Gardenias

Gardenia
Family Rubiaceae
There are around 200 species, and many named cultivars.
They are good as a scented feature plant amongst other shrubs, as a tub plant; or more specifically as a hedge, or in a mixed with tropical foliage plants to create a tropical effect.
These evergreen shrubs or small trees, have rich green leaves, and white or yellow flowers; usually large and often fragrant.

A protected position in warm climates is preferred; though they do grow in mild to cooler temperate areas (eg can do well in Melbourne). Provide protection from hot, dry winds. Protect from heavy frosts. Grows well under a canopy of large trees, provided shade is not excessive. Filtered sun is ideal but in hot tropics, gardenias will tolerate full sun well. Full shade may impede flower production and bushy growth.

Soil should be fertile, moist and well drained.

They respond best to a high organic soil, so annual applications of well rotted manure or rich compost are valuable.

Annual fertilising is very beneficial. Pruning is only necessary to maintain a good shape, or revitalise old plants (flowers are best on healthy new growth).

Don't plant large or dense shrubs close by, as they reduce air flow and this can encourage development of disease.

They grow well alongside ground covers or low plants, that keep the roots, and foliage cooler (eg. Iris, Lonicera, Lobelia, Verbena and Vinca are good companions, liking similar light and soil conditions).

Propagate by semi-hardwood cuttings.

Pests may include aphis, scale, mealy bug, thrip and even mites.

Diseases can include leaf spots, canker, powdery mildew or botrytis attacking the young buds. Sooty mould may grow as a result of insect infection.

Magnesium and nitrogen deficiencies often cause yellowing of leaves (if soil is excessively wet, it may be nitrogen; but if soil is well drained, magnesium deficiency is more likely the problem).

Cultivars

Most cultivated varieties are thought to have been bred originally from G. jasminoides (syn. G. augusta)

G. Florida -to 2m tall, flowers to 8cm diameter. Produces more flowers per bush than most G. jasminoides varieties. Thought to be a variety of C. jasminoides.

G. grandiflora ‘Star’ – a dwarf version of the large growing G. grandiflora. Small highly scented white star-like flowers.

G. jasminoides (Gardenia) -a glossy foliaged shrub, to 1.8m tall, with scented white flowers. Flowers are generally larger than those of G. Florida. There are several named varieties of jasminoides commonly grown, eg. ‘Magnifica’, ‘Professor Pucci’, ‘Aimee Yoshiba’, ‘Golden Magic’.

G. Radicans -to 60cm tall, spreading to 2m diameter; thought to be a variety of C. jasminoides.

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