Gardenia thunbergia from seed
Most gardenias grown along the Gulf Coast seem to be variants of G. jasminoides, an evergreen shrub; it is a plant everyone knows with a wonderfully fragrant flower. There are many cultivars for this plant that originates in China, Japan and nearby areas. The plant seems to be referred to by a confusing number of names: G. jasminoides veitchii, G. augusta, G. florida, G. grandiflora, G. radicans, and G. schlechteri.
The eastern part of South Africa is home to another species of Gardenia, G. thunbergia. G. thunbergia makes a taller plant and is sometimes called tree gardenia growing up to 3-5 meters. Though various information is provided from different sources, G. thunbergia is not usually reported as cold-hardy. But Silverhill Seeds offers seeds from plants rated as hardy into zone 7. Perhaps the plant is naturally hardier than suspected, or perhaps the seeds are from inland plants of the highveld and mountain forests.
I purchased some last year and they did not germinate; so I will try again. The plant seems like it has too much potential to give up. It too has a wonderfully fragrant flower, it is evergreen suggesting that it will not mind year round rain, and it is reputed to do very well in deep sandy soils amended with organic matter (Conroe).
Seeds of wild plants can be tricky to germinate. Some have requirements for exposure to heat, or rain, or chemicals in smoke. Others just need time, they need a winter or two for the embryo to mature or for germination inhibitors in the seed coat to dissipate. I have a few G. thunbergia seeds left and I'll order some more ($3.00). This time I'll put them out in gallon pots and treat some of them the same way I treat native hollies--just let them sit in sun and rain for 18-24 months.
For some of the remaining seeds, I will purchase a smoke disk and use it to pre-treat the seeds. A smoke disk is a bit of filter paper that is impregnated with chemicals from burning brush--the smoke is passed through the filter paper and the paper collects various bits of smoke. Later, the disk is mixed with a few spoonfuls of water, and the smoke chemicals leach out into the water--seeds to be treated are soaked overnight in the smoke-water.
Cross your fingers for me, maybe I'll get some seeds to germinate. There is no guarantee either of these methods might work, perhaps I'll have to try gibgerellic acid treatments, acid scarification, or some other approach. The fruit of G. thunberia is rock-hard and apparently stays on trees for years--maybe it needs to pass through a giraffe or elephant before germination is stimulated. Half the fun is in trying and learning.
Info: Smoke Disks, FineBushPeople.com
Here is a link that might be useful: G. thunbergia, PlantzAfrica.com