Summary: Below is a series of Gardenia pests and disease problems homeowners may experience.
Gardenia Leaves Turning Yellow
The Gardenia plant (Gardenia jasminoides) produces fragrant flowers and handsome foliage making it a great addition to any garden. However, maintaining gardenias is not an easy task and mishandling would put it at risk of dying.
Yellowing and dropping of Gardenia leaves have several possibilities… from a nutritional deficiency, low humidity and overwatering.
Yellowing Leaves From Nutritional Deficiency
1 – If your plant has a magnesium or iron deficiency, growth may become retarded along as the leaves turn yellow or discolored.
2 – Gardenias in need of fertilizing, will exhibit symptoms of no buds or dropping buds, gardenia yellow leaves spots or yellowing at outer leaf edges and moving inwards, pale bleached look, dropping older leaves.
Same as above – If there are no flowers or buds – feed the acid-loving plants with an acid gardenia fertilizer. No feeding while the tree blooms or during winter.
Massive Leaf Drop and Yellowing Leaves
Yellow leaves on gardenia in mass followed my leaves dropping, the problem often is watering – Too Much water.
If leaf curl, gardenia leaves turning brown, dieback occurs and the soil is constantly wet. The plant should be removed from the pot immediately. Check the root ball for health, make sure pot drainage holes are not plugged.
Checking The Roots:
- White healthy looking roots – remove all bad foliage, place back in the pot and fix watering issues or repot into fresh new soil.
- Roots damaged and partially brown – remove bad roots, repot in fresh soil
- Roots mushy and brown – discard plant
Gardenia Leaves Yellowing From Low Humidity
The symptoms of low humidity show up as: flower buds dropping, leaf tips turning brown, yellowing foliage, gardenia flowers turn brown.
Place the potted gardenia in a tray or bed of moist pebbles. DO NOT allow the pot and roots to sit in water. Spray/mist once or twice per day. In winter use a humidifier.
Gardenia Bud Drop
Question: The buds on my gardenia plant get about ready to open, then start to turn brown. What can I do to make them bloom?
Answer: This trouble is referred to as bud drop. The proper culture to prevent bud drop is difficult in a house and often occurs in spite of all precautions in a home greenhouse.
Frequent overhead watering after the buds are set may cause them to drop, but lack of sunlight is the chief cause of bud drop. With a uniform temperature of 60 to 62 degrees, good light, and high humidity, the chances of bud drop are slight.
A pot-grown gardenia should have a regular application of one ounce of iron sulfate to two gallons of water at least once a month to maintain correct soil acidity.
An alkaline soil condition will prevent the buds from opening and is one cause of bud drop. If unsure of the soil pH, gardeners usually conduct a soil test.
New Plant Bud Drop
If the buds on a new gardenia plant turn to black and drop off the issue could be all environmental. Plants moving from a nursery environment to a garden center and then to the home could “shock” the plant as it is acclimating to new surroundings: low light, warm temperatures in the home, low humidity can all contribute to bud drop.
Spray-mist on a daily basis, place plant on a tray of pebbles to increase humidity.
Question: I have three large gardenia bushes, about 12 years old. This year there is black mold on the leaves of new growth. How can I rid the bushes of it? CAE, Texas
Answer: One “type” of sooty mold is caused by an airborne fungi. These Gardenia pests usually appear when plants are chilled or wet frequently and not properly ventilated. Better light, more air, and keeping the foliage dry when watering is the best preventative. A light spray using oil emulsion such as Volck diluted one to 75 will destroy sooty mold fungi on gardenia bushes.
Question: What causes a sooty, black film on the leaf surface of gardenias?
Syringe plants with water a few days after to wash off the dirty film. Privet and lilac are also attacked by these pests. Other pests that may infest the gardenia plant include spider mites and aphids.
Related Reading: Getting Rid Of Sticky Leaves On Houseplants
Water & Spraying
Question: I was told that a gardenia plant needs to be watered every other day and sprayed once a week with malathion. What fertilizer suits it best and how much should be applied and how often? Should it get sun or shade? TZ, Mexico
Answer: The gardenia is a sun lover but some shade during the hottest part of the day is not harmful. It needs water often enough to keep it from getting really dry when growth is active but probably not every other day.
A weekly forceful spray of water with occasional sprays of malathion should keep the plant clean and free of insects. If your plant is outdoors, a 2-inch layer of peat moss and rotted cow manure over a well-drained soil is advantageous. For healthy gardenia plants, keep the soil moist but don’t over water to avoid root rot.
If confined in a container, a 5-10-5 slow-release fertilizer could be used either dry at the rate of a level teaspoonful to a 6-inch pot or as a liquid at the rate of 2 teaspoonfuls stirred in one gallon of water. Food may be given the plant about every three weeks when growth is active.
Question: Could you tell me how to start a new gardenia from an old one?
Answer: Tip cuttings three or four inches long are taken late in the winter and rooted in a mixture of sand and peat. Insert unrooted cuttings in 2-1/2-inch pots, and give them a bottom temperature of 70 to 75 degrees.
If kept moist and in an atmosphere that is not dry, the cuttings will root in about eight weeks.
Normally, gardenias grown outside are attacked by only a few insects and one serious disease.
When gardenias are attacked by root-knot nematodes, the leaves become chlorotic.
These microscopic worms produce characteristic galls or swellings on the roots. Prevention consists of soil sterilization before planting but using steam or chemicals.
Care should be taken when using any chemical materials since they will kill plants (people too) when used too close. Once the plants are infested they should be destroyed as there is no cure.
The scale insect is the most common pests attacking gardenias grown outdoors.
Thrips can also be bothersome, especially when gardenias are grown near a field of weeds.
Black scale can be a real pest. Each scale is about the size of a small split pea, dark brown to black and nearly hemispherical with a conspicuous H-shaped marking on the back.
The honeydew secreted attracts fungi which in turn give the leaves and stems a black, sooty appearance. This also attracts ants which help spread the scale.
In Florida and the Southeast the scale pest is the Florida waxscale, reddish or brown and the size of a pinhead.
Orthezia sometimes attacks gardenias grown outdoors; they are small, long and white, with long stripes on their backs. You will need a hand lens to see them.
All the scales are sap-sucking and some inject a poison. The soft brown scale can be a serious pest at times. too. It is greenish brown, oval-shaped, rather flat and about 1/8 inch long. It infests leaves and limbs and produces a honeydew as does the black scale.
The treatment for all scale is a summer oil spray applied at two-week intervals using a 2 percent oil, Malathion can be used as well but I prefer oil.
Water plants well one half-hour before spraying and again syringe with water an hour after spraying.
Thrips and the tobacco thrip are also common gardenia pests. Injury is manifested by a silvering of the leaf because the thrips suck the plant juices. You will need a hand lens to see them on the underside of the leaves as they are very small flying insects.
Clean up all weeds which harbor them.
The citrus mealybug is usually found on greenhouse gardenias, but sometimes attacks those grown outside.
A hard, sharp syringing with a small spray of water usually keeps them under control in many vegetable gardens. Otherwise, use a 2% percent summer oil and a teaspoonful of Malathion to each gallon of water.
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Whiteflies are quite small, about 1/16 inch long. The adults are pure white and when disturbed fly away from the underside of the leaf where they feed. The larvae look like very small mealy bugs. Both adults and immature stages are found together. For outdoor control use organic neem essential oil sprays (natural) or Malathion (chemical).
Red Spider Mites
Tiny red plant spider mites sometimes attack the plants in late summer, especially when the air gets – hot and dry. You will need a hand lens to see the reddish spider mites which can be controlled by regular hard syringing with cold water.
Do not become alarmed by our mention of all these insects – your plants may never be attacked by any of them but it is best to be aware of them if they do.
Gardenia Pest Management
There are plenty of natural ways you can use to get rid of gardenia pests. One of the most effective and safest ways is by making use of diatomaceous earth or food grade DE. This natural pest control substance help eradicate a wide array of insects.
Some essential oils such as neem oil help solve common pest problems. Peppermint oil wards off squash bugs, parasitic wasps, mites, tomato hornworm caterpillars, beetles and more. On the other hand, cedarwood, hyssop and pine essential oils keep slugs and snails away from your gardenia plants.
Introduction of beneficial insects that feed on vegetable garden pests will also help solve the infestation.
The one disease most often found is phomopsis canker, a fungus disease (ficus trees get this as well).
The first symptom of this disease will be a shrinking of the stem at the soil line. This gradually enlarges and the whole stem swells and becomes rough and cracked.
The leaves become pale green, then yellow and many fall. Since the disease enters plants only through wounds, use all possible care not to injure the stem when planting or pruning. There is no known cure so dig and destroy (burning is best) infected plants.