I think it is about 50F.

50 is the absolute lowest. I leave my phal out until it drops below 50 F. But I believe 55 F is the recommended low temp.

Do I start to fertilize at this time, after I bring it in? A complete fertilizer, or a bloom booster?

I recently purchased my first orchid. I have been doing research on it, and everything I've read says the minimum temperature is 60. I am sure people on here know from personal experience. I just wanted to pass along what I had read. I am going to try growing mine indoors and keeping the temperature above 60 at night.

That information is correct, the recommended low is about 15C. But the question was "when to bring inside" Just say the cold night was a one off and day temperatures continue to warm, then perhaps the plant might be better left outside. Lots of perhapsers in the orchid growing world.

FWIW,

I live in zone 6, been getting into the low 50's here. My phals sit under an eave so they stay a little warmer than the 'recorded' temps. I feel safe leaving them out until it hits the upper 40's for several nights in a row. A lot of hybrids like that nightime drop in temps (@15-20 lower than daytime highs) to initiate spikes. At this time of year, use a bloom booster fert on phals, but you should fert weakly/weekly all year long anyhow.

Good luck,

Bob

When I grew Phals in NY, they always began to spike in Sept. I left them out until the night temps 'held' under 55F. A few cool nights never hurt them.

This is my first year living in Fla. and I have no idea when the temps drop. It is still so warm and very humid. I only have 2 phals left, as the others rotted away over the summer. Not an ideal environment for Phals. They seemed much happier up north!

Jane

Jane, you are looking at the very end of Nov at the earliest. Of course there can be a cold front come in for a few days during the winter. I used the Tampa area for your average temps chart.

Here is a link that might be useful: Tampa temps

The dance has started...
Got down to the mid-upper 40's here Saturday and Sunday night, so I brought in my 15 violaceas and violacea crosses. Supposed to be in the low 40's here the next 2 nights, so I'll bring in the rest of the warm growers (@30 phals/others) this evening. Warms back up later in the week and then drops into the mid-40's again this weekend, gonna be fun hauling 'em in and out for the next few weeks. Plus, I'm only on week 2 of a 3 week bug treatment plan, so I need to get everything out for at least one more good dunking/spraying of Bayers before bringing them in for the winter.

Bob

Orchids and all house plants that are outside for the summer should be brought in the house before the furnace is turned on.
Bill