Landscape plantings of gardenias in the late fall and winter may appear less vigorous and poorer growing than in spring and summer. (Photo by Allen Owings)

News Release Distributed 01/16/15

By Allen Owings
LSU AgCenter horticulturist

HAMMOND, La. – One of the most widely planted landscape shrubs in Louisiana is the gardenia. Many times from the late fall through winter, you may see gardenias with yellow foliage and “poor-looking” growth. This is more of an “end-of-the-growing-season” look when old leaves are being lost and new foliage is preparing for spring emergence.

However, you should consider these key factors to optimize the appearance of your gardenias.

Gardenias occasionally are prone to disease problems. This is typically due to improper or poor management practices in the landscape. A planting may do very well the first year with no plants being lost. Or the opposite might happen – a planting may do poorly with all plants being lost. Sometimes a few plants in a grouping die each year; thus, after two to four years, you have no living plants remaining.

Here are a few points for improving gardenia performance.

Soil pH is an important consideration for all gardenias. The recommended soil pH is 5.0-5.5. This is considered moderately to strongly acid. Adverse nutrient availability and root growth problems occur when soil pH climbs above 6.0 and become a major problem at soil pH above 6.5

Proper bed preparation with good drainage is needed when planting gardenias. Improving internal drainage and constructing raised beds are always necessary when planting in Louisiana. Root rots will occur if irrigation is not properly managed or adequate bed preparation or soil drainage is not provided.

Monitor planting depth when adding gardenias to the landscape. Be careful about piling mulch around the base of the stems, which simulates planting too deep. The root ball should be a little higher than the soil line when planted in the ground. Allow for soil settling.

Managing irrigation properly is important in all landscape beds, but it is critical for gardenias and azaleas. Not too wet; not too dry – that’s what’s needed. Soil moisture uniformity is best. Sometimes this is hard to achieve during wet winters and dry summers. A slightly stressed gardenia will decline rapidly when overwatered. Watering once a week during late spring through midfall should be sufficient if rainfall is lacking.

Fertilization is required for good gardenia growth. Plants need nitrogen, and iron is a requirement because these are acid soil loving plants. Gardenias need a moderate amount of nitrogen fertilizer but can be harmed when nitrogen is applied excessively, so apply a slow-release fertilizer shortly after spring bloom. This should handle nitrogen needs for that growing season. Foliar or soil applications of fertilizer with iron, such as Ironite, can help prevent yellowing of leaves – known as interveinal chlorosis – and other nutrient deficiencies caused by high soil pH, especially with dwarf gardenias.

Recommended gardenia varieties for Louisiana landscapes include the widely popular Louisiana Super Plant FrostProof and the well-known Daisy and August Beauty varieties. Others include new varieties like Jubilation and Scentsation, both of which are included in the Southern Living Plant Collection. These are good plants to start with if you’re considering gardenias for your landscape.

You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.