Mimosa is composed of lacy, fern-like leaves. It is a medium-sized tree and is planted as an ornamental due to its fall color show, puffy flowers and seed pods. The trees originate from China and are considered semi-tropical. Recommended growing zones are 6 to 9 and they are hardy to 0 degrees Fahrenheit. Severe cold and snowstorms can cause significant damage to the Mimosa tree.
The Mimosa tree that is grown ornamentally is often mistaken for another plant called mimosa, which is actually a sensitive plant. The ornamental tree is Albrizia Julibrissin and is in the legume family. The fern-like leaves are deciduous and measure 10 to 20 inches long. They are pinnate and composed of many small leaflets. The tree produces pom-pom-like scented flowers that give way to seed pods or fruits. The pods are 5 inches long, containing many hard seeds. The seed needs to be scarified before it will germinate. Mimosa can grow up to 30 feet.
Deciduous Plant Protection
The parts of a tree that sustain the most damage in a freeze are the leaves. Leaves are filled with water in each cell. When they freeze and thaw they burst, causing the leaf to die. This is why many trees native to cooler climes drop their leaves. The deciduous tree goes dormant in winter, which means that its stems turn liquid into concentrated sugar water to prevent freezing and subsequent damage.
When temperatures dip below 0 degrees Fahrenheit, especially for an extended time, an unsheltered Mimosa that has not lost its leaves will drop them within a short period of time. This can leave the plant susceptible to disease, since the leaves did not drop naturally and form scars to prevent pathological entry. The ends of the thinnest twigs and branches will blacken and die from the tip on up to 6 inches into the tree. The Mimosa can actually be killed down to the ground in severe weather, but it will probably sprout out of the ground again the following season.
In areas of severe cold, Mimosa should be kept in pots or very sheltered locations and moved indoors. In the case of plants left outdoors (but sheltered), you can get freeze-barrier fabric and cover the tree until the last frost passes. Any damage sustained on limbs and branches can be pruned out. The tree is quite vigorous and will most likely just bud and leaf on the remaining healthy tissue.
There are some new varieties of Mimosa that respond to freezing temperatures differently. The Chocolate Mimosa is quite sensitive to the cold and may not recover from freeze damage depending on the size and age of the tree. Larger trees of any variety are well established and have a better chance of recovery provided they were healthy to begin with. Mimosa 'Rosea' is hardy to one more zone and has been reported by growers to have a more vibrant and prettier flower.