Basic Phragmipedium Culture
Phragmipediums are a mostly South American genus of lady slipper orchids, though some are found as far north as Mexico, and also have cousins called Mexipedium and Selenipedium in North and South America. They differ from Paphiopedilums, which are more common and more-often hybridized, in a couple ways: Phragmipediums are generally larger, grow in brighter and moister locations, and tend to have sequentially flowering stems that can continue for many bloomings.
Unlike Paphiopedilums, Phragmipediums are often growing in rather bright spots at the edges of forests and along streams, in environments closer to Cattleya light. When first introducing your plant to your home, it’s generally best to pick a spot that’s bright, indirect light (approximately 2000 footcandle) and gradually increase to somewhere with direct sun in the morning or afternoon for about four hours total (not summer midday sun, and less than 3000 footcandles of intensity). Since most of the deeper colored plants are from mountains which don’t get as hot, these plants can tolerate brighter light when the air is cool and their leaves don’t build up heat.
Temperature & Humidity
Phragmipediums can thrive between both cool and warm temperatures depending on their backgrounds. Plants descended from higher altitudes tend to prefer cooler temperatures, and notably, flowers tend to develop much more intense color if their temperatures stay below 80 F. Many plants will tolerate up to mid 90’s F without much fuss, but sustained heat and warm nights can eventually hurt the plant. The lower limit for many Phragmipediums is 50 F during the winter nights, but staying warmer is generally safer and easier to handle, since the humidity can rise fairly high at cool temperatures and increase the chance of fungal infection when leaves stay wet at night.
Ideal humidities are between 60 -70% relative humidity. If lower, make sure that the pot doesn’t dry out. At higher humidities, add air movement and fresh air often to prevent mold.
Like other lady slippers, Phragmipediums are terrestrial growers, mostly, and the majority do best in a moist, free draining mix. Common potting media include a fine or medium orchid bark mix, as well as pro-mix with bark, perlite, or grit and sand. Since the majority are found along stream beds of pure mountain spring water, it’s important that the mix stay moist and be light enough for the roots to spread, and potting into a mostly sphagnum moss media tends to damage roots very quickly.
If the humidity is too low, it helps to have the pots sit in a saucer with an inch of water to prevent drying out, and terra cotta pots help wick water up as well as keeping the roots cool during hot days. When keeping standing water in contact with roots, you’ll need to make sure to replace and rinse water through the pot at each watering; keeping the water and letting it sit promotes bacterial growth as well as causes salts to build up, so rinsing helps keep things clean.
If you are interested in hydroponics, you can grow Phragmipediums using a clean, low nutrient hydroponic system. Some of the simplest systems are plants potted in clay pebbles and sitting in distilled water.
Water & Fertilizer
Though Phrags are fairly terrestrial and like moist roots, they don’t handle decayed potting media very well, so most people tend to repot every one or two years. If you have well water with high mineral content, yearly might be a better option to prevent salt buildup and root burn, or in case the leaf tips start to brown. Repotting should happen when the new growths and leaves are emerging, and any divisions that are made should have at least three or four mature growths and one new growth.
Fertilizer should be mixed at half or quarter strength compared to houseplants, and applied once per month, year-round. Since these plants don’t have a rest period or dry period, keep fertilizing during the winter, but possibly at a lower rate if the light is weaker. If you alternate between high nitrogen fertilizer for growth and a high phosphorus fertilizer for blooming, switch around late winter, since most plants tend to bloom in the spring and too much nitrogen can lessen blooming. If the summer is hot, consider stopping fertilizing during July and August so that the plant doesn’t absorb too much fertilizer while it’s drinking water to cool down.
Brown leaf tips are generally a water issue, most commonly from water that’s too high in dissolved minerals, fertilizing too often, or when the pH is too high; alternatively, it can also happen when the pot and roots dry out often. In these cases, the simplest solution is to stop fertilizing and switch water sources to either distilled or rain water and keep the pot sitting in a little water. If new leaves start to also brown at their tips, you may need to switch potting media to something fresher or with a balanced pH. If the fertilizer is causing problems, then consider hydroponic fertilizers instead, or water with clean water 30 minutes after fertilizing to rinse off the fertilizer that hasn’t gotten absorbed.