Gardenia augusta

An Australian gardening fact sheet calls gardenias warm climate plants at their best in a mild, humid climate, above all in frost-free areas north of Sydney and Perth, and able to grow in Adelaide and Melbourne in a warm spot. It says they hate frost and cold climates.

The same sheet asks for slightly acidic, cool, moist, well-drained soil and some shade, above all from full summer heat in a hot or tropical climate, with full sun in cooler areas. It says to water well, particularly from spring to summer while the plant flowers, to mulch the roots and to feed in spring and summer. The NC State extension toolbox adds that the roots are shallow and resent disturbance and competition from tree roots, and that soil beside a concrete path or foundation may be too alkaline.

Little pruning is needed unless it is grown as a hedge, by the Australian sheet. The toolbox prunes in spring for shape, since flowers come on new growth, and the Missouri Botanical Garden prunes after flowering; both say not to feed in autumn, which brings on tender growth.

The Australian sheet lists the common problems: buds that fall or fail to open, yellow leaves in spring, root nematodes in sandy soil, and scale and mealybug, which it reads as signs of a plant under stress. The toolbox calls the plant moderately drought tolerant, and both American references rate its maintenance as high. The Australian Plant Census, which leaves out plants known only from cultivation, has no entry for it.

The Australian fact sheet names gardenias for mass plantings and hedges, as a background planting, as a standard in a pot, and in large pots, where it says they last for years in a good potting mix. It adds that the flowers can be picked for a buttonhole or posy but bruise easily. The Missouri Botanical Garden suggests siting plants near entries or paths so the fragrance can be enjoyed. Growers on HortOS list the species under its named forms: the fact sheet calls Florida the most commonly grown variety, gives Magnifica as a taller plant with larger flowers, and describes Radicans as a dwarf form of prostrate habit. HortFlora, the horticultural flora of the Royal Botanic Gardens Victoria, lists a run of newer cultivars as little known in appearance or history. No reference read gives a planting density.

Check the name: Gardenia augusta on a list is Gardenia jasminoides, the accepted name by GBIF, and the named form is what sets the size. The table above shows the sizes growers list, and the pot sizes guide explains the grades. For roots, pests and hardening off, the plant quality guide sets out what to check. Stock that crosses a state border moves under the state and territory biosecurity rules on moving plants and soil. The drawbacks the references give: it dislikes frost, the American references rate it high maintenance, and bud drop and yellow leaves are common.

The ASPCA lists gardenia, Gardenia jasminoides, as toxic to dogs, cats and horses. It gives genioposide and gardenoside as the toxic principles, and mild vomiting or diarrhoea and hives as the clinical signs.