Stanhopea Water Requirements

Many Stanhopea require copious amounts of water during the summer months here in southern California.  I usually water three times a week from spring to fall and once a week or not at all during the winter depending on the amount of rain received.   I water more frequently during the summer and early fall when hot weather is expected (above 85°F or 29.4°C). I water and mist the plants every day if temperatures are very extreme (above 95°F or 35°C).  Several Stanhopea prefer lower amounts of water during the winter and often require this to induce bloom the following spring and summer.  The Stanhopea that benefit from this reduced watering treatment include (S. hernandezii, S. insignis, S. jenischiana, S. lietzei, S. maculosa, and S. martiana).

 I usually begin to reduce the water for the above mentioned species in December and continue until new growth begins (usually April).  I reduce watering by approximately 30-40 percent of what the other species are receiving.  This usually means that each week I skip one watering application for the above mentioned species to allow them to dry out a little more than the others.  This doesn’t mean that I allow the growing medium dry out completely.  Most Stanhopea cannot tolerate the medium drying out for extended periods of time.  An overly dry growing medium could also damage mature leaves, new growth, and roots of Stanhopea.  Therefore, you only need to allow the medium for these species to dry out slightly but not completely.

Stanhopea insignis with a low pressure stream
bubbler used to water during the dry season.

Water quality is a concern of mine and I choose to grow certain species of orchids for that reason.  I have tested my water that is delivered by the city of San Diego water department and found the pH to be high – 8.2, with total dissolved solids at 337 parts per million (ppm), and sodium levels at 74.2 (ppm).   This means is that the pH of the water and dissolved solids is high enough so that it is not conducive to grow several species of orchids that require neutral pH and lower dissolved solids. High levels of dissolved solids usually leads to stunted plant growth, and build up of salts in leaf tips.  You should also fertilize more frequently but with reduced concentrations of fertilizers when using water with high dissolved solids.

I was faced with two choices for growing a large collection of orchids, either grow orchids that would tolerate these water conditions, or buy an expensive reverse osmosis system and pump to supply treated water to the orchids.  I chose to grow orchids that would tolerate the water quality from my city water supply.  I selected Stanhopea because they had proved in the past to be relatively tolerant of poor water quality and could be easily grown outdoors.  The list of orchids that would grow under these conditions was long enough to make the decision difficult.  These other orchid genera include Encyclia, Cattleya, Cymbidium, Sobralia, and Zygopetalum.  Many of these genera require more sun and a good portion of my growing area is shaded throughout the year.  Several of the above mentioned genera  grow very large and would take up even more space than Stanhopea.  Therefore my choices were reduced enough to settle on growing Stanhopea.

My plan is to eventually obtain a reverse osmosis system for my orchids over the next few years, but until that time Stanhopea grow rather well without it.  The reverse osmosis system would allow me to grow much healthier and well grown plants in the future.  I currently have 53 Stanhopea in my collection and the collection keeps growing every year.  This size of an orchid collection makes it difficult to use another source of pure water (rain water) to irrigate the orchids, but I do collect enough rainwater in the winter to flush the baskets at that time and remove built up dissolved solids in the growing medium and sphagnum moss that I use to line the baskets.  The size of my collection and my work schedule also preclude me from hand watering the collection.  For now I am using the municipal water system and the Stanhopea tolerate the water quality quite well. The orchids tolerate this poor water quality because I soak the basket and growing medium once a week, thus leaching the dissolved solids out of the media to prevent build up.  There is some accumulation of salts in the oldest leaves of some Stanhopea species that cause unsightly brown leaf tips on a few leaves.  This usually occurs more frequently just prior to the leaf excising and falling off, so it is not a long term unsightly issue.