Feeding your orchids

[raybark]

Over the years, I have focused a great deal on the science behind feeding my plants, and more recently done a lot of studying related to nutrition in epiphytes, which, it turns out, is a lot different than that in terrestrial plants.

There are lots of debates concerning formulas, the sources of the nutrients, and the like, but I have come to the conclusion that fertilizer is very low on the orchids' "Maslow Hierarchy". How many times have we heard "My grandmother NEVER feeds her plants, and they bloom beautifully."?

The plants are approximately 90%-95% water, so maybe that should be the primary focus.

I think that the best thing we can do for our plants is grow them in a manner that permits VERY frequent watering (mounting, therefore is #1, closely followed by basket culture with minimal or very open media; it explains one of the benefits of semi-hydroponic culture, too, if you must use a pot), and the use of pure water with only a trace of nutrient added.

With no exception, people switching from mineral-laden tap water to pure water always remark at the improvement in their plants. "They just look brighter and perkier" (if that's possible). At the Alamo OS speaker's day last Fall, Harry Phillips (Andy's brother) made it a point to stress that RO water is the best thing you can do for your plants.

Then, if you add a tiny amount of a complete fertilizer - orchids in nature see something on the order of 15-25 ppm TDS, roughly equivalent to about 1/4 teaspoon of MSU fertilizer in 400 gallons - and water very frequently, you're probably going to see the best growth.

For the record, I am not advocating that little fertilizer - I now use about 35 ppm N, which is about 1/4 tsp (of K-Lite) per gallon, yielding a TDS of about 250-300 ppm, but I am unable to water every day. If I was, I'd probably lower my concentration by another 50%-67%.

Back when I was first developing the S/H culture technique, I purchased 300 each of Oncidium Sharry Baby and Phalaenopsis Lemforde White Beauty in flats, and they all went into S/H culture. Half of each were fed and watered twice a week, the other half DAILY for 6 months. The "daily" group were significantly bigger at the end of the experiment. I attributed it to them getting more food, but in retrospect, maybe the "more watering" part was more important.

I have also had discussion with folks who claim that even if you only feed infrequently (as opposed to the "every time" mode I employ) the rate of plant growth is directly related to the frequency of watering.

[tucker85]

Excellent information, as usual, Ray. I do believe that a rapid wet/dry cycle (frequent watering and fast drying) is the best way to grow any orchid that has a prominent pseudo-bulb. Unfortunately indoor, windowsill growers have a difficult time achieving that type of culture so they need to adjust their techniques to fit their environment. Needing to work for a living can also make it difficult to water frequently.

As far as water quality, I personally believe that there are five macro-nutrients rather than three. If a grower uses pure water on orchids, I believe it's important to provide Nitrogen, Phosphorus, Potassium, Calcium and Magnesium (and small amounts of micro-nutrients). The reason Calcium and Magnesium are often excluded from fertilizer formulas is that those two elements are present in many, maybe even most, municipal water supplies. Cal/Mag fertilizers are very important when using pure water. I totally agree with the frequent use of low concentration fertilizers. Fortunately I grow my orchids outdoors in open wood baskets or on mounts so fertilizer accumulation is never a problem.

[raybark]

I absolutely agree with your chemistry comments!