Camellia Bud drop
The following list (in no particular order) gives some of the factors that may be the cause:
A lack of moisture is perhaps the most common cause, particularly with plants growing in containers.
When deprived of moisture, the cells forming the flower stalks may fail to develop fully.
This creates a point of weakness that may collapse after frosts or when the flower buds begin to swell in spring.
Conversely, if the soil is too wet this too can contribute to bud drop.
The aim during the growing season is to ensure that the plants do not become too wet or too dry.
Wild fluctuations in winter temperatures can be a contributary factor.
Freezing temperatures can cause buds to drop before opening, especially with young plants.
Some varieties are more susceptible than others.
Conversely high temperatures at bud initiation can affect the outcome.
Try and determine their hardiness before purchasing!
Plants may be too small and in too much shade.
The soil may be of poor quality, and the pH may be wrong, 6.5 is considered a suitable level.
The soil may contain insufficient nutrients, or there has been excessive use of nitrogen fertilizer.
Any of these factors, may have allowed the plants to become too undernourished to support a large number of blooms, resulting in bud drop.
Some varieties flower earlier than others, meaning in some parts of the country a particular variety may grow well but in another it might not.
Checking on flowering period prior to purchasing may help.
Avoid growing varieties that bloom late in the spring.
Camellia bud mite may be a problem.
Spraying plants with an insecticide, applied as soon as flower buds have set, will usually control them.
Early flowering varieties are not as susceptible to mite attacks.
In conclusion: Basically anything that stresses a plant, can be a contributary factor to bud drop.