What is the overwintering temperature for grafted osmanthus on fringe tree rootstock?

The fringe tree (Chionanthus retusus), also known as April snow, is a relatively rare and precious protected tree species. In summer, its entire canopy is covered with white flowers, like a blanket of snow, clear and delightful. The fringe tree can not only be grown in pots, but can also be made into stump bonsai, and is moreover an excellent rootstock for grafting osmanthus. This is because the fringe tree has extremely strong adaptability to its growing environment, and also has a very long lifespan.

Bonsai makers mostly cultivate it as potted plants and then shape them into bonsai, especially for making osmanthus bonsai, for which it has extremely strong compatibility. In the Shandong region, people mostly use fringe tree grafting to propagate osmanthus, with excellent results. Using the fringe tree as a rootstock for grafting osmanthus is mainly achieved through approach grafting during the growing season, and should not be done during the rainy season or the dog days of summer.

Osmanthus, on the other hand, is a tree species that prefers sunlight, and also has the characteristics of being heat-tolerant and high-temperature-tolerant. Even in the hot summer, there is no need to take shade measures for it. Moreover, June to August in summer is the season when osmanthus flower buds form, and it needs to be provided with sufficient light every day. Even under high-temperature conditions of 30-35°C, it can normally complete bud formation, and the flowering rate is not low either.

But after all, osmanthus is not a cold-tolerant plant. After entering winter, especially in the harsh midwinter, in order to ensure it can overwinter smoothly, insulation and cold protection measures should be taken in time. So, at what temperature can grafted osmanthus on fringe tree rootstock safely overwinter in winter? Especially in the northern regions where temperatures are extremely low, how should we ensure the plant can safely overwinter?

Considering its poor cold tolerance, under normal circumstances it is necessary to ensure that the growing environment of the potted plant is not lower than 4°C, that is, the overwintering temperature for grafted osmanthus on fringe tree rootstock must be kept above 4°C. In order to enhance insulation and cold protection and ensure the plant can overwinter smoothly, in outdoor environments plastic film should be wrapped around the potted plant, which can also play a role in moisture retention.

Of course, if convenient, the potted plant can also be moved indoors for care to keep it warm and protect it from the cold, because if the plant suffers severe frost, it is very likely to cause leaf drop the following spring, and will affect normal flowering. Therefore, for potted osmanthus, winter insulation measures are indispensable.