Leaf Color

Question

I have been an amateur grower of orchids for a long time, cultivating my plants in a greenhouse environment on my small farm located in the interior of my state in Brazil. This place is located 1,970 feet above sea level. In the summer it reaches 100º F and in the winter it averages 55º F, with some days as low as 40º F. I do not cool or heat my plants. Unfortunately, for some years I have noticed that many of my plants (about 2,000) have a deficiency or eventually some illness. The leaves become yellow at their apex (upper part of leaves) and I am not able to detect the cause, even in a laboratory examination. This yellow coloration then extends down the pseudobulb. I have't noticed any damage on the new shoots. The plants that show more problems in flowering are the Laelia purpurata-types. My plants are grown in tree fern. - Helio Luco
 

Answer

I believe your plant's problem is nutritional, rather than a disease. The yellowing leaves are all on the oldest pseudobulbs, which shows that the plant is taking nutrients from them and using these nutrients to maintain growth. Very likely it is a deficiency of nitrogen, but it is also possible that a lack of iron and other elements is the cause of the problem.

Try a slow-release fertilizer called Nutricote. It is formulated in Japan for a similar temperature range to what you experience. The eight- to nine-month formulation, when applied in spring will basically carry you through until the following spring. If this is not possible to obtain, any good slow-release product or a balanced liquid fertilizing program will start your plants into rapid growth. Also, the minor elements need to be supplied, especially calcium, as you are growing in treefern fiber. If you do not have a liquid fertilizer with calcium in it then you should consider adding six pounds dolomite lime to each cubic yard (3 Kg/cm meter) of treefern fiber and mix in well. -Andy Easton