There are around 30 species belonging to this genus, native mostly to subtropical regions. A few of them are capable of enduring polish climatic conditions, but only Celastrus orbiculatus - Oriental bittersweet is universally used.
| Celastrus orbiculatus (photo Sz. Marczynski) |
In some collections you can also encounter Celastrus scandens - American bittersweet, a similar species from the same genus. Both species have vigorous twining stems and are dioecious. They bear inconspicuous, white to greenish flowers, gathered in clusters. Fruits appear only on female plants pollinated by neighbouring male specimens. Rounded yellow three-valved capsules split open at maturity to reveal closely packed seeds completely enclosed in fleshy red or orange arils. Upon ripening the yellow outer covering contrasts beautifully with the red or pink inside. The fruits stay decorative for several months and make an excellent addition to dried flower arrangements or interior decoration.
Celastrus orbiculats - Oriental Bittersweet is native to Japan, China, and Korea. It grows very vigorously attaining the height of 12 m (1-4 m of new growth a year). The stems are covered with numerous small axillary buds with spine-like outer scales. Rounded or elliptic, finely toothed leaves turn bright yellow in autumn. The flowers are usually gathered in leaf axils.
 Celastrus orbiculatus (photo Sz. Marczynski) |
Two varieties are encountered in cultivation:
- 'Diana'- a profusely fruiting female clone (it sets fruit only if there's a male clone in the neighbourhood that can pollinate its flowers).
- 'Hercules' - a male clone, a good pollinator for female plants, also for 'Diana'. It ensures abundant fruit crop. It can grow separately from a female plant and is widely used in places where berries are not welcome, for instance in children’s gardens or along the roads outside the city boundary.
Celastrus scandens - American Bittersweet is native to northern America. It's less rampant than Oriental Bittersweet - it attains the height of about 7 m. It's not popular in Poland, as it rarely sets fruit in our cool climate. Flowers appear in terminal panicles, which distinguishes it from C. orbiculatus.
Requirements.
It can grow in all types of soil, including drying soil. It's better to plant it in poor soil, as in the fertile one it can become too expansive. Well adaptable to different levels of pH of the soil. Tolerates half shade, but thrives and yields best fruit in full sun. It's frost hardy and only rarely affected by pests and diseases. Responds well to pruning.
 Celastrus orbiculatus over the entrance to the block of flats in Warsaw's district Ursynów (photo Sz. Marczynski) |
Application.
Ideal for public open spaces. It is well suited for covering tall fences, solid structures (arbours, pergolas, arches, unsightly buildings etc.), and makes a good plant for creating noise barriers along roads and motorways. It looks interesting when climbing up old tree trunks or large trees. Due to its rampant growth, however, it shouldn't grow next to bushes, small trees or conifers as it may choke them up. It may also grow in large containers on balconies or terraces, if you want to create a green screen. If grown in a suitable place and kept in check by pruning, it will adorn any garden without posing any threat to other plants.
You should only buy vegetatively propagated plants from a reliable source, as only such plants will grow best and yield fruit. Avoid purchasing seed-propagated plants of unknown sex, so frequently encountered in commerce.
 Celastrus orbiculatus in the gardens of the Library of Warsaw University , Poland (photo Sz. Marczynski) |
 Celastrus orbiculatus 'Hercules'(photo Sz. Marczynski) |
 Celastrus orbiculatus in the gardens of the Library of Warsaw University, Poland (photo Sz. Marczynski) |
 Celastrus orbiculatus in the gardens of the Library of Warsaw University, Poland (photo Sz. Marczynski) |