Key Points and Precautions for Foliar Fertilization of Orchids, with a Discussion on the Prevention and Control of Edible Fungus Pests and Diseases

In the cultivation of Chinese orchids, orchids mainly absorb nutrients through their own root systems, and root-external fertilization is rarely needed. Therefore, root-external nutrition is not as important as root nutrition, but under special circumstances, root-external nutrition still has certain significance. For example, when orchids show nutrient deficiencies, fertilizer should be applied promptly to compensate. In practical operation, foliar fertilization can relatively easily eliminate the symptoms of nutrient deficiency in orchids. In addition, foliar fertilization is also a better way to supplement fertilizer for orchid plants with rotted roots.

I. Advantages of Foliar Fertilization of Orchids

1. Directly supplies nutrients and avoids potting soil compaction. Certain nutrient elements such as iron (Fe), manganese (Mn), zinc (Zn), etc., are easily fixed after being applied to the potting soil, and their effectiveness is greatly reduced. If changed to foliar fertilization, it can avoid potting soil compaction and also improve fertilizer efficiency.

2. Nutrients move quickly, and results can be seen in a short time. Spraying fertilizer on the leaves takes effect faster than root fertilization, and it can ensure the timely supply of nutrients. Practice has proved that foliar spraying of urea can take effect in 1 to 2 days, while applying it to the potting soil requires 5 to 6 days. Another example is phosphate fertilizer: one foliar spray can take effect, but root fertilization requires 10 days to take effect.

3. Saves fertilizer and does not damage roots. The amount of fertilizer used for foliar spraying is usually only about 20% of the amount used for potting soil fertilization. Taking the spraying of "Huabao" as an example, 1 gram of Huabao is dissolved in 1 liter of water (that is, diluted 1000 times with clean water), and sprayed on both the front and back of orchid leaves. The amount used is small, and only 1/5 of the amount used for watering the potting substrate is enough. Foliar spraying of trace element fertilizers not only saves the amount used, but also avoids damage to orchid roots caused by uneven application to the potting soil.

4. Makes up for the insufficiency of stopping root fertilizer application. During the severe heat of midsummer and the severe cold of deep winter each year, root fertilization must be stopped, but this does not mean that orchid plants do not need nutrients. At this time, the safest way to supplement nutrients is foliar fertilization. Foliar fertilization can be carried out throughout the year. In summer, choose slightly cooler weather, and in winter, choose a mild time for foliar fertilization, which can achieve relatively good results, thereby making up for the insufficiency of stopping root fertilizer application.

5. Saves time and reduces the number of sprays. Foliar fertilization can be carried out together with procedures such as pest control and sterilization. In the foliar fertilizer solution, add an appropriate amount of omethoate (to kill scale insects, etc.) and 75% chlorothalonil (for sterilization). This not only applies fertilizer, but also kills pests and sterilizes. In this way, it saves time and reduces the number of sprays, achieving twice the result with half the effort.

II. Issues to Note in Foliar Fertilization of Orchids

1. Non-water-soluble fertilizers cannot be used. For different fertilizers of the same nutrient element, the speed of foliar absorption is different. For the same potassium fertilizer, the fastest absorbed by leaves is potassium chloride, followed by potassium nitrate, and then potassium dihydrogen phosphate; for the same nitrogen fertilizer, the fastest absorbed by leaves is urea, followed by nitrate nitrogen fertilizer, and then ammonium nitrogen fertilizer. Fertilizers used for foliar spraying can only be water-soluble; non-water-soluble fertilizers cannot be used.

2. Pay attention to solution concentration and reaction. The principle is to appropriately increase the solution concentration on the premise that the leaves are not harmed by fertilizer. This can improve penetration efficiency and produce better results, but be sure to pay attention to appropriateness.

3. The time of wetting orchid leaves. Generally, the fertilizer solution is required to keep orchid leaves wet for 30 minutes to 1 hour, so that absorption is fast and the effect is good. If it dries quickly, the effect will be poor. If it is exposed to rain shortly after spraying, the effect is also poor. Therefore, foliar spraying should be carried out on a clear evening or in the early morning with dew, and windless weather is better.

4. The spraying site should be reasonable. Stomata are the entrances and exits for gas and water during plant photosynthesis and respiration, so the foliar spraying site should be reasonable. For example, about 85% of the stomata on Cymbidium goeringii leaves are on the back, and only 15% are on the front, so when fertilizing, special attention should be paid to spraying the back of the leaves. Other varieties of Chinese orchids are roughly the same, and emphasis should be placed on spraying the back of the leaves.

5. The water quality must be clean. The water used to dilute fertilizer must be clean; turbid water containing impurities cannot be used. If tap water is used, it must be stored for more than one day and used after the chlorine has dissipated.

6. A single fertilizer cannot be applied for a long time. Different fertilizers should be sprayed at different growth stages of orchids, and a single fertilizer cannot be applied for a long time. For example, in spring when new orchid shoots emerge, nitrogen fertilizer should be the main type, such as urea, Huabao (No. 5), etc.; from the beginning of July to the end of August, in order to promote flower bud formation, phosphorus fertilizer should be the main type, such as Huabao (No. 3), potassium dihydrogen phosphate, etc.