When anyone asks me what's the best time to prune a mimosa, my instinctive response is, "Any time you can find a chainsaw."
That's very judgmental of me, I know, but heck, that's pretty much my job. And mimosa is one of those plants you either love or you hate. I hate it now. But I used to love it.
Why, when I was a kid, at the nadir of sensibility and good taste, I thought mimosa (Albizia julibrissin) was the prettiest tree in the world. Its leaves were like ferns. Its flowers were pink puffballs. And it bloomed in summer, when few other trees did.
A Miracle -- My Wife Agrees!
Judy, who notices very few plants, has fond childhood memories of mimosa too. She remembers climbing up in her neighbors trees to smell the flowers. I think they smell faintly of gardenias -- not like my son's socks, which would actually cause you to faint.
How It all Began
Native to the Middle East and Asia, mimosa was brought to this country in 1785 by the famous French botanist Andre Michaux, who planted it in his botanic garden in Charleston, South Carolina. It grew quickly into a vase-shaped, flat-topped tree, 30 to 40 feet tall, and it loved the Southern climate. The flowers, attractive to butterflies, hummingbirds, and colonial gardeners, ranged in color from nearly red to deep pink to flesh-pink to white. On one road-side near my home, there is a row of them, each a different color. Here's the usual pink.
And here's a white one. I really like the white, but I've never seen it for sale. The various colors are due to genetic variation, with pink being dominant. Where I live in Alabama, the trees usually start blooming in June and continue for several weeks into July.
So Why Do I Hate Mimosa Now?
Two reasons, First, like most all fast-growing trees, mimosa is notoriously short-lived, subject to many pests, and will die on you in a heartbeat. When people ask me the best way to get rid of a mimosa, I tell them to make it the focal point of their landscape and it will be gone momentarily.
Second, after the flowers fade, the tree grows hundreds of 6-inch long, bean-like, brown seedpods which hang from every branch. The seedpods persist all winter, even after the tree has dropped its leaves. Few trees look as ugly or more forlorn.
But wait! It gets worse! Each of those pods is filled with seeds and each and every one of them germinates somewhere, even in cracks in the pavement. Plant one mimosa in the yard and soon every house in the neighborhood has two or three mimosas. coming up in the fence, the middle of a bush, or by the silver propane tank.
Mimosa adapts to almost any well-drained soil, laughs at heat and drought, and does not mind if you spray-paint the trunk white, hang tires from the branches, or park your pickup on top of its roots. In hort class, we called it a "pioneer species," because if you disturb the land, remove native vegetation, and open the tree canopy to light, it's one of the first trees to appear. That's why you see it growing along just about every highway and country road in the South. Northerners be glad it doesn't like your cold winters, but with global warming, who knows how much longer you'll be free?
Not Fooling Me
Recently, a new kind of mimosa was introduced to the gardening world, a purplish-bronze leaf selection called 'Summer Chocolate.' The hype over its undeniably pretty foliage and pink flowers was overwhelming. Probably many of you bought one and are enjoying it right now. But not me.
See, any mimosa that flowers is going to produce seeds and lots of them. And if a thousand seedlings come up in my yard, I don't care if they have green leaves or purple leaves. They need to be eliminated with extreme prejudice.
So my advice about when to prune a mimosa remains the same -- whenever you can find a chainsaw.
Tell Me More About the Mimosa
Okay. Here’s a little crash course. The pink “powder puffs” of mimosa flowers appear in early June throughout the South. Fernlike leaves give the tree a lacy, graceful appearance.
A common problem are mimosa webworms. Silken webs wrap clusters of leaves together. The caterpillars inside those webs eat the leaves.
The solution: If possible, prune out and destroy webbing and damaged leaves. Thoroughly spray the tree trunk with horticultural oil in early March to suffocate pupating larvae. Rake and destroy leaf debris. Replace mulch under the tree each fall. Spray the tree with Bacillus thuringiensis kurstaki (Dipel, Thuricide, Javelin). For serious infestations, spray with carbaryl (Sevin), diazinon, or malathion.
Another problem you may encounter with mimosa is wilting. Leaves yellow and droop in early to midsummer. Many drop. Tree branches die over a period of several months.
The solution is that there is no control for the soilborne disease that enters through the tree roots. Discovered in the 1930s, it has now spread throughout the South. Remove infected trees. Do not plant new mimosas in the same spot.
Trees. Think About Trees.
No matter where you live or what garden style you prefer, the first questions you should ask when developing your garden’s design are, “Where are my existing trees?” and “What new trees would I like to add and where do I want them to go?”
As your garden’s largest living element, trees have an enormous impact, both practical and aesthetic. On the practical side, they offer shade and shelter from the wind, enhancing your comfort and often considerably reducing your home’s energy consumption. As design elements, trees can frame the house, establish scale, sport colorful blooms and foliage, conceal unsightly features, or draw the eye toward attractive vistas.
Among the most important contributions trees make to a garden is to lend an air permanence. While a hollyhock may give up the ghost after a year or two, an oak can live for centuries. A stately tree that forms the centerpiece of your garden may well have been the legacy of a farsighted gardener from many years earlier.
Choosing the Right Tree
When selecting trees for your garden, ask first what you want the tree to do. Should it shade the yard? Pick a tall-growing species that develops a sizable canopy. Should it hide a neighboring property? That may call for an evergreen tree with foliage all the way to the ground. Perhaps you’d like a focal point. Look for a tree with striking flowers, foliage, bark, or form. Once you have decided on the tree’s purpose, you can narrow your selection.
The most basic distinction between trees is whether they are deciduous or evergreen. Deciduous trees sprout new leaves in spring and carry them throughout the summer. In fall, the leaves may turn brilliant colors before dropping for the winter. Evergreen trees, on the other hand, retain their foliage year-round, making them ideal for screens or as points of interest during winter months. Broad-leafed evergreens, such as Southern magnolias and hollies, have wide leaves similar to many deciduous trees. Needle-leafed evergreens, such as pines and cedars, sport narrow, needlelike leaves.
Once you’ve decided between deciduous or evergreen, consider the tree’s growth rate and ultimate size. A desire for quick shade or instant privacy may tempt you to buy a fast-growing species such as silver maple or cottonwood, but such a vigorous tree can crack sidewalks, invade water lines, or quickly overwhelm the house, calling for replacement at a later date.
Consider, too, a tree’s mature shape (above)*referring to illustration*, which may not be obvious when you buy a small sapling at the nursery. A vase-shaped type, such as a Japanese zelkova, makes a good choice for a lawn or street tree, because its ascending branches leave plenty of headroom underneath. Rounded, spreading trees, such as live oaks and Norway maples, need lots of space to extend their branches. Columnar or conical trees, such as eastern red cedar and Arizona cypress, work well in closer quarters.
Many trees offer a spectacular burst of color in the fall, but consider their summer and winter foliage tones as well. Deciduous trees with golden, bronze, red, or bluish summer foliage should be treated as accents and used sparingly to avoid a jumble of colors. Likewise, use caution when selecting evergreens with colored foliage, such as many cedars and cypresses.
CARING FOR TREES (each section has an accompanying illustration)
Limbing up. Gradually removing a tree’s lower branches reveals the structure of the tree. This practice also increases the amount of sunlight reaching the ground, making it easier to grow grass and flowers around the tree. And it gives more headroom under the tree’s canopy. As a general rule, don’t limb up more than half of a tree’s height, less if possible.
Thinning. Selectively thin the branches of a shade tree to reduce the likelihood of wind damage, open up views, and prevent the tree from forming an overly dense canopy. Remove weak limbs and vertical water sprouts first, and any branches that rub or cross each other. Clear out branches growing toward the center of the tree. Then you can prune selectively along the main limbs, leaving a natural-looking, broad, and bushy top.
Preserving the roots. To keep a tree healthy, start at the bottom. If you build a patio or walkway around the base of a tree, avoid solid materials such as concrete, which prevent air and water from reaching the roots. Select paving that leaves as much open soil as possible around the trunk, use loose materials, or set bricks or paving stones in sand or gravel rather than cement.
If removing soil near a tree to construct a retaining wall or for some other purpose, try to preserve the existing grade around the tree by making any elevation changes beyond the branch spread. For soil-level changes over 2 feet deep, consult an arborist.
It seems obvious, but the easiest way to avoid disappointment with a tree is by selecting one well suited to your climate and soil. Don’t try to plant trees that are not reliably cold-hardy in your area or those that need more rainfall than you receive. Sooner or later Mother Nature will get even, and the trees will suffer from cold or drought stress, making them more susceptible to pests and diseases.
Other trees to avoid include those that are prone to pests; those with weak wood that can lose limbs in storms; those that drop messy fruit, seedlings (such as chinaberry above)*in picture*, or more leaves than you are willing to rake; and those with invasive roots. In addition to the trees listed at right *below*, your local nursery or garden center should be able to advise you on trees that are problematic in your region.
Ten Troublesome Trees
Think twice (or even thrice) about planting the following:
Arizona Ash (Fraxinus velutina)
Weak wood; invasive roots
Black Cherry (Prunus serotina)
Messy fruit; pest-prone
Box Elder (Acer negundo)
Lots of seedlings; pest-prone
Camphor Tree (Cinnamomum camphora)
Messy seeds; weak wood
Chinaberry (Melia azedarach)
Messy fruit; lots of seedlings
Eastern Cottonwood (Populus deltoides)
Weak wood; invasive roots
Hybrid Poplar (Populus)
Mimosa (Albizia julibrissin)
Pest-prone; lots of seedlings
Silver Maple (Acer saccharinum)
Weak wood; invasive roots
White Mulberry (Morus alba)
Messy Fruit; lots of seedlings
Why Not Top?
Topping — reducing the height of a mature tree by lopping off its top limbs — is the quickest way to ruin a tree forever. What’s more, it doesn’t even reduce the height of a tree for very long. Unlike a bushy hedge that soon sprouts new growth after being sheared severely, an older tree does not grow back in a natural-looking way when the trunk leaders or top branches are pruned to stubs. Instead, the tree sends out scores of weak shoots from the cutoff points; often these shoots are taller, coarser and denser than the natural top. Topped trees often develop heart rot, eventually resulting in hollow trunks. This makes them susceptible to storm damage.
Some topped trees might eventually regain their beauty, but the recovery can take decades. A good professional arborist will not top a tree, but will try other techniques to scale it back.