It is possible that they have gained pests of some kind overnight, but then they may not have done, it's impossible for anyone to say! Pests can fly, jump, crawl and move around, even house plants can be pest magnets so no plant can ever be deemed to be pest free. It takes one greenfly to invade a plant, they breed at an astonishing rate, even the newborns are born pregnant! The soil you planted them in is full of microbes and innumerable potential pests, nothing is guaranteed. Have plants and you will have pests at some point in time.

Gill UK

Many ppl never take plants outdoors and they get 'nasties' like mealy bugs, scale...There is no sterile environment (well, in the lab there could be :). Check the 'cleanest' soil with good microscope & you'll be surprised how much life is there. And then, there are many beneficial bugs too.

The best defense against pest infestations is healthy, vigorously growing plants. While it certainly depends on the plant and your climate, for many plants it is much easier for them to grow vigorously outside, thus reducing infestations. Personally, I have only dealt with the most annoying pests (spider mites and mealy bugs both in my case - not yet dealt with scale - knock on wood ...) indoors during the dry winter.

The one exception has been powdery mildew, which zinnia's seem to always get - and it can easily spread (to my wisteria, in about a day, and then a japanese maple - ouch!). I will never grow zinnia's again. pretty, but not worth the pain.

I rather deal with scale than mealy or thrips or spider mites - they are easier to spot early and spray of alcohol+water will take care of them.

prettypots1, can you post a picture? That way we can determine whether they would be better outdoors or in...