How to prevent and control the two rots in spring and summer?

Author: Zimo Mozi

In the blink of an eye, I have been learning to grow orchids for more than eight years. Perhaps influenced by my teacher, I have always liked to use the fine-material dry-growing method to cultivate orchids. Below I will discuss how this method prevents rot.

My growing medium is very simple. Its main components are 6 parts honeycomb coal cinder, 1 part humus soil (or ordinary garden soil, mountain soil), 1 part bark, 1 part tree-fern strips, and 1 part homemade organic fertilizer or other base fertilizer. From the formula, it is rather lean, and the fertility seems slightly insufficient, but it has achieved good results in preventing rot. Therefore I put great effort into creating the cultivation environment, striving to create a good growing environment for the orchids so they grow naturally, and their disease resistance also becomes stronger. When using coal cinder, I personally like to crush it; choose the smallest size of bark, and the tree-fern can be slightly larger. Mix them in proportion before use. Such a medium is fine and lean in fertility, and has strong capillary action in the pot. The medium in the orchid pot, from top to bottom and from inside to outside, has quite uniform dryness and moisture. The fine medium can also fully combine with the orchid roots, increasing the water-absorbing surface area of the roots. In this way, without watering frequently, I can very conveniently maintain the dryness and moisture of the medium, achieving the goal of moist but not wet, and dry-then-wet.

Because it is a fine medium, when planting orchids you can plant slightly deeper, letting the medium cover the pseudobulb, which helps produce more shoots (shoots can only sprout in darkness) and strong shoots. Moreover, after the seedlings produced each year mature, the pseudobulbs basically remain at the same level, and will not become deeper and smaller year after year because of uneven moisture in the pot. The gaps between seedlings are also relatively wide and clear.

With a fine medium, it is relatively easy to judge the timing when watering. Because the dryness and moisture of the surface medium directly reflect the condition of the medium in the pot, the watering timing will not be wrong. A fine medium is also quite suitable for dry growing; good capillary action will draw moisture from the bottom of the pot up to the surface medium, and the root base will not produce empty roots due to dryness. Each time it is dry, water; when watering, water thoroughly, dry-then-wet, with top and bottom well aerated. The orchid roots can absorb fresh air, and the medium in the pot is also unlikely to undergo secondary fermentation in warm weather.

In addition, rot prevention should begin in autumn. Based on personal observation and practice, seedlings with a high incidence of the two rots are mostly in direct proportion to excessive water and fertilizer and improper ventilation in autumn and winter. In autumn and winter, most people care most about vernalization and hardening seedlings, hoping to bloom well the next year and produce more and strong shoots. It is precisely this mindset that makes people unintentionally give more water and more fertilizer. Add to that an overly coarse medium, a big difference in moisture between the pot surface and inside the pot, and the watering timing is wrong. (Autumn has strong wind and dry weather. Most orchids grown in coarse material often have a pot surface that dries quickly while the inside of the pot is still wet.) Ventilation in winter must be given attention. Around noon, ventilation can only be done by opening windows a small area, then gradually increasing the ventilation. Never open windows wide and shut them wide; the harm this temperature difference brings to the seedlings ranges from scorched leaves to, in severe cases, stem rot during a warm winter, causing the death of the whole pot.

In autumn and winter, my understanding is that orchids enter the vernalization dormant period, their water demand is not great, so the water supply should be gradually reduced, keeping the medium mainly moist. Ventilation should be moderate, mainly by ventilating through a small opening; after each watering, according to weather conditions, ventilation can be appropriately increased. But never let cold wind blow directly onto the orchid seedlings, to prevent frost damage caused by temperature differences.

In March, strong seedlings can be moved out of the room first, and the water supply should also be appropriately controlled, not too wet; the pot surface is best kept dry. When the temperature is too low, move them back indoors or put down plastic film to prevent frost damage. In April, the temperature gradually stabilizes, and weak seedlings and old seedlings can also be moved out for cultivation. During this period, all orchid seedlings must not be fertilized too early, to prevent the medium from decaying in the pot and causing root rot and stem rot. Usually when watering, pay more attention to the difference between water temperature and air temperature; it is best to water when the water source temperature is close to the orchid pot temperature. I personally think that the method of using water temperature difference to promote growth is not advisable. Temperature difference is necessary, but not a sharp temperature difference; rather, it is the difference produced by the slow change of temperature over 24 hours a day, a kind of physiological stimulation given to the plant. A sharp temperature difference only harms the roots and stems and produces the two rots.

In May and June, orchid seedlings gradually emerge from the soil. At this time, the water supply can be slightly increased, fertilizer can be appropriately applied, and shade netting can begin to be drawn (according to the local environment, choose the appropriate shading timing). When the rainy season arrives, if there is heavy rainfall lasting more than two consecutive days, rain must be blocked, but before the rain-blocking work begins, be careful to let the medium in the pot be thoroughly soaked. During this period, run the humidifier less or not at all, and keep ventilation equipment running often to give the orchid seedlings fresh air often. Make reasonable use of sunny, ventilated weather to let the medium in the pot quickly become moist and then dry, thereby achieving the purpose of rot prevention.

In July, shading must be strengthened. The specific management has little to do with the two rots anymore, so I will not go into detail. Combining this with my own medium, I have briefly discussed cultivation management during the period when the two rots occur frequently. I hope everyone will give more opinions and more guidance.