Mimosa or silk trees, as they are commonly known, are fast-growing deciduous trees that reach up to 30 feet in height at maturity. They are known for their fluffy white to pink flowers that bloom from late spring through summer and resemble a bottle-brush head or fiber-optic threads. They also produce heavy litter from the flowers and seed pods. Short natural lifespan, pests, cold temperatures, poor cultivation practices or the application of herbicides can all play a role in killing mimosa trees. Signs of death are found in the pattern of growth, flowering, seed development, branch and trunk wood health and in the coloration and vigor of foliage.
Monitor the tree for signs of fusarium wilt, an incurable fungus that can discolor the leaves, causing them to wilt and either attach to the branches or drop to the ground. Look for brown stripes and discoloration in the wood just under the bark layer as another indicator of infection. A wilt-infected tree may fail to produce flowers and seeds and the branches will die back on just a portion or over the entire tree. New shoots may appear from the ground after die-back from wilt, but they will remain infected.
Observe the growth rate of your mimosa. They typically grow quickly, producing 3 feet of new growth each year up to a maximum height of 30 feet. If your mimosa is well under the mature size of 20 to 30 feet in height but does not grow in size over a season or two when provided with consistent cultivation practices, it is likely dying.
Determine the age of your mimosa tree, as the species has a relatively short lifespan, generally fixed at 10 to 20 years. If your mimosa is in this age range and is exhibiting branch death, failure to bloom and defoliation during the peak summer growing season, the tree may be past its viability.
Determine you climate zone, especially if your mimosa tree is growing in a climate colder than its natural range (between USDA Zones 6 and 11). When planted in colder zones, mimosas can die back to the ground and produce smaller sucker growth in the spring. If it has died back and no small branch sucker growth develops over the course of a year, the tree has likely succumbed to the cold temperatures.