Forsythia x intermedia Karl Sax

Forsythis x intermedia “Karl Sax” – Golden Bell

Bright yellow flowers, about 4cm across, cover the bush and arrive before the leaves.


This is a bushy shrub growing 2M tall, flowering on one or two year old growth. Karl Sax has a slightly more spreading habit than other forsythias and blooms about a fortnight later. However, it is still one of the earliest flowering shrubs, as opposed to small trees, in Karin’s Garden. The flowers of Karl Sax have a distinctive orange throat.


Forsythia comes from China though they have long been cultivated in Europe and America. It is named after the Scottish botanist William Forsyth (1737–1804) who was a founding member of the Royal Horticultural Society.

F. x intermedia was raised in Göttingen Botanic Gardens in 1878, and is a hybrid of F. viridissima and F. suspensa var. Sieboldii. F. x intermedia was added to the collection at the Arnold Arboretum in the USA in 1889. They treated the diploid F. x intermedia “Spectabilis” with colchicine to produce a tetraploid version called “Armold Giant”, which they back crossed with F. x int “Spectabilis” to produce many seedlings, including two famous varieties; Beatrix Farrand, and “Karl Sax” which was introduced to the world in 1960. The original clone of Beatrix Farrand has now been lost and it appears that not all plants sold under this name are actually the same. Unusually for a Forsythia, “Karl Sax” is self-fertile.

Soil / Aspect:

F. x intermedia “Karl Sax” is a robust plant that tolerates a range of soils, provided only that it is reasonably well drained. It flowers best in full sun and is reasonably drought tolerant. In Karin’s Garden this flowers in mid-march when the lack of frosts allows the flowers to last longer than in places such as, say, continental Europe.


Whilst F. x intermedia can be pruned as a hedge, this should be avoided as keeping the hedge tidy inevitably removes most of the flower buds. Flowering is best on younger “old” wood, so stems more than three years old should be removed as near the base as possible. This normally involves taking out about one third of the main stems each year.