On a forum, there was a discussion about how to define if the orchid roots are good or dead. Many flower gardeners believe that you can spot the difference by looking at the tone of the root colour. Like the live roots are light and the dead ones are dark!
Looking back at my personal experience i wouldn't recommend you to follow such a method. There are many plants that originally have a dark brown root colour.
Here is a very common mistake of amateur gardeners: they think that a light-coloured root is alive. But then they cut the root and see that it's dry and hollow inside.
Sometimes you notice that the roots placed in the deep part of a growing medium get a yellowish or even brown tone. The reason is that it's too dark for the roots, moreover they can be affected by the matters that your plant receives from the soil. In this case the dark tone of roots doesn't show that your plant is getting health problems.
If the root is tough we can say it's healthy. And other way around, if it looks healthy at the first sight but you can easily press it in with your finger or nail, most possibly this root is already dead.
Sometimes a necrotic area of the root is so small that you can't immediately see it. Your orchid doesn't need such a root anymore, because it's unable to nourish the plant in full value. Also a necrotic part of a root can infect the orchid stems, so please be very careful when inspecting roots.
It's a mistake to count that if the green part of your orchid seems normal, then its roots also feel good. A pathogen process inside a root doesn't happen instantly. As earlier you find a root problem, the more time you have to save the orchid.
First of all, correct the mistakes you have in taking care of the plant. It's only possible to bring the orchid back to life if you create the ideal environment for it. To form а new root system your plant uses sprouts, that pop out of green healthy buds. To find these green buds is your very first task.
Moisten the roots of an ill orchid daily with water. Just put the plant inside a bowl and place near or at the window. Every morning add water in the bowl in the way it only covers a rhizome. The orchid needs to take this bath for about 1-2 hours, although it won't hurt if you leave it there for a longer time. The optimum air temperature for this procedure is 20°C.
To awake the sleeping buds on the orchid, try to give it a growth stimulation bath. A water epibrassinolide solution for example (one drop of stimulator in a glass of water). Watch out, the orchid can take such a treatment only once in 14 days.
It's a matter of luck. One has it back to life in a month, sometimes it takes a year, another time it is not even possible. Your chances on success will be doubled when the intensive cure period is taking place during Spring or Fall.
The first moment you see new roots, stop providing the plant with extra nutrition. Normally, if the fresh healthy roots have appeared they will grow their power, getting stronger every day. Once the length of new roots is 5 cm or more, put the plant in a pot, but keep in mind – you need to avoid over watering. The soil needs to have enough time to dry.
My advice is to use small and medium fraction conifer cortex and clean Sphagnum moss with an addition of crushed charcoal.
After the orchid is put in a new pot you will need to secure it, to be sure the fragile roots won't get broken. To do so, force two sticks into the growing medium and tie the plant to them.
There is one more way to reanimate an orchid, called the hothouse method. You can either buy a glass-house or make it yourself from a fish tank or plastic bottles.