Garden Variety: Ice cubes can be used to water some orchids
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Tropical orchids are well-known for their long-lasting blooms and beauty, but they can also be a challenge to maintain. Because they are tropical plants, they can only be grown indoors in Kansas and are especially finicky about water, light and growing media (potting mix).
Several years ago a brilliant marketer began promoting the idea of watering tropical orchids with ice cubes. Gardeners and orchid enthusiasts have argued against the suggestion since its inception, claiming that the use of ice cubes does more harm than good to the plants. To lay these claims to rest, The Ohio State University and the University of Georgia conducted a study in which they compared the practice to watering the plants with the same amount of room temperature water. The results? Ice cubes work for watering some tropical orchids.
Orchids are a complicated group of plants. There are over 28,000 species worldwide and more than 100,000 hybrids and cultivars. The ones discussed here are the most common and widely sold orchids, known as Phalaenopsis. There are different species and cultivars within this group, but they have similar growing habits. There are the orchids labeled as an “ice orchids” and/or promoted as good candidates for ice cube irrigation. Because of this, it was also the only classification of orchids included in the research study.
The suggested rate for ice cube irrigation is three cubes per week. Place cubes directly on the growing media and let them melt. The practice prevents overwatering, which is a common problem. Some claim it also reduces the amount of water that runs off/out because the slow melting of the cube allows roots to soak up the water more efficiently.
The research study referred to above was published in the scientific journal HortScience in September 2017. Researchers used four popular cultivars of Phalaenopsis orchids. They compared the use of 3 ice cubes per week applied directly to growing media versus using the equivalent volume of room temperature water. They then compared longevity of individual flowers, overall display life of plants, amount of excess water that drained from the pot after watering, photosynthetic efficiency in roots and leaves, biomass of the plants at the end of the study, and temperature in the growing media after water/ice application.
According to researchers conducting the study, flower longevity and display life were the same for orchids watered with ice cubes versus those watered with room-temperature water. The amount of excess water that drained from the pots was the same or lower for orchids watered with ice cubes versus those watered with room-temperature water. Photosynthetic efficiency and biomass were statistically similar for both sets of plants.
Temperature in the growing media did drop after application of ice cubes but was not low enough to cause chilling injury to the roots. Because of the lack of differences in the other comparisons, the temperature drops appears to be insignificant to the orchids.
In conclusion, researchers state that ice cube irrigation is a viable method for watering Phalaenopsis orchids. There are a few things novice orchid growers should keep in mind however.
• Keep the cubes out of direct contact with leaves. Although ice cube contact is unlikely to cause chilling injury, it may cause water-soaked lesions to appear on the leaves.
• Watch how plants respond. If leaves begin to look flaccid and wrinkled, give them more ice/water. This may mean more cubes or more frequent applications. Increase the amount only a little at a time. If leaves begin to look soft and roots turn brown or black, reduce applications of ice/water.
• If the orchid pot is sitting inside another pot, pull it out and empty any water that remains in the non-draining container. If the orchid pot is sitting in a saucer, empty any water that remains in the saucer. If the orchid is in a non-draining pot, re-pot it into a pot that drains. All of this will help prevent accidental overwatering.
Light and potting media are the other big challenges to growing orchids.
For light, Phalaenopsis orchids grow well in an east window or a brighter window with a screen or sheer curtain.
For potting media, avoid re-potting until necessary. Then, use a high quality coarse bark mix labeled for orchids. If it looks like regular potting soil, it will be too heavy and hold too much water for Phalaenopsis orchids.
For other types of orchids such as Dendrobium, Cymbidium, or others, seek out specific culture recommendations.
— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.