Dave did a good job on the mycorrhizal fungi response, so I'll try to address the fertilizer question:
There isn't a "best" fertilizer. Here's why I say that:
- Plant nutrition requirements vary from plant to plant, so we would potentially need a formula specific to each one.
- The nutrition includes whatever minerals are dissolved in your water supply, furthering the need for a zillion different formulas.
- Temperatures and light levels can also play a role in nutritional needs.
That said, I believe that there are a general set of nutrients that all of our orchids need, so choosing a fertilizer that is complete with all of the known macro-, micro-, and trace elements is a good idea, but avoid one that's really high in nitrogen, as that tends to give you wonderful foliage, but no flowers.
I have been using the Greencare "MSU" formula at every watering for the last 3-4 years and am very happy with it. It's ratio's are similar to the MaxiGro stuff. I used Dyna-Gro "Grow" formula for years, and was happy with that, too.
Another thing to consider is concentration. Think of it in human terms: eat a complete-but-small meal a day and you might survive, but will not thrive. Increase the quantities and you'll be a far healthier individual (let's not go to the overfeeding part of the gradient, that get's too personal).
Fast-growing plants need more food than does a slow grower. Those in active growth need more that those that are resting. Because I have a varied collection of plants that are in every conceivable stage of growth and blooming (or not), I go with the general concentration recommended by the MSU study, about 100-150 ppm N at every watering.
If I lived in Florida or Hawaii, where the temperatures and light levels are higher, I'd probably increase that rate.
Then there's the pH, which can affect nutrient availability and uptake...
If you want to learn more, Dr. Bill Argo, inventer of the MSU formula, sent me PDF's of his 5-installment article about plant nutrition, and I have it on my website:
Plant Nutrition
Hybrid Mode
