What is a good recipe for orchid watering and feeding?

Answer from Derek Lowenstein

The following details are particular to my growing environment. When watering and fertilizing orchids, the following chemistry-associated parameters should be considered:

  1. What is the pH and TDS (total dissolved solids) of the water you are using?
  2. What medium are your orchids growing in? I grow overwhelmingly in LECA (Lightweight Expanded Clay Aggregate) medium. The mounted orchids and those in baskets are all watered the same way. Most of the Phragmipediums are grown semi-hydroponically and are watered with the rest of the collection. None are in bark media.
  3. Different growing media will have varying responses to the fertilizer.
  4. Soak the media with the adjusted water before applying the fertilizer mixture.

In the Houston Meyerland area where I reside, the water has a pH=7.8 with TDS=~250 ppm. These two parameters vary over Harris County and the surrounding areas. Check the water in your area. You can find a pH meter for less than $20 on the web.

I prepare a concentrate solution in 1 gallon of water to make 16 gallons of delivered product via a Hozon siphon mixer (Photo 1). It’s important not to use a hose that is longer than 15 feet or the Hozon siphon will not properly deliver the correct mixture. Open the water valve to maximum output.

The pH of Houston tap water is reduced from 7.8 to 6.6 by adding 1 teaspoon of citric acid crystals (sour salt) to the one gallon. Photo 2 is the brand I use, but there are others.

I use K-Lite fertilizer (Photo 3). It is an MSU-type mixture, low phosphorus and potassium, with enhanced calcium, magnesium, iron, etc. I add 3 tablespoons of fertilizer into 1 gallon of pH-adjusted water to provide 100 ppm N for 16 gallons of delivered product.

The delivered fertilizer solution pH can vary depending on how the K-Lite material was stored. It is hygroscopic (sucks up water) and will cause the pH value to vary as it ages and takes on more water. A properly stored fertilizer will deliver the adjusted fertilizer water with pH=5.5. My experience is that very old and poorly stored K-Lite will not lower the pH below the adjusted water of 6.6. It doesn’t seem to affect the orchids. See the article on the First Rays website. at the following URL: https://firstrays.com/orchids-and-ph/.

Keep the fertilizer in its sealed container and you should have no pH changes over time.

Photo 1. Hozon siphon.

Photo 2. Citric acid crystals (sour salt).

Photo 3. K-Lite Fertilizer.