Dregeas come from Asia and are evergreen in the wild, but if you keep them in your greenhouse with low winter temperatures, they will lose most of their leaves. They are also known under their synonym Wattakaka sinensis.
It is a climbing plant that will flower every spring with white flowers that have a splash of pink in the centre. They are highly scented, which usually means in these type of plants that they are moth-pollinated. The flowers last for up to a week and resemble hoya flowers. Not surprising as Hoyas and Dregeas are related. Another asclepiad species that has highly scented moth-pollinated flowers is Araujia sericifera, although the flowers on that plants do not resemble Dregea flowers.

Dregea sinensis

Dregea sinensis

As with Hoyas, Dregeas rarely set seed in the greenhouse, but when they do, they form twin-seed horns which will burst open when ripe and can contain up to 50 seeds. The seeds remain viable for up to a year, but it is better to sow them as soon as possible. If you sow them straight away, you will get almost 100% success; if you leave it till 3-6 months, you will get 25-50%; and after a year, you may only get one or two to germinate.
The leaves are heart-shaped and fairly large. It is possible to propagate this plant by cuttings, preferably in the spring. I use cuttings with two nodes, one for the roots and one for the new growth, just as you would do with Hoyas. They can be grown in shade or full sun and will grow outside in the summer. They can have a bit of frost (-2 or 3°C), but it is better to give them some protection.

This caudiciform species comes from China and is very easy to grow. It can be grown outside in the garden in the summer, or just as easily in a pot. It can take a little bit of frost, especially if the soil is very sandy and well-drained. If you do not have this sort of soil, it is advisable to take them out before the winter and treat them as you would Dahlia tubers. The tubers are potted up in spring and can be either buried completely or half above ground so you can still see the tuber (see photo below). The plant prefers cool conditions (10-18°C); if the temperatures are too high (for instance, if you keep them in a greenhouse where the day temperatures get above 25°C), the flowers can become misformed.
The flowering period is from May to August and the colour of the flowers can be pink or white; the variety show in the picture is ‘Snowtop’. This genus does also have a yellow-flowered species, Incarvillea lutea, but that is a very rare sort.
Seed collected one year can be sown the following spring. The plant will form a tuber that first year and will flower the following year, so two years after collecting the seed. It is a relatively pest-free plant, but watch out for greenfly.

Incarvillea delavayii Snowtop tuber

Incarvillea delavayii Snowtop flower

Just added to the website: photos of Impatiens mandrakae and sp. China yellow.

The mandrakae is a small creeping species from Madagascar, quite easy to grow, with tiny translucent green flowers. Definitely not hardy.

I do not know the botanical name for sp. China. If anyone can help ….? It looks a bit like I. stenantha, but it is less speckled than stenantha. I do not know if it is hardy; I keep it at 10 degrees C.

Impatiens sp. China

Impatiens mandrakae