Gardening: Gardenias and Florida
The gardenia with its beautiful, white scented flowers and dark green leaves are flowering and filling the air with their magnificent smell.
Gardenias are used primarily as free-standing specimens since they are easier to maintain when not surrounded by other plants. They are attacked by a number of pests and close proximity to other plant materials can increase the problems. Gardenias prefer full sun for best flower production but will tolerate partial shade. Heavy shade should be avoided.
Gardenias are represented in Florida primarily by two species: Gardenia jasminoides containing many varieties, and gardenia thunbergia, grown primarily as a rootstock. Gardenia jasminoides is native to China and gardenia thunbergia is native to South Africa. Gardenia thunbergia is valuable due to its resistance to nematode attack and vigor for species grafted on its roots. In Florida gardenia varieties are available grown on their own roots or grafted on rootstock of gardenia thunbergia. Grafted plants are more vigorous and produce more and larger flowers.
Gardenias grow in a variety of soil conditions but do best in a well-drained soil high in organic matter. Soil pH is important since it affects availability of mineral elements and should be maintained near 6.0. If the soil does not naturally contain a high level of organic matter you should add peat moss, manure or other organic materials to your planting site. Thoroughly incorporate the soil amendments to a depth of 6 to 8 inches. This will increase the water holding and nutrient retaining capabilities of sandy soils.
Proper fertilization is important to growth and flower production. Four times a year is recommended - winter, spring, summer and fall. Acid fertilizers with an analysis of 6-0-6 or 8-0-8 are recommended. Use a fertilizer with minor elements twice a year but not more than that as the minor elements can become toxic to gardenias at relatively low concentrations on some soils. The most frequent cause of chlorosis in gardenias is due to a lack of iron, usually resulting from a high soil pH, which you can try to correct by lowering the soil pH using sulfur.
Pruning should be done just after the plant has completed its flush of bloom, usually in June. Pruning after October 1st will decrease the number of blooms the following year. Buds are initiated and developed by a combination of short days and long nights, low temperatures and wood of the proper age.
Watering is also important for flower production since it controls the number of flower buds that will remain on the plant to maturity. If water stress occurs in a heavily budded plant a large number of buds will fall before they open. Therefore, soil should be kept moist while the plant is in bud and large variations in soil moisture should be avoided.
Premature, flower bud drop of gardenias often plagues home gardeners and is frequently caused by root injury and other factors including nutrition, insect injury and climate conditions.
Root injury may occur as a result of nematode infestation, poor watering practices, poorly drained soils, excessive fertilization and mechanical injury. Nematodes in the soil will damage roots and prevent normal uptake of water and nutrients. Poorly drained, wet soils, or excessive watering will cause root injury due to oxygen deprivation. Application of excessive fertilizer can cause dehydration of root systems due to excessive soluble salts. Mechanical injury to roots occurs most often during transplanting. Use care to prevent as much damage as possible.
Insects can damage unopened flower buds and cause them to drop. Thrips and aphids are most troublesome. Aphids can be seen but thrips are small and can go undetected until considerable damage has occurred.
When weather is excessively hot and dry the possibility of bud-drop is prevalent since the plant is unable to absorb water rapidly enough to compensate for water loss through transpiration. Maintenance of adequate soil moisture will aid in reducing water loss and bud drop under these conditions.
Many varieties of gardenia can be grown in Florida. There is considerable variation in flower size and form, blooming time and duration, and plant growth among varieties. The following is a list of some varieties available in Florida.
- Ameii Yoshioka: Flowers of this variety are outstanding, measuring 4 to 5 inches in diameter and have the desirable camellia flower form. Foliage is a brilliant dark green. It is a vigorous grower and produces an abundance of flowers in late spring.
- August Beauty: Distinctive due to its dark green, long pointed leaves and late blooming period. Flowering occurs sporadically during summer but heaviest bloom occurs in late August.
- Belmont: This is a vigorous grower with dark green foliage and large flowers, 4 to 5 inches in diameter, produced throughout much of the growing season.
- Coral Gables: Produces large flowers on compact plants. Dark green foliage with large fragrant flowers which bloom throughout summer months.
- Glazeri: Flower production is heavy on this variety and foliage is medium green color. Peak bloom occurs in April in South Florida.
- Hadley: Flowers are produced in early spring above black green foliage. A vigorous grower with large flowers.
- Miami Supreme: Produces large flowers 4 to 6 inches in diameter above dark green foliage.
- Mystery: A compact, bushy plant with glossy, dark green foliage. Large fragrant flowers are produced during the summer months.
- Radicans: A miniature sized gardenia with compact, spreading growth habit. Small flowers are produced profusely in early summer. This variety makes a good ground cover.
Eileen and Peter Ward have owned a landscape and lawn maintenance company for 35 years. Eileen can be reached at Gswdmarco@comcast.net or 239-394-1413.