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THis is the Pelican Parts of the Orchid world. Beginner Discussion - Orchid Board - Most Complete Orchid Forum on the web !

I've converted most of my orchids to "semi-hydro" or "s/h" or semi-hydroponics. For me, it's much easier.

This guy invented it. https://firstrays.com/free-information/basic-orchid-culture/semi-hydroponics/
That guy is active on the bulletin board that I posted at the top of this article. He's an engineer that's been doing the orchid thing for something like 20-30 years.
This is a great list of how to get it going.
https://firstrays.com/semi-hydroponic-culture/sh-detailed-information/
From his site, this is roughly how mine look. I then keep the plastic pots in decorative pots.



I am using restaurant soup to go containers, leca from Ikea and

THis is how I figured out the fertilizer.

If you're looking for 25 ppm N (Nitrogen) with a fertilizer with the first number of 13, for example, that means you want 25mg N per kg (liter) of water in the final solution. As the powder is 13% N, that means you're shooting for 25/0.13=192 mg of fertilizer powder per liter. But that's kind of tough to measure, so we should make life easier and make a concentrate in which that much is contained in a smaller volume - for example, let's say we want that in 10 ml. 192 mg/10ml = 19200 mg/L, so of you put 20 grams in a liter, that's close enough, and 10 ml of that solution, diluted to 1 liter, gives you your ~ 25 ppm N solution for feeding.

I mixed up a batch of strong fertilizer in an old 1 L water bottle. I then used 10ml of that per liter of water for watering. It's super dilute by then. The liter of strong stuff lasts a long time.

This is more info from the other board.

Originally Posted by Ray
Being an engineer and bit of a nerd, I started delving into the nutritional needs of orchids, and it actually opened my eyes significantly. (Warning! Professorial mode: On)

If you look at the makeup of an orchid, it is 95% water. Of the remaining 5%, about 95% of that is carbon, oxygen, and nitrogen, with the first two coming from water and air; the N it gets from the fertilizer we apply. The remaining fraction of a percent is the rest of the stuff it gets from fertilizer.

Add to that some analyses of the water that drips down on orchids in the wild (their primary source of nutrition), and we see that it is almost devoid of any nutritional value - 15-25 ppm total dissolved solids (TDS) is typical, and that's only when it just starts raining - and we learn that most of that is nitrogen.

So my conclusion from that is that nitrogen is the most important nutrient, but it should be applied very sparingly, as 1) the plants have evolved to need very meager nutrition levels, and 2) excessive N can actually stifle flowering.

I won't go into details (look up "Rubisco" if you're a bit of an intellectual masochist), but in order for any plant to add about a pound of mass - a huge amount in orchids - it must absorb and process about 25 gallons (roughly 95 kg) of water, but only about 5 grams of nutrient elements.

So, about 7 or 8 years ago (I've been growing orchids for over 45 years now), all of that led me to this growing regimen:

Use a VERY open potting medium, so the roots always have excellent air flow around them.
Water the daylights out of them: Frequent & Flooding. Water is the driving force behind plant growth.
Use a very small amount of fertilizer at every watering. I mean really little. Divide 2 by the %N on the labels to get the teaspoons per gallon to use.
Make sure that "fertigation" solution contains nitrogen, calcium, and magnesium; the other stuff can "tag along". (Your water supply may have enough calcium and magnesium in it, but as a user of RO water, I add it.). I prefer K-Lite, a 12-1-1-10Ca-3Mg derivative of the MSU RO formula.

All of my plants seem very happy with that, and are growing and blooming better than I've ever seen - figures it would take me almost 40 years to figure that out....

When the MSU fertilizer was first released, the developers recommended 125 ppm N for feeding. Figuring they knew what they were talking about, that's the level I used. Later, after doing some research, especially that related to the analyses of the "through fall" and "trunk flow" that orchids to see in nature, and the frequency with which they are fed in nature (whenever it rains), I dropped my concentration to 25 ppm N, and started applying it every time I watered. In later conversations with the PhD that led the development team, he told me that there was no scientific basis for the 125 ppm, but they "tried it, and it worked," so that's what they recommended.

As far as the concentration is concerned all you have to do is a simple mathematical fraction:

2÷13 = 1/6.5, so 1/6 teaspoon/gallon is fine, as is 1/8. Rounding up or down a bit isn't going to hurt anything. By the way, for those of you civilized folks on the metric system, 2.3/%N on the label gives you the ml/L for 25 ppm N.

Something I would recommend to everyone however, is to make a concentrated stock solution, and then use a bit of that solution to let down to your final fertilizer concentration. Many fertilizers, the original MSU for example, are very heterogeneous. Each ingredient is a large flake, small flake, powder or prill, so taking a fraction of a teaspoon or ml and expecting it to be true to the fertilizer formula is questionable. Add to that the fact that powder bulks densities can vary greatly, and it is folly to try to measure them by volume, hoping it equates to mass.

Instead, I recommend that folks make up a concentrate with a larger, known weight of powder. If you're looking for 25 ppm N, for example, that means you want 25mg N per kg (liter) of water in the final solution. As the powder is 13% N, that means you're shooting for 25/0.13=192 mg of fertilizer powder per liter (or 192 x 3.785=728 mg per gallon). But that's kind of tough to measure, so we should make life easier and make a concentrate in which that much is contained in a smaller volume - for example, let's say we want that in 10 ml. 192 mg/10ml = 19200 mg/L, so of you put 20 grams in a liter, that's close enough, and 10 ml of that solution, diluted to 1 liter, gives you your ~ 25 ppm N solution for feeding.

For Imperial measurers, 0.2 pounds of that 13% N fertilizer, when used to make up a gallon of concentrate, allows you to use one ounce to make up that same gallon of 25 ppm N final solution.

Steve, I believe it has been stated already, but fertilizer is probably the least important aspect of orchid culture.

Feed lightly and regularly, and dedicate your time to making sure ALL of the other aspects of culture are correct

I also asked in a PM about "flushing". If you aren't aware (I think someone mentioned it in an earlier post) with heavier fertilizer it can build up in the media and pot and cause problems with the plant, so you occasionally need to use just plain water to wash out some of the stuff that's building up.

What Ray told me about flushing was that if I was fertilizing at 25ppm and using a LOT of the liquid, then I was essentially flushing with every watering so you don't need to do the occasional flush.

I just had 4 orchids rebloom, 2 Oncidium orchids and 2 Phalaenopsis orchids. All 4 appear to be pretty healthy. I have a Cattleya that I almost killed by over fertilizing before I found the other forum. I have another that has several new pseudo-bulbs popping out, but no new flowers yet.