Analysis of the water retention rate in the pot in orchid cultivation

Orchids grow best when the water retention rate of the potting medium is 90%-60%, and the humidity inside the pot is at an ideal state. Pot up with dry potting medium, weigh the orchid together with the pot at 1000 grams, water thoroughly with a large amount of water, let it sit for a while, and wait until no gravitational water flows out from the bottom of the pot, then weigh again: 1400 grams. That is to say, at a water retention rate of 100% (fully saturated with water), the weight of water absorbed is 400 grams, and the ideal weight of water in the orchid pot is 360 grams-240 grams, meaning the ideal total weight of the whole potted orchid is between 1360 grams and 1240 grams. Above 1360 grams is a wet state, and below 1240 grams is a dry state. Therefore, after watering the orchid, ventilate it as soon as possible to bring the pot weight within 1360 grams as quickly as possible, then place moist sphagnum moss on the surface of the pot to retain moisture, so as to prolong the time it takes for water loss to reach 1240 grams. When the weight of the pot falls below 1240 grams, it can be watered. This is a method I learned online. I used this method to manage one pot, and for all the others with the same potting medium I followed the same timing. So far the results have been quite good.

1. The saturated water content at the maximum water retention rate of 100% of the substrate is not used as an experimental specimen because the thick water film formed by a long period of high water content prevents the roots from contacting oxygen, causing the roots to undergo anaerobic respiration and eventually rot, which seriously affects growth. Therefore, there is no need for an experiment.

2. At 90% of the maximum water retention rate of the substrate, because the surface water film on the roots and in the substrate is relatively thick, the roots can absorb part of the water and can still maintain an aerated environment in the substrate, so the leaves grow rapidly, but respiration is insufficient, so nutrient accumulation is not high.

3. At 70% of the maximum water retention rate of the substrate, the roots have a good respiratory environment, grow rapidly, accumulate abundant nutrients, and the plants grow plump.

4. At 50% of the maximum water retention rate of the substrate, the roots have difficulty absorbing water, growth is greatly inhibited, and seedlings die after 60 days.

5. At 30% of the maximum water retention rate of the substrate, there is only slightly more water in the substrate than bound water, making it very arid. The roots have extreme difficulty absorbing water, and there is even no water available for absorption. Because the seedlings rely on the mature plant's pseudobulbs for water, once the mature plant's water is excessively depleted, the seedlings are the first to die, and in the end, after the water in the mature plant's body is completely depleted, it also dies.

From this it can be judged that 90%-60% of the maximum water retention rate of the substrate is the stage in which Chinese orchids go from gradually suitable to most suitable to gradually suitable for growth, while exceeding 90% of the maximum water retention rate and falling below 60% are both unfavorable to the growth of Chinese orchids.