Plant Doctor Archive

Callas and Clivias

I HAVE two problems, the first with arum lilies planted near the fish pond. They get brown splotches on the leaves while the same varieties in other parts of the garden are not affected. Also, can you tell me what causes tip browning on clivias as the leaf gets older?

THE leaf sample you sent looks more like a calla (Zantedeschia) than a true arum, but name changes take a long time to become widely used and lots of gardeners still refer to them all as arums.

In damp soil, callas are rather susceptible to a bacterial disease called Erwinia that causes rot in the tubers as well as brown patches on the foliage and sometimes the flowers. The soil near your fish pond may not drain as well as the rest of the garden, hence the problem being confined to that area. Unfortunately, it is a difficult disease to get rid of, so probably the best thing to do is dig up and destroy the affected tubers and only grow callas in well-drained parts of the garden.

Dieback of clivia leaves is an interesting question. With most other plants, leaf tip dieback is usually the result of salt accumulations through over fertilising, or drought or poor drainage or some other problem affecting the root system. But with clivias, no immediate answer springs to mind, so I checked with clivia breeder Dr Keith Hammett who says that although some experimental work has been done to try to determine the cause of clivia leaf dieback there have been no clear results as yet. Keith has seen leaf dieback on clivias in the wild and says severely affected plants may collapse almost completely, but they usually recover some time later. To keep clivias looking their best he suggests you remove the affected leaves or trim off the brown portions carefully with sharp scissors. But rather than slicing straight across the leaf, cut them into the same shape as nearby leaves to maintain a natural look.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.