Photography credit: José Manuel Suárez
We take water for granted. It falls out of the sky. It flows from the faucet. Oahu city water is considered good for growing Orchids. We use it without thought or concern.
If you study orchids in their natural environment, you’ll notice several things. They do not grow in pots, and certainly not in plastic pots.
Most Orchids are epiphytes and are adapted to pristine growing environments high in the upper canopy of the rain forests. They never get fertilized by humans and never irrigated with city water, just rainwater and morning dew. Their root environment is airy and free of minerals. Humidity is always near 70%.
We tend to focus on media components. We always look for the best fertilizer. We study and teach the best growing techniques for repotting and caring for our precious plants. Little is said about water and how to apply water to our plants. There are no water experts to help us. So, I will cover a few basics.
After 45 years of growing Orchids, I have read most of the Orchid culture books and magazines. The best article is by Dr. Bill Argo (see Reference 1). Water quality determines everything we do. I have talked to many good Orchid growers. I have notes and have tried many different styles of growing. Most of the different styles did not harm the Orchids but did not help them grow better. Over time, much time, I began to notice patterns on the island of Oahu. The best growers were deep in the valleys of Manoa, Nuuanu and Palolo. Up in the heights like St. Louis Heights, Aiea, Pallisades, Mililani, and Wahiawa also. The clusters of good growers in Hilo and the island of Maui are at about 1,000 feet elevation. The hobbyists at sea level, especially on the leeward side, are the poorest growers. Why?
The answer turns out to be the water the Orchid receives. On the windward side of Oahu, the rainfall, the temperature, and humidity are superior. If you are close to the Koolau Mountains and at higher elevations, the rainfall, humidity, and cooler temperatures are perfect for your orchids. At over 500 feet elevation, morning dew is ever present year-round. Succulent Orchids with thick leaves and bulbs can survive on dew alone.
The poor areas for growing Orchids are Hawaii Kai, Kaimuki, Kahala, Salt Lake, Ewa, and Waianae. Low elevation, low rainfall, low humidity, higher temperatures, and no morning dew are difficult challenges to overcome. I recommend you move to Aiea Heights near Mel Waki. If you cannot move, read the following paragraphs carefully. I will give you the adjustments needed to succeed, with city water.
We pot our plants in plastic pots. Every grower uses a different media. After a certain amount of rainfall, the plants become 
waterlogged. A dense potting soil and plastic pots are dangerous. If you cover the plants with a plastic roof, you can control the water going in the pot but the humidity tends to be too low and the temperature higher. If you collect the rain and apply it evenly, as needed, everything is great. If you discard the rain and use Oahu city water, the minerals in the city water tends to accumulate in the media. To flush the excess minerals, you need to irrigate with a sprinkler for a minimum of 12 minutes. That is a lot of water. If you use a hose and water breaker, you must apply a large amount. My favorite mentor, Wilbur Chang would advise, “The important thing is that water comes out the bottom of the pot. A good watering is three passes in a session. You don’t have to water every day. Skip as many days as you can until the media in the pot is dry.” The city water has mineral ions that tend to accumulate on the roots and in the media. Only a good watering will keep the mineral content low.
So, what’s wrong with being near sea level and on the Leeward side? It is the low humidity and higher temperatures that stress the plants and force growers to irrigate more often. The lower humidity will also cause more of the minerals to dry and adhere to the roots. In the mountains and deep in the valleys the temperature is cooler and morning dew is always present. There is a huge water advantage for valley and mountain grown Orchids.
Here in Waimanalo, H&R Nurseries being at sea level irrigates frequently because of our low humidity and high temperatures. If I get any rain or a rare morning dew, I can skip a day of irrigation. If I water lightly to raise the humidity, the minerals in the city water will hurt the roots. So, I refrain from wetting the plants with city water. If I had rainwater, I could water lightly to raise humidity with no pilikia (trouble). Rainwater is our most under-utilized resource available to most of us.
Tanya Lam of San Jose, California shared with us an excellent program on how she grows her beautiful Orchids with rainwater. There is 
little rain in San Jose and during the summer the humidity can be as low as 20%. San Jose water is full of minerals that can hurt the Orchid roots. Since rainwater is pure with no mineral salts, she can apply very little with good results. So, every Winter she collects 11,000 gallons to supply her large collection during the hot Summer months.
I cannot imagine many Hawaii people with that kind of dedication. But how about collecting rainwater in 45-gallon trash cans and using it as a supplement. Another way is purchasing a Reverse Osmosis unit which makes pure water using a special membrane. For $125, you can purchase a small 100 gallon per day unit. Just hook it up to a hose and it will make about 100 gallons of pure water. (A small water sump pump connected to a ¾ inch hose for watering.) Remember, you need very little of this pure water to irrigate your plants. It is as pure as rainwater. Use it to raise humidity. No drenching necessary unless you want to. I grow in the rain with shade cloth. So, the pure water is a supplement during the summer months with no rain and little humidity.
Today, I grow my plants at sea level almost as well as the best growers on Oahu. Most of my success over the last 10 years has been adjusting how I water. I follow the recommendations from Richard Takafuji. Most of the nursery get 12 minutes of irrigation with city water, as needed. That’s a lot of water. My hanging plants and Vanda are now getting 20 minutes of irrigation once per week and 12 minutes twice a week during the summer months. Of course, I skip on days that it rains. Thanks to Tanya Lam’s program, I started to use small amounts of rainwater and Reverse Osmosis water to raise humidity and the results have been fantastic. I wish I had started this 45 years ago.
Happy Growing!
Roy Tokunaga
References:
1. Dr. Bill Argo; Five Part Series on Water and Media, Part 2: Water Quality. http://www.staugorchidsociety.org/culture-water.htm.
2. J. R. Peters; ‘What’s in Your Water?’ 2012. Orchids 81(5): 304-307.
3. Bottom, Sue and Tokunaga, Roy. 2017. Choosing Fertilizer Based on Water Quality. Orchids 86(2)108-116.
4. Taiz, L, and E. Zeiger. 2015. Plant Physiology, 6th ed. Sinauer Associates, Sunderland, Massachusetts. Chapters 3 and 4. Water. Pages 37-70.
Roy Tokunaga’s Email Address: greenthumb808@aol.com