The roots will draw whatever nutrients are available, whether it's from potting material or something dissolved in the water you use. Some media contain no nutrients: S/H, clay, expanded shale, etc. Some do: bark supplies nitrogen, sphagnum moss supplies a range of nutrients, but in small amounts. You still need to fertilize.

Bloom boosting ferts are high in phosphates the second number of the three listed on the label: ie, 10-30-10 That's nitrogen-phosphate-potash. Bloom boosting ferts shouldn't be used year round however. They're not a good long term balance for an orchid.

Many things can trigger blooming; temperature drop, day length changes, proper light levels, as well as the correct nutrients. Sometimes the addition of trace elements can push a stubborn plant into blooming. It's not simply a matter of fertilizing, but certainly fertilizer helps. Too much can burn a plant's roots and leaves, however. It's a matter of experience learning which ones are heavier feeders and which ones aren't.

I figure a blooming size plant should flower for me within 16 months after I acquire it. Sometimes a change in conditions will set a plant back for a few months, and different orchids bloom in different seasons. If, after 16 months, it hasn't performed, then I start tweaking its conditions, because it clearly isn't happy.

I grew my collection pretty quickly last spring and summer, so I'm looking forward to a lot of new bloomers this coming spring!

McJulie