessary when planting gardenias in Louisiana. Our heavy rainfall in short periods of time saturates landscape bed soil and will lead to root rot issues.

You can lessen this problem by making a raised bed 6-8 inches tall prior to planting. This helps prevent root rots that may occur if irrigation is not properly managed and/or if beds aren’t properly prepared and provided with adequate drainage.

When you plant, don’t plant gardenias too deep. Watch your planting depth and be careful about piling mulch around the base of the stems, which simulates planting too deep. Plant gardenias slightly higher than how the plants were growing in the original containers. Allow for soil settling. Be sure to “water in” the plants during the backfill process. Avoid over-mulching. Mulch with pine straw to a depth of 2-3 inches.

A slightly stressed gardenia will decline rapidly when over-watered. At the same time, we need to make sure plants are not under-watered. Uniformity in soil moisture is the key to success with gardenias, so monitor soil moisture closely between rains. Once-a-week irrigation should be sufficient.

Make sure water distribution is uniform. Water quality also can play a role in gardenia performance in the landscape. Irrigate slowly, deeply and infrequently rather than quickly, shallowly and often. Once root rot occurs, plants can usually not overcome the problem, and homeowners have limited fungicide options for control.

Gardenias need a moderate amount of nitrogen fertilizer but also are harmed when nitrogen is applied excessively. Apply a recommended slow-release fertilizer shortly after spring bloom. This should handle nitrogen needs for that growing season.

Gardenias also are frequently fertilized with foliar or soil applications of iron, such as Ironite. This basically is offsetting a slightly higher-than-recommended pH that is inhibiting iron uptake from the soil.

Gardenias are not difficult plants to grow. We just need to follow these recommendations to improve their landscape performance.