Saturday, January 15, 2011

On Gard!

No, the title is not a typo, I meant it that way. Just before going to the Green and Growin trade show this past week, one of my followers and I were discussing Gardenias.....yup professor it was you. Then at the trade show I had two more separate discussions about Gardenias and the trouble with growing them. I though this would be a good time to help some folks with this interesting, sometimes hard, fragrant plant.
Gardenia is a group of about 200 species of flowering plants that are in the Coffee family, Rubiaceae, native to the tropical and subtropical regions of Africa, southern Asia,and Oceania.
Gardenias were named by Carl Linnaeus after Dr. Alexander Garden (1730-1791), a Scottish-born American naturalist.
The common Gardenia that the majority of us know is Gardenia jasminoides also known as Cape Jasmine, Cape Jessamine and recently as Gardenia augusta. It attains a height of 2 to 6 feet and with its shiny green leaves and fragrant white Summer flowers, it is widely used in gardens in warm temperate and subtropical climates throughout the world.
The cultural requirements are acidic soil, having a PH of 5 to 6.5, ideally moist and high in organic matter, such as compost or ground bark, but make sure it is well drained. This is probably where most people go wrong, in their watering or soil media. The soil should be kept uniformly moist, but don’t overwater. High humidity is also essential to Gardenia care. Avoid misting the foliage, though, as leaf spot fungal problems will develop. I will discuss this later.
Their light requirements are going to depend on where you live and where you want to grow them. Plants prefer full sun if they are grown indoors; if grown outdoors for the Spring, Summer and early Fall, keep plants in partial shade. Partial shade being about 6 hours. They are listed for zones 8-10, if they are given a little bit of protection, I would say they could go to a 7.
When it comes to fertilizing, do it monthly between April and September with an acidic fertilizer, fish emulsion or blood meal. Do not fertilize Gardenias after September. Doing so will stimulate tender growth, which may be killed if/when the temperature drops below freezing. Gardenias are cold-sensitive and during severe Winters can be killed to the ground, often they regenerate in Spring. A very good layer of mulch can save the root zone if this should happen. Apply in Fall.
Prune shrubs after they have finished flowering to remove straggly branches and faded flowers. Pruning should be early enough to allow new growth to be at least 4 - 6 inches long by October 1. Pruning after October 1st decreases next year's blooms.
Occasionally there will be a problem with yellowing leaves. Yellowing of leaves may be due to a number of causes, such as insufficient light, over watering or poor drainage, soil temperature that is too low, nematode damage or disease. Some yellowing on older leaves is normal and may occur during the Fall and Winter months before new growth appears.
The biggest problem with Gardenias is their attractiveness to insects and other pests such as aphids, mealybugs, spider mites, thrips and scales. These can all be controlled with Horticultural Oils and Insecticidal Soaps. Please read all directions and make sure that Gardenias or the insect that you are targeting is listed on the label. The label is the law!
Diseases that affect Gardenias can also be numerous.
Sooty Mold
Is an organism that looks like a disease, often occurring on Gardenia foliage, turning it black. This black, smut-like substance does not injure foliage, but prevents sunlight from reaching the leaf, thereby reducing photosynthesis. The organism is not parasitic,meaning it does not actually live off the plant, but lives on honeydew secreted by sucking insects, such as aphids, scales, mealybugs and whiteflies that I listed above. Sooty mold can be managed best by controlling these insects.
You can learn more about Sooty Mold by reading my blog posting HERE
Other diseases that can occur are:
Rhizoctonia Leaf Spot
Leaves infected with this fungal leaf spot disease have tan to brown spots up to 1/4 inch in diameter. Spots are circular. The disease begins on the older leaves and spreads upward when the plants are watered excessively or when air circulates poorly because of overcrowding. Avoid wetting foliage when watering or misting, even if you are trying to raise the humidity level.
Powdery Mildew
This disease is characterized by white, powdery spots on leaves. Use a preventive fungicide to control.
One of the most common Gardenia diseases, canker is identifiable by a main stem swollen near or below the soil line. The bark becomes corky and contains numerous cracks in the cankered area. The stem above the canker is bright yellow in contrast to normal greenish white. If the humidity is high, a yellowish substance may be seen on the surface. Affected plants are stunted and die slowly. Destroy all diseased plants to prevent spread of this disease.
Propagation is rather easy. The most used method is by cuttings in moist soil, especially in warm Summer months.
Here in my Zone 8 Charleston, Gardenias bloom in mid-Spring to mid-Summer. The flowers are white, turning to creamy yellow as they age, and have a waxy feel.
This was from my plant this past Spring. The smell was amazing, such a shame my wife hates it!
I should mention, another one of the most irritating problems encountered with Gardenias is "Bud Drop". This is when the flower buds abort just before blooming. Common causes include low humidity, over-watering, under-watering, insufficient light, high temperatures, rapid temperature fluctuations, cold drafts or change in plant locations. So basically, Gardenias can be temperamental!
There are many cultivars available. But, lets say you are rather limited on space, one of my favorites is Gardenia jasminoides 'Radicans'.
The flower looks like this:
It is a very slow growing plant that only attains a height of 1 to 2 feet. It blooms a little later than most of the other cultivars and the flower size is smaller. The smell is still fantastic.
I hope this has given you some inspiration to go out and get yourself a Gardenia. I personally love my mine. I may be originally from the North, but along with the Magnolia, the Gardenia is a traditional symbol of the American Deep South.
Happy Growing!

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