Fertilizer. To explain the whole "why" would be an exhausting book length essay, a massive undertaking even for me, who normally posts in book length essays. I'll focus on what I do and explain why later, or elsewhere or maybe not. I've been promising to do a full blown article for at least 4 years, still haven't done it. Michigan State University did nutrition studies for producers of potted plants in synthetic soils. The whole bedding plant industry relies on some of the research done at Michigan State. MSU for short. Jan Szren (yes, 4 consonants and only one vowel), developed a modification of the MSU plug plant formulation idealized for the orchid collection at MSU. The formulations are published for public domain. I contacted a fertilizer manufacturer, and had them make up the following fertilizers for me. I sell enough fertilizer at my orchid talks that every 18 months I have them make another large batch for me. (minimum order is over 1000 pounds for the custom blends) If anyone wants these fertilizers I sell them in one pound and 2 pound containers, or 25 pound bags. Contact me via PM if you are interested.
What do I actually use for fertilizer?
I use MSU Formula Orchid Special modified to deliver lower Potassium - MSU K-Lite for short. Current formulation is 12-1-4. This formulations supplements calcium and magnesium as significant macro nutrients. Because calcium is present there is no sulfur in this formulation. It is a liquid soluble inorganic fertilizer, with a very complete list of macro and micro nutrients. I use this for my orchids, bonsai, tomatoes in the garden, for any green plant that needs to get fertilized. EXCEPT blueberries and extreme calcifuge plants like Sarracenia and Drosera.
For the Blueberries I use the MSU Blueberry Fertilizer it is 11-2-6. It is a water soluble all inorganic fertilizer where 100% of the Nitrogen is as ammonium ion, no nitrates or urea. It also contains a goodly dose of sulfur, manganese and iron.
For ALL my ''regular'' plants, bonsai and orchids I will fertilize with MSU K-Lite at least once a week, usually a low dose for 2 or 3 waterings in a row, then one watering that is just plain water, then one watering that is Blueberry 11-2-6. Then return to 2 or 3 waterings with MSU K-Lite. Most of the time I consider my Satsuki azaleas ''regular'' plants, but in summer I keep them near the blueberries, and they get hit more frequently with the blueberry formulation. They seem to respond well. In winter they are kept with the not quite cold hardy bonsai. and get the ''regular'' treatment. Blueberries are dormant in winter, usually get no fertilizer.
Note - I tend to use a low dose frequently, 70 ppm as N is my normal dose, depending on which formulation we are talking about this is about 1/2 teaspoon per gallon or 2.5 ml / 4 liters by volume. This is a light dose.
I prefer inorganic fertilizers as they do not attract racoons, squirrels, mice, rats, dogs, cats or other pests. They also do not plug up the pore space or air voids in the media.
Why lower potassium? My orchids are in a continuous feed situation, and most fertilizers that supply the bulk of their nitrogen as nitrate, the amount of potassium is roughly equal to the nitrogen. In a continuous feeding program, the potassium can accumulate to an unacceptable level. Potassium becomes an environmental toxin in aquatic systems at around 40 ppm. Myself and a number of other indoor orchid growers were seeing problems with excess potassium, so Rick Lockwood in 2013 developed (published) a modification of the MSU formula, K-Lite and I have been using it ever since. K-Lite is not ''absolutely'' necessary if plants are watered with clear water between waterings with fertilizer. So the need for K-Lite really only applies to indoor and greenhouse growers who are fertilizing every time they water. Hydroponic growers too. But it is a good formulation, and what the orchids eat, everybody eats. I love the color of my pine needles and the blue of my spruces if I'm on top of fertilizing. (I admit this last 2 years many more waterings than usual were clear water, getting lazy).