The successful overwintering of the Chinese empress tree, especially during its youth, is a critical factor in its long-term survival and health in temperate climates. While mature specimens develop a considerable degree of hardiness, young trees are significantly more vulnerable to the challenges of winter, including freezing temperatures, frost cracking, and desiccating winds. Preparing the tree for its dormant period requires a proactive approach, involving specific cultural practices in the autumn and protective measures during the coldest months. Proper winter care ensures that the tree not only survives but emerges in the spring ready for another season of vigorous growth.
The tree’s natural preparation for winter begins in late summer and autumn as the days shorten and temperatures cool. It responds to these environmental cues by slowing its growth and beginning the process of dormancy. The newly grown stems and branches start to lignify, or become woody, which makes them more resistant to freezing. It is important for the gardener to work with this natural cycle. This means avoiding any practices that would encourage late-season growth, such as applying nitrogen-rich fertilizer or performing heavy pruning in the late summer or autumn, as this new, tender growth would be easily killed by the first hard frost.
One of the most important aspects of winter preparation is ensuring the tree is well-hydrated before the ground freezes. The soil should be kept adequately moist throughout the autumn, and it is beneficial to give the tree a deep, thorough watering after the leaves have dropped but before a hard freeze is expected. This ensures that the root system has access to sufficient moisture to sustain it through the winter. This is particularly important in windy locations, as even a dormant deciduous tree can lose moisture through its bark on dry, windy winter days, a process known as desiccation.
The degree of winter protection needed will largely depend on your specific climate zone and the age of the tree. In milder climates, a mature empress tree may require no special care at all. However, in regions where winter temperatures regularly fall well below freezing, or for any tree within its first two to three years of planting, implementing protective measures is a wise investment. These measures are primarily focused on insulating the vulnerable root zone and protecting the thin bark of the young trunk from damage.
Protecting young trees from frost
Young empress trees, with their thin bark and less-established root systems, are far more susceptible to winter injury than their mature counterparts. The primary goal during their first few winters is to protect both the roots and the trunk from the damaging effects of deep freezes and fluctuating temperatures. The most effective way to protect the root system is by applying a thick layer of organic mulch around the base of the tree in late autumn, after the first light frost but before the ground freezes solid.
This layer of mulch, which should be about 4 to 6 inches deep, acts as an insulating blanket over the soil. It helps to prevent the soil from freezing too deeply and protects the shallow roots from extreme cold. More importantly, it helps to moderate soil temperature fluctuations, preventing repeated freezing and thawing cycles that can heave the soil and damage tender roots. The mulch should be spread out to cover the entire root zone, which for a young tree extends at least to its dripline. However, be sure to pull the mulch back a few inches from the trunk itself to prevent moisture buildup which can lead to bark decay.
Protecting the trunk is also crucial for young trees. Sunscald is a common winter injury that occurs when the low-angled winter sun warms the bark on the south or southwest side of the trunk during a clear day. This warming can de-acclimate the bark tissue, and when the temperature plummets at night, this tissue freezes rapidly and dies, causing the bark to crack and peel. To prevent this, the trunk can be wrapped with a commercial, light-colored tree wrap or a plastic tree guard. This covering reflects the sunlight and keeps the bark at a more consistent temperature. The wrap should be applied in late autumn and removed promptly in the spring.
For very small saplings in particularly cold regions, creating a more substantial shelter can be beneficial. A simple structure can be built by driving three or four stakes into the ground around the tree and wrapping burlap around the stakes to create a screen. This screen will help to shield the young tree from harsh, desiccating winds and can also be loosely filled with straw or fallen leaves for additional insulation. This provides a protected microclimate that can significantly increase the chances of a vulnerable young tree surviving its first and most challenging winters.
Dormancy and seasonal changes
Dormancy is a natural and essential part of the empress tree’s annual life cycle. It is a period of rest, triggered by the shortening day length and decreasing temperatures of autumn, during which the tree’s metabolic activity slows down dramatically. The most visible sign of this process is the changing color and subsequent dropping of its leaves. By shedding its leaves, the tree conserves water and energy, as it no longer needs to support the large surface area of its foliage, which would be a liability in the cold, dry conditions of winter.
During dormancy, the tree is not dead but is in a state of suspended animation. Its energy reserves, produced through photosynthesis during the growing season, are stored in its roots and woody tissues. These reserves are vital for its survival through the winter and for fueling the initial burst of growth in the spring. A tree that has experienced a healthy, vigorous growing season and has been able to store ample energy will be much better equipped to handle the stresses of winter and to produce a strong flush of new growth when spring arrives.
The chilling requirement is an important aspect of dormancy for many temperate-zone plants, including the empress tree. The tree needs to be exposed to a certain number of hours of cold temperatures (typically between 0 and 7 degrees Celsius) during its dormant period before it is able to break dormancy and resume growth in the spring. This internal clock mechanism prevents the tree from being tricked into budding out during a brief warm spell in the middle of winter, which would result in the tender new growth being killed by subsequent cold weather.
As winter draws to a close and the days lengthen and temperatures begin to rise, the tree’s hormonal balance shifts, signaling the end of dormancy. The stored energy reserves are mobilized, and the sap begins to flow, carrying water and nutrients up to the buds. This marks the beginning of the new growth cycle, as the buds swell and eventually burst open, revealing the new leaves and flower clusters. The successful completion of the dormancy period is crucial for this powerful spring renewal.
Pruning and winter cleanup
The dormant season is the ideal time to perform most major pruning tasks on the Chinese empress tree. With the leaves gone, the tree’s branching structure is fully visible, making it much easier to identify and address any structural issues. Pruning in late winter, just before the new growth begins, allows the pruning wounds to begin healing quickly as soon as the tree becomes active in the spring, which minimizes the risk of disease infection.
The primary goals of winter pruning are to establish or maintain a strong structure, remove any problematic branches, and control the tree’s size. This is the time to remove any dead, damaged, or diseased wood that you may not have noticed during the growing season. You should also look for and remove any branches that are crossing or rubbing against each other, as these rubbing points can create wounds. For young trees, this is the time to focus on developing a single, strong central leader and a well-spaced framework of main branches.
For gardeners who are growing the empress tree for its giant leaves, a practice known as coppicing, late winter is the time for the annual hard prune. This involves cutting the tree down to a low stump, typically between 15 and 30 centimeters from the ground. This drastic pruning sacrifices the flowers for the season but stimulates the tree to produce a cluster of incredibly vigorous new shoots that will bear enormous, tropical-looking leaves. This is an excellent way to manage the tree in a smaller garden or as part of a mixed border.
In addition to pruning, a general winter cleanup around the base of the tree is a good horticultural practice. Raking up and disposing of any remaining fallen leaves and fruit capsules is important for sanitation. This debris can harbor the overwintering spores of fungal diseases, such as leaf spot, or the eggs of insect pests. By removing this material, you reduce the potential sources of infection and infestation for the following growing season, which is a key principle of integrated pest management and helps to keep the tree healthy in the long run.
