Gardenia & Hydrangea

Karen Cambre, Sharpe, Kenneth W.

Thrips_on_Gardenia_lgjpgNews article for May 7, 2018

Gardenias are in full bloom, and you can smell their fragrance before you see their mass of showy white blooms.

This is a classical old Southern garden plant that produces very fragrant summer flowers. You may know gardenias as cape jasmine. They are consistently in bloom for Mother’s Day.

Gardenias prefer full sun to partial shade and like a moist but well-drained, fertile soil.

Older varieties and plantings of gardenias can turn into small trees and exceed 8’ x 8’. The variety Frostproof is a Louisiana Super Plant selection. It has been developed to have better cold tolerance, and it becomes fully mature at 3-4 feet tall and 4 feet wide. Like other varieties, Frostproof has a huge flush of blooms in May but will also sporadically bloom throughout the summer.

If your gardenia blooms are turning brown very quickly, check the inside of the blooms for thrips. Thrips are small, slender, slightly tan insects that you can see by the hundreds feeding inside blooms. You can use an insecticide such as Malathion, Orthene or Acephate to help control thrips. This insecticide application would also help control aphids. Aphids are soft-bodied sucking insects that suck plant juices from the underside of leaves and cause sooty mold. Sooty mold is prevalent in gardenias and shows up as a crusty black, unattractive flaky film that covers the leaves. Sooty mold lives on the sugars secreted by the aphids. If you control aphids, you will not have sooty mold.



Another reliable Mother’s Day blooming plant is hydrangea. So reliable that I see a lot of potted hydrangeas in the nurseries this time of year packaged with bows especially for Mother’s Day gifts.

If you received one as a gift, you will want to plant it so you can enjoy its beauty for years to come. Hydrangea is another Old South garden specimen that grows well if you put it in the right place. They like partial sun to shade in a fertile soil that is moist but well drained. They do well in a place with morning sun and afternoon shade.

Flower color for most hydrangeas is determined by the pH of the soil. Acid soils will produce blue flowers, and alkaline soils will produce pink flowers. If you want to change the flower color, change the soil pH.

If you have blue flowers but want them to be pink, add 2 to 3 tablespoons of lime around the plant and repeat in 6 months. To change from pink to blue, add about ½ cup of aluminum sulfate around plants and repeat in 6 months. Neither color change will be immediate, but you should see the difference by next year.

Both hydrangeas and gardenias are what we call summer-flowering plants. If they need to pruned, you want to prune as soon after blooming as possible. This will allow for normal flower bud formation for next year’s blooms. If you wait until late summer or fall to prune, you will cut off all of your blooms for next year. Routine pruning is not necessary. Use pruning as a way to remove weak and dead wood. If you need size reduction, cut back no more than one-half of the green growth. New green shoots will develop, and flowers should be produced for next year.

For more information on these or related topics, contact Kenny at 225-686-3020 or visit our website at

5/9/2018 6:30:18 PM
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