When people ask us why their Paphs do not grow well for them, the problem is usually how they water. Proper watering is key to growing quality Paphiopedilum.
Good quality water goes a long way towards improved Paph culture. What is good quality water? It is water that has a low total dissolved solids (TDS). In nature, most of these plants are not exposed to salts and high mineral content in the water. It falls from the sky with a TDS of zero and only a small amount of mineral content is picked up from the substrate and decomposing organic matter around the roots. Rainwater or reverse osmosis (RO) water are best for your plants. Tap water or well water that has less than 75 ppm TDS is also ideal.
You can grow your Paphs well in harder water, but it takes some extra efforts. Our well water is the nursery can be 250 ppm TDS or more. We manage this with frequent deep leaching and frequent repotting. Since we fertilize very heavily (inorganic fertilizers increase the TDS of the water you apply to your plants), we leach every 2 to 3 weeks during the peak growing season. For us this means turning on the overhead sprinklers and running them for over an hour to flush out excess salts. This can also be accomplished with a monthly watering with RO or rainwater. When we use RO water we always add a weak fertilizer solution (25-50 ppm Nitrogen). This prevents us from leaching out too many essential minerals for the plants.
Proper watering technique
We use Dramm water breakers on our watering wands. These watering heads come in a range of styles. They are categorized by the number of holes on the head. A 400 will give larger water droplets and faster flow, while the 750 (my personal favorite) provides smaller droplets and lower flow. The result is a gentle drench that flushes the pot without disturbing the media. Holding the watering wand well above the foliage allows the small droplets of water to pick up plenty of oxygen on the way down to the plants.
Watering should be done thoroughly, to the point where it is running through the entire pot and out the bottom. The entire profile of the pot should be drenched. If you don’t flush the pot long enough the water will just channel through the edges and there will be dry spots. If in doubt, pop a few plants out of their pots after you water and examine the media. If it is soaked all the way through you are watering correctly. If there are dry spots you are not.
You can see how we water here: https://www.youtube.com/watch?v=g8Uu0W6LqIk
Soaking your plants in a tray of standing water is not recommended. No air is introduced to the root system, and that is critical. Roots need air. Also you run the risk of spreading diseases among plants soaked in the same water.
When to water
Most Paphs should be watered before they dry out completely. We generally water about once a week. When it is really hot in the summer we will water more frequently, and when we get cold rainy weather in the winter we will water less frequently.
There are some exceptions. We water Paphiopedilum fairrieanum 2 to 3 times per week as this species can never dry out completely. Conversely, most multiflorals prefer to get slightly dry between waterings. This is especially true in the cooler winter months.
If you water Paphs properly they are not difficult to grow. Most unsuccessful Paph growers simply do not pay enough attention to this aspect of culture. Paphs lack the water storing pseudobulbs of Cattleyas and Dendrobiums so they cannot buffer against stressful dry periods. Thorough, deep watering is the key to growing strong, healthy Paphiopedilum.