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Senna corymbosa - Growing Guide
Caring for Senna corymbosa
(Formerly Cassia corymbosa)
Although frost tender this evergreen plant is one of our most popular greenhouse or conservatory plants and it is odd not to find the odd flower on a mature plant right through the year.
Although Senna corymbosa originates from northern Argentina and Uruguay it can be grown outside in the mildest locations on a warm sunny wall where the wood will ripen and many more flowers will result. The largest plant which we have managed to grow outside at Burncoose reached 6-8ft in height with a similar spread.
It is advisable to prune back the old stems by 12-18in in spring again to encourage vigorous new growth from which more flowers will appear. The same is true if this plant is grown in an open bed or in a large pot in the greenhouse. A light annual pruning will reinvigorate the plant.
S. corymbosa has glabrous leaves with two or three pairs of leaflets. The normal and main flowering season is in late summer but, under glass, flowering can be more irregular especially if a secondary pruning has taken place in summer to try to keep this quick growing plant under control. Again it is the resulting fresh new growth which produces the flowers. With all the cuttings taken from our stock plant in the Burncoose conservatory the pruning process was ongoing.
The flowers are rich yellow and appear at the ends of the axillary shoots in clusters of three to eight. Individual flowers are up to ¾in across and the clusters can be 4in across.
Propagation by softwood or harder semi ripe wood is fairly straightforward with bottom heat right through the growing season. If your greenhouse is heated and frost free the plant will not go dormant as it would if grown outside. A crop of cuttings is then available at more or less any time of the year.
Only very occasionally have we had problems with some white fly infestation at Burncoose. If red spider mite attacks give the plant a good prune back and remove all the pruned foliage and branches. It will quickly reshoot.