I have been at growing orchids for only 14 years. I have worked at a nursery for several of those for fun and I have learned a few things on my own and at the nursery.
OK,back to the topic. If you import, you know that many plants come in rootless or with very little roots. If you over water and have little air movement you might get rootless plants at home.
it's good to know what caused your roots to die or rot. Most of the time it's root rot. Root rot is when a plants roots can not exchange the gases it needs to and a build up of carbonic acid rot the roots. it's not the fact the plant gets too much water but the fact the medium stays to wet or brakes down to the point where good air exchange is no longer possible. This is why many plants can grow in water culture or hydroponically, stay constantly wet but because the water is changed or the water gets poured through it allows for a good gas exchange and the roots never rot.
OK, a good remedy for getting roots to grow is called Sphag and bag. I personally have never done this but the main point is to not water but give the plant a high humidity situation. I can do this in my GH, but a problem with the bag part can be fungus and mold. A little physan(or other fungicide) and opening the bag everyday will help out.
So, once I started with a sugar water mixture to give all my rootless and imported plants a jump start, my success rate soared. here is what you need:
First, I spray all plants with a fungicide and let dry. Then I put in this mixture
1 gal warm water.
1/4 cup sugar
a rooting hormone (I have personally used Superthrive or schultz's rooting hormone and they work well)
You can add 1 tbs of vitamin E oil if you can find it but it's not necessary
I let the plants soak for 3 to 5 hours in the product. Then keep the plants in a humid environment. Sphag and bag, on a bed of Sphag in a GH or another way to keep the humidity high without constant watering. Usually rootgrowth happens in about 2 weeks. Some species earlier and some later.
There might be many other recipes out there but this is the only one I know and it works very well for me.