Rusk Citrange,Trifoliate Orange and Willets Citrange.
This is a row of two year old seedlings of Morton citrange, growing outside but with some protection from the side of my winter heated greenhouse.
It can still get very cold here, as the picture taken in January 2001, confirms!
About 100 years ago, the first controlled crosses were made between the hardy Japanese Bitter Orange, Poncirus Trifoliata, and the Sweet Orange, Citrus Sinensis. These are sometimes known as Citroncirus, but more popularly as Citrange. There are now many named varieties, often grown as root-stocks for commercial citrus varieties. The promise of delicious, cold-hardy citrus has not been realised, but these plants survive considerable frost and should be more widely known. I have yet to discover a fruiting Citrange growing in Britain. Does anyone out there know of one??
Unfortunately, I haven't managed produce any fruiting citrange plants, so I can't show you any photos of the fruit. However, I have scanned some prints taken from 'Yearbook of the Department of Agriculture, 1904.' This book contains an article about "New Citrus Creations" by H. Webber and W. Swingle, describing the very first Citranges.
Hardy to about -10C
These hybrids were first produced around 1909 by crossing the Willets and Rusk citranges with the round or oval kumquat. The best known varieties are called Sinton, Telfair and Thomasville. I am growing this last variety, named after the town of Thomasville in Georgia, USA where it grows happily outside the normal range of citrus.
The most unusual feature of this fruit is the five-pointed calyx, which is much longer than in any other citrus variety. Strange how the hybridisation has created a novel feature not present in the parents!
Hardy to about -8C
Hardy to about -8C
This hybrid of three species, named 'Glen' has leaves of many shapes. All the leaves in this picture were taken from a single plant. The fruit is small, orange and sour.
page updated 8th October 2004
This page covers the hybrid Citranges and further complex hybrids of them. The Poncirus parentage invariably results in some degree of cold hardiness but also some bitterness in the fruit.
Leaves of Poncirus trifoliata (top), citrange and sweet orange. The citrange leaf is very clearly a half-way-house between the other two.
This complex hybrid, sometimes still called a citrange, and sometimes used a rootstock, is said to be closest yet to the goal of a hardy sweet orange. I believe it is probably also the variety sold as 'Snowsweet.'
I obtained budwood in 2001, and budded on to Poncirus trifoliata. The plant grew well and I planted it outside in spring 2004, somewhat protected by a fence and concrete posts. However, it seems to be lacking nutrients and, as you can see in the second photo the leaves have turned very yellow.
Hardy to about -12C?
ripe fruit and cross-section
of ripe fruit
not yet mature
Poncirus trifoliata x Citrus sinensis
Citrange x Kumquat
Citrange x Calamondin
(C. paradisi " Duncan" x Poncirus trifoliata) x C. sinensis "Succory"
Morton citrange growing outside in October 2004. The new 1m (3ft) tall shoot may well be damaged by any hard frosts this coming winter