what temperatures are too cold to ship orchids

[Ray]

Don't forget that some plants are more tolerant of temperature extremes than others, but generally, plants should ordinarily not see below about 50° to be safe, but if they are dry, they can sometimes take maybe 40° for a brief while.

Yes, heat packs are effective, but they must be used in conjunction with insulation, and there are some things to deal with when using them. My approach, for example, is to surround plants with shredded paper, wrap them in closed cell foam, and wrap THAT in sheets of kraft paper or newspaper. Then I line the box with the closed cell foam, and surround the wrapped plants with foam peanuts. Just before shipping the package, I add a heat pack or two, and away it goes.

Back to the heat packs themselves... 1) They have a limited life. I use 60-hour packs, but ship for 2-day delivery at most. 2) You cannot seal the box, or the pack will consume the oxygen in the box and stop working. 3) moisture is also a prerequisite for them working, so if I'm shipping in really dry weather I'll throw a wet paper towel in the box to increase the humidity.