One teaspoon per gallon of fertilizer!

[My Green Pets]

My Catasetinae have received two AOS awards, one an AM and the other an HCC. I use K-Lite 12-1-1 at 1/4 tsp/gal with every watering. Once a month I might switch it out for Alaska Fish Fertilizer 5-1-1 at closer to 1 teaspoon per gallon.
My plants are potted in sphagnum which I assume holds on to the fertilizer like a sponge. I might experiment with using more ferts, but things are growing well under these conditions.

[Ray]

I am “iffy” on slow-release fertilizer. I’ll admit some of that is due to my frustration with knowing how much to use.

Most people just guess or use the recommendation of the manufacturer, but that is intended for use in soils. I suppose it can be calculated:

If I use the “10 mg N” retained figure from my earlier ramblings as a weekly goal, and we have a 9-month slow release formula that is 20% N, then we need the stuff to release a total of (39 weeks x 10) 390 mg N. 390/0.2=1950 mg, so let’s just say 2 grams of pellets should be used per pot.

Then, there’s the temperature factor. That “9-month” release occurs at 70F. If the temperature (average) is different, the rate of release is changed roughly 3 days per degree. Over winter, my indoor growing temp averages right about 70, but when I move them outside, that average can be 10-15 degrees higher, so the pellets will dump their contents more quickly.

Then there’s that “exposure” issue again. Some media wick well, while others don’t, and if you’re one to allow it to dry considerably, it will take the pellets being very close to the roots for them to contribute anything to the plant.

Pot size is part of the exposure factor, too. 2 grams evenly dispersed in a 4” pot are closer together than 2 g dispersed in a 6”pot, so one would expect the plant in the 4” pot to get more of it. And that assumes identical root systems that meander throughout the potting medium.

So does that mean a phalaenopsis in a 6” pot, with 8, 9” x 1/4” roots will take up less nutrition than will an oncidium colony in a 6” pot having 50, 9” x 1/8” roots?

I’ve heard of folks top-dressing pots with the pellets, which probably helps the distribution of the nutrients, but won’t they dry out more quickly, stopping the release?

[Roberta]

I only use it on orchids that need an extra boost, like Catasetinae and Cymbidiums. They definitely benefit from "more", the "how much" isn't so critical, they can utilize whatever I give them because of their rapid and substantial growth. And it poops out just about when it needs to. So I just put a healthy pinch (or maybe what fits in the palm of my hand for the bigger pots) Not scientific at all. The slow-growing "normal" orchids I would not want to use it, since there's no control and "less" is what they want.

[isurus79]

Here's a video I did with Fred where he describes in detail how he fertilizes his Catasetums. His fertilizing regimen changes during the growing season: https://youtu.be/UR1uG3Nq1As