Unstable atmospheric conditions may be the biggest cause of failure in cloning by novice gardeners. Some plant varieties are resilient and will not be adversely affected by large temperature or humidity swings. However, many plant varieties require uniform atmospheric conditions during the initial rooting stage.
A temperature range of 70-80 degrees F for clones is generally accepted. If this is not possible in your greenhouse or indoor garden it may be necessary to create a small sub-climate elsewhere. Uniform temperature is probably the single largest factor for cloning success. If the temperature gets too hot, the clones will wilt and die before creating roots and if the temperature gets too cold, the clones will enter a state of suspended animation and never create the root systems they need to become individual plants.
Seedling heat mats are a great way for horticulturists to maintain the proper temperature during the cloning process. Humidity is also a large contributing factor to successful cloning. Many plant varieties do best with a high humidity (80-99%) during the beginning stages of cloning.
The cutting, once removed from the donor plant, has no root system to bring in moisture. It is, however, able to lose moisture through the surface of its leaves. This makes the cutting rely heavily on the moisture in the surrounding air to maintain health, especially for the first few days. Humidity domes or humidity chambers are great ways for a gardener to maintain a higher level of humidity for the initial stages of cloning. Generally speaking, it is a good idea to acclimate the clone to the ambient humidity after three to seven days. This can be done by taking off the humidity dome each day for a few minutes and then increasing the duration of removal each day.