In the tropics, "mimosa" bonsai is the common name for bonsai created from the Leucaena leucocephala (aka L. glauca).
The temperate tree, Albizia julibrissin, is also called mimosa but they are very different.
This page is about the tropical mimosa. In the wild, this tree usually grows fast and straight, has very little taper, the leaves and seed pods are large.
Some common names for Leucaena are Lead Tree, White Leadtree and even Weed Tree. There are over 24 species of Leucaena but the L. glauca (syn. leucocephala) is the one best suited for bonsai. It can be found growing wild throughout Florida, Texas, and the Caribbean as well as much of Central and South America. It's also available in Hawaii.
Although considered an “invasive exotic” in Florida - Honduras, Mexico and many Central American countries value some species of Leucaena as a tree for “livestock feed, reforestation, soil regeneration and fuel wood”.
What else is it good for? Bonsai!
These two mimosa bonsai were grown from seed. Originally they were two separate shohin bonsai. Placing them together had a pleasing result.
If you’ve never tried a bonsai from seed, tropical mimosa may be the perfect choice. Unlike pine trees, the response and results are rapid.
Seeds are best started in spring when they ripen on wild trees. Green pods are not ready yet. When pods turn brown they often ‘pop’ open on their own. Pick them when they are just right, open the pod to find the many small seeds. Plant the dry seeds in nursery pots containing soil with some organic content … don’t use soil-less mix for this project. Plant the seeds about ¼ inch deep. Keep them moist but not soaking wet.
Germination takes 2-3 weeks in Florida. It may take longer in other areas. More than half of your seeds should germinate.
Foliage can be pruned any time of year. Defoliate frequently.
Any time a leaf becomes too large, remove it. (This may happen several times a year - at no particular time.) Eventually small leaves will develop and be easier to maintain.
Frequent defoliation and pruning does not seem to damage the tree in any way. Let them grow a little wild in winter, then root prune and cut back hard in early spring.
Tropical mimosa bonsai roots can fill up a container quickly.
You may need to water this plant more frequently than some of your other bonsai. Root prune at least once a year, twice if necessary. Repot spring through summer in most areas. (In the tropics you can repot any time of year.)
You can safely remove half of the roots (or more) by cutting them with shears. It’s best not to rake roots as they break easily.
This is truly a hard-to-kill plant.
This photo shows what happened when a small potted mimosa was ignored in the nursery for a year.
Not many people are working with larger specimens of this plant. (Mainly because it is difficult to find them with nice shapes.)
This curved trunk, collected specimen was on display in Hawaii with flowers and seeds. The owner said he purposely let the seeds and flowers grow out especially for the exhibit. He wanted people to know they do bloom.
When grown from seed Leucaena can make a good bonsai (especially shohin and consider bonsai mame also.)
They are quick to develop and the aged look to the trunk appears early on. To start, let the plant grow long and tall to develop thickness of trunk, then cut it way back.
This is one of the most durable plants to cut severely. In a very brief time new branches will develop. Although they will grow just about anywhere, you will have best results with leaf reduction when grown in full sun or at least very high light. It prefers to be evenly moist.
This mimosa doesn’t need much encouragement to grow. Do not use high nitrogen fertilizer to push new growth (Nitrogen is the first number of three, listed on package). It will encourage leggy growth.
Because tropical mimosa needs so much pruning, this plant rarely develops flowers as bonsai. When it does produce flowers, they are a creamy white inflorescence. Except for the color, they are very similar to the dwarf powder puff.
They (also like the Calliandra) are great bee attractors.
Remember, this is a tropical plant and will not tolerate frosts and freezes.
Ben Liss, Ft. Lauderdale FL, purchased his first mimosa bonsai at a Miami bonsai club auction. It was old looking but needed some work.
The amazing mimosa metamorphosis by air layering article has great picture details.