What are the four major factors that cause stem rot in orchids?

    In the process of growing orchids, nothing hits growers harder than stem rot, especially during the high-temperature weather of the four months of June, July, August and September. By the time you notice blackening, yellowing or wrinkles on the leaves of the orchid plant, it is all too late; even if Hua Tuo were alive, there would be no power to turn the tide, and the whole lot will still be wiped out and gone forever. If a promising wild-collected seedling dies, all that is left to the grower is long, endless sorrow accompanied by loneliness.

    Having grown orchids for more than 10 years, I recently ran into this same miserable business once again. On July 10 this year I had just bought a clump of round-headed wild-collected Cymbidium tortisepalum from Qimulin, Shidian, and it was the most promising of all the wild-collected orchids I grow. By noon on September 21, when I was planting it, I found a black spot at the tip of one leaf, and when I opened it up to look, it was too late: it was the terminal disease stem rot, with the neck all the way to the pseudobulb completely blackened. In that instant it was like a thunderbolt from a clear sky, and I was truly furious and grief-stricken; that mood lasted about a week, and the shadow of it often ached in my heart in the days that followed, forcing me to think and sum up as calm as still water the four major causes of orchid stem rot, so as to discuss orchid growing techniques together with the broad community of orchid growers and jointly promote Chinese orchid culture. The four major causes of stem rot are as follows:

  1. Temperatures too high

During the high-temperature weather of the four months of June, July, August and September, daytime temperatures often stay at 25-31°C, far exceeding the safe temperature for humidity management in orchid growing, providing the temperature conditions for the rapid breeding of disease bacteria; the fastest can cause a directly infected plant to rot in about 30 minutes, and the rest can all be infected within two days. By the time you discover it, there is no saving it.

  2. Fertilizer burn from the potting medium

When using leaf mold, bark, tree-fern root and other humus materials to grow established plants and wild-collected plants, they must be fully fermented before use; avoid using sheep manure, chemical fertilizers and other potting media with excessive fertility, especially when growing wild-collected plants. If the previous two points are neglected, under high-temperature conditions total wipeout is most likely, so let all friends remember: the nutrients from the humus material alone are enough to sustain two years of nutritional needs.

  3. High humidity

The main factor causing stem rot is water. In high-temperature weather, excessive moisture in the potting medium, excessive environmental humidity, alternating too dry and too wet conditions, and choosing the wrong time of day to water so that water accumulates in the core leaves and pseudobulbs can all easily cause water rot of orchid leaves and orchid root tissue, resulting in stem rot and collapse of the plants.

  4. Poor ventilation

Strengthening ventilation is an effective measure against excessively high temperatures and excessive moisture. After watering, it can quickly lower the temperature and evaporate away the surplus water; in high-temperature weather, generally 2-3 days of ventilation will solve the problem. Where natural ventilation is poor, fans can be set up as a remedy.

Stem rot generally occurs under humid, muggy, high-temperature weather conditions. When watering, choose a low-temperature time of day, and after watering promptly take measures to lower the temperature and strengthen ventilation until the potting medium is safe. By paying attention to solving the above problems, you can effectively avoid the occurrence of stem rot, and growing orchids will then be effortless.

                Author: Jin Ye