This just started, the yellow leaf in the picture took only a few days to go completely this colour! I've taken the plant out of the pot and it looks good, slightly moist and no evidence of pests or disease. Can you diagnose the cause of this, please? I've attached pictures of good leaves and the problem ones and, by the way, new leaves are coming on! Thank you, Murray
Murray, is that plant in full sun? You might want to move this thread to the Aroid section, where you will get some expert advice
The specimen in your photo appears to be a hybrid known as Alocasia Amazonica. Depending on the source, the hybrid was created by crossing Alocasia watsoniana x Alocasia sanderiana while another source indicates the parentage to be Alocasia watsoniana x Alocasia noblis. Alocasia Amazonica is often confused with Alocasia micholitziana (mik-oh-lit-zee-AY-nuh) which is often sold commercially with the trade name Alocasia 'Frydek'. Even though some websites claim Alocasia Amazonica is difficult to grow, in fact it is quite easy. The trick is you must provide the plant the conditions it requires. This plant specimen will not do well as a "house plant" on the interior of the home unless it is receiving at least moderately bright light. You also cannot forget to water the plant on a regular basis. This is a hybrid of rain forest specimens and requires damp (not muddy) conditions to prosper. However, like many Alocasia sp., if planted out doors Alocasia Amazonica will often go dormant when the temperatures drop much below 12.75C (55 degrees F) and you may not see it for some months until spring and warmer weather returns. In most cases the specimen will grow again once the temperatures rise and stabilize again. But this specimen will not tolerate a freeze! Recent reports from knowledgeable growers indicates the true parent species are often found growing in very bright light, almost direct sunlight. If grown in too low light the Alocasia often looses much of its green color on the upper surface of the leaf and becomes almost black. In low room light, especially without water, the specimen is likely to simply droop, loose the color, and die a slow death. However, it will grow well in medium filtered light. As a house plant, keep it near a bright window. If you wish to grow Alocasia Amazonica in direct, or near direct sunlight, this plant can require a great deal of water. However full sun may not be advisable in some areas where the summer sun is extremely hot and brilliant. The specimen can stand as tall as 4 feet but typically is only 2 to 3 feet in height. Native growers of the parent species indicate they reach a more impressive height in brighter light. The natural growing media for this plant is a well aerated soil. You can duplicate this mix with a soil mix growers often call a "jungle mix". You can easily make it yourself with a good "moisture control" potting soil mixed with bark, such as orchid potting media containing charcoal, coarse Perlite™ and peat moss. Keep the soil evenly damp. There are differences of opinion however. Expert aroid hybridizer and grower LariAnn Garner offered these observations, "In my experience, this plant can suddenly rot away to nothing if kept too moist for too long. Some of the healthiest specimens I've seen are allowed to dry out almost to the point where you'd be alarmed. I believe this is important to prevent the buildup of pathogenic microbes; the periodic drying apparently keeps them at bay. The "jungle mix" is a great idea; I would use even less of the moisture control potting mix, especially if you are going to use peat moss in the mix, and I'd up the bark, coarse Perlite and charcoal. I find this to be true with all the other longiloba types as well. I suspect it is because in their native habitat, the roots grow in the loose upper layer of the forest floor, consisting of leaf litter, small twigs and other very open debris. Most of our soil less media mixes stay too wet to simulate this kind of environment." And by the way, it is quite natural for a leaf to die from time to time.
