The silk tree (Albizia julibrissin) has fern-like leaves and exotic-looking flowers. On each leaf, there are tiny leaflets that close when touched or as the sun sets. The stunning pink flowers that initially drew attention towards the silk tree inspire the origin of its common name. Each fragrant blossom is a silky pom-pom-like flower that starts with a white base and culminates with a shockingly pink tip.
While the tree is stunningly ornamental, it is also frustratingly weedy. It was introduced to the United States in 1745 by the famous botanist André Michaux. It is extraordinarily adaptable and does very well growing in disturbed soil and roadsides. Despite its invasive tendencies, the silk tree is beautiful and is very attractive to pollinators, including hummingbirds.
|Botanical Name||Albizia julibrissin|
|Common Name||Silk Tree, Pink Silk Tree, Persian Silk Tree|
|Mature Size||20-40 ft. tall, 20-50 ft. wide|
|Sun Exposure||Full, partial|
|Soil Type||Moist but well-drained|
|Soil pH||Acidic, neutral, alkaline|
|Hardiness Zones||6, 7, 8, 9|
|Native Area||Middle East, Asia|
|Toxicity||Seed pods may be toxic if ingested|
Silk Tree Care
A notorious spreader, the seeds of the A. julibrissin travel and grow in disturbed areas like roadsides, woodland edges, and open fields, so it can be difficult to control without careful measures. Other than the fact that it can get a bit untidy and needs to be planted a distance from structures due to weak wood that breaks easily under ice load and high winds, there is no simpler tree to grow once it gets going. The silk tree is a very hardy species tolerant of a wide range of soil and moisture conditions, bolstered by its roots’ ability to fix nitrogen.
The silk tree is certainly beautiful, but it has to be considered with some caution before planting. If in the Midwest or South, check if it is legal to plant. It is currently listed as invasive in various states. Individual localities may have it in “do not plant” ordinances in other locations. In addition to being invasive, the seeds may be toxic to pets and livestock.
The tree tolerates partial shade but is generally considered intolerant of shade. A. julibrissin will thrive in full sunlight, promoting fuller foliage and abundant flowering.
The silk tree tolerates a wide range of soil conditions and is even adapted to poor varieties. The tree’s nitrogen-fixing properties allow it to grow well in soils where other plants would suffer.
It can also handle acidic to moderately alkaline soil pH with ease and is a good choice for landscapes that need solutions for high alkaline areas.
The tree’s habit of naturalizing in wet to dry sites shows that A. julibrissin is adaptable regarding moisture conditions. Giving a young tree that is freshly planted a thorough weekly soaking is essential until the roots have been established. After the first season, no supplemental watering should be needed.
Temperature and Humidity
Though it thrives in the higher temperatures of the southern USDA Zones, the silk tree is tolerant of low temperatures. Young plants, however, are frost tender and will not survive hard winters.
The silk tree’s profuse growth shows that supplemental feeding is not needed. Compost added at the tree base should be sufficient to replenish nutrients.
Types of Silk Tree
There are numerous cultivars of the silk tree available.
- 'Ernest Wilson' is a winter-hardy option for northern zones. It has pink and white flowers.
- 'Rosea' offers bright pink blooms.
- 'Alba' has pristine white flowers.
- 'Summer chocolate' features unique, burgundy-color leaves.
Prune the tree in fall or winter during its dormant period. If you prune early in the tree's life, you can narrow it to a central trunk, though some prefer to allow it to have several smaller trunks. Regardless of that choice, it's best to prune the top of the tree to a flat shape, then prune back the branches to five or six buds on each. Remove dead, diseased, or weak limbs at any time during the year.
Propagating Silk Tree
Silk tree is easily propagated through seed or cuttings. To propagate through cuttings, choose a 6-inch healthy stem in late spring. Choose a branch that has not yet bloomed. Remove all but the top two or three leaves, dip the stem into water, and then into rooting hormone. Immediately place the cutting into a 4-inch pot that has been filled with high-quality potting soil. Place the pot in a plastic bag, then set it in an area of sunny yet indirect light, with a temperature of about 70 degrees Fahrenheit. Keep the soil moist. Expect roots to grow in three to four weeks.
How to Grow Silk Tree From Seed
Silk trees love to spread seeds, so harvesting them is not difficult. Collect seeds in the fall and store them in a cool, dry place until spring. For the best results, scrape the seed gently with a file or rasp until the hard outer coating is breached ever-so-slightly. Then place the seeds in an insulated container and pour hot, almost boiling water, over the seeds. Seal the container and allow them to sit in the hot water for 24 hours.
Dry the seeds and gently press them into the middle of a 3-inch pot filled with compost and perlite in equal amounts. Place the seed one inch deep. Place the pots outside, preferably against a shady, south-facing wall. Keep the compost mixture moist. Seeds can take anywhere from seven days to several months to germinate.
Potting and Repotting Silk Tree
When starting as seedlings, it's fine to keep the silk tree in its container until it begins to show roots through the drainage holes. At that point, it's time to transplant the tree to its permanent home in your landscape. When doing this, carefully place them in soil that has been amended with the same type of compost they began growing in.
This tree can tolerate temperatures down to about 25 degrees Fahrenheit but does much better in areas where the winters aren't as harsh. No matter the zone, make sure your silk tree is planted in full sun and in an area where it is protected from strong winter winds.
A variety of insects will feel quite at home in the silk tree, including soft-bodied creatures like mites. Mimosa webworms and cottony cushion scale are also attracted to this tree. Look into insecticidal treatments to help eliminate them.
Common Problems with Silk Tree
Silk tree is sometimes plagued by Mimosa wilt, a fungus that attacks the vascular system of the tree. Unfortunately, most trees with this problem die within a year, and it can spread to other plants in the vicinity. If your silk tree is infected, immediately remove it from the landscape.
How long does a silk tree live?
These trees typically live for ten to 20 years.
What are alternatives to the silk tree?
In areas where the silk tree is considered invasive, consider using redbug, flowering dogwood, sourwood, or fringe tree instead.
Can a silk tree grow indoors?
It is possible to grow a silk tree in a container. Choose a large container and fill it with loamy soil. Give the tree plenty of sun and keep it tightly pruned to remain compact. The 'Summer Chocolate' variety tends to be the best option for a container plant.