N-fix 8: Albizia julibrissin

Terrible Tree #1 — Mimosa (Albizia julibrissin) What’s wrong with it: Weedy, short-lived, insect- and disease-prone, invasive roots, unattractive most of the year.

Comment: Yes, I know. You grew up with mimosas in the yard (sniff), they remind you of Meemaw’s garden (sniff, sniff), and they’re so pretty when their fluffy pink flowers open in early summer. But let’s get real. The flowers last about two weeks. Then they’re replaced by scads of these large, ugly, brown seed pods that hang there until the next spring. So for two weeks of beauty you get 50 weeks of gross. Plus, seedlings from your tree will sprout in everyone’s yard within a quarter-mile.

-Southern Living Magazine

Once the naysayers settle down to let me get a word in edgewise: Mimosa -specifically Albizia julibrissin or silk tree -in my climate at least, does not own up to any of these accusatory standards. To boost, it’s quite a proficient N-fixer.

As to their longevity: There are several specimen of silk tree in my area, many of which are over 30 years old, some, in really protected areas, nearly twenty feet tall, and only all the more gorgeous for it. Perhaps we are outside the range of its pests. On the other hand, winters around here often frost silk tree back to the ground. Such dieback actually extends their likely lifespan, because the wood is renewed. For plant cells, this is the equivalent of turning back the biological clock, and can be done over and over again.

Short lived flowers? Perhaps it’s the cooler weather, but the bloom lasts far more than two weeks around here. Some do only bloom for three or four weeks, but several I see start in late July, and continue without stop until October.

I should mention some trees of course have more color to their plume-like blossoms. The one below my neighbor found as a seedling even further north, from a parent tree whose flowers were this undesirable color. It came out alright I think.

As to “ugly,” “brown,” pods: They’re tan, if not gold. I find them very attractive. In fact, even less attractive pods like these on any plant are often highly sought by advanced garden designers for “winter interest” they provide. Of course, a barren landscape in winter is more a northern problem than a southern.

Seeding all over the place: In the south silk tree is considered a noxious weed, per its willingness to pop up everywhere. It’s doing its job of turning open space into riparian field, to become productive forest. Shame on you for hogging up petroleum, riding around a growling hog to keep open spaces it’s just trying to repair. But I’ll stop my rant there.

If this seeding were an issue in northern climates I would only be all the more delighted to grow this plant; but I can say from experience that we only find a seedling or two every year, quite close to the parent tree. These do not always survive to adulthood, and so are quite precious, usually given as gifts.

There are rumors of a few trees in this climate that seed especially well, but these are interestingly enough, ugly white-flowered specimens.

These considerations are for tall trees though. My neighbor has allowed her tree to reach the upper story of her forest garden between a magnolia,  Montmorency cherry, and serviceberry tree. For most food forests, silk tree has much more practical functions.

Soft design aside, the tree makes N. It grows footage of branches every year, which in our climate helps it bounce back from winter-kill. In the case of a food forest, this means lots of delicious mulch for healthy soil.

The USDA cites this plant as a medium level nitrogen fixer. One study noted it made far more nodules than other N-fixers, although only had medium level bacterial activity as pictured below. (Notice all the species aside from silk tree are decidedly tropical). View the full study here.

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This study in particular pointed out that nitrogen fixation is heavily dependent on sunlight for enough energy to run the nitrogen-fixing process. As a result, cloudy climates may not see such vigorous growth. But Ohio certainly isn’t the most sunny state; and many fast growing silk trees I have come across do so in half day’s shade.

I recommend taxing the tree of its growth for mulch at about time of bloom. You could just snap off the flowering branches with your bare hands. In the case that your tree has not reached blooming age but is getting out of reach for easily collecting mulch, just wait until about midsummer to begin snapping off branches.

One more practical accusation to address is the invasive roots. This refers to roots choking out plants below it, and roots becoming new plants. I should also mention that many accuse mimosa of allelopathy -manufacturing poisons for the surrounding plants (See Notes on Juglone for more info on allelopathy). Soil type, and climate can have major effects on how these attributes are expressed. I must report I find they don’t show up with the local specimen. My neighbor in particular has ferns, hosta, and tree peony below her mimosa. They have no complaint but for the slight dryness due to the thick branches above. Otherwise, they’re quite happy.

Studies have been conducted on mimosa and its relatives’ ability to inhibit germination in seeds. Although only a limited range have been placed in controlled studies, this study, for example, did not find any inhibition of germination.

View the rest of the text this image came from here.

The best way to propagate mimosa, aside from seeds which just need water, warmth and soil in most cases, is actually to dig up pieces of the root and let them sprout branches. I have tried cuttings, and they don’t root. If you are hacking up the ground with a shovel around the base of a silk tree, then perhaps you’ll get a sprout. We never have been lucky enough for this to happen around here.

When placing mimosa in design, I give it especially visible positions, where people can interact with it. For one client, I have mimosa at the corners of a grotto design where they will be allowed to grow as large as winters allow. The intent is to create a dome of arching branches. In winter these will quietly rustle with golden pods.

Placed where you might brush by the leaves, silk tree is especially entertaining, because it folds its leaves in response – a character which in plant terminology is called thigmonasty. The tree also folds its leaves at night, or in the dark before storms. This response to light is called photonasty. Below are some photos taken by my client of her young trees.

My client asked why the mimosa had stopped folding its leaves when she petted it. The fact is they can learn.  In The Hidden Life of Trees a study was cited which used dripping water as a means for stimulating a mimosa’s thigmonasty, causing it to shut. After many days of applying water in regular intervals, stopping, applying again, it learned this was not a threat, and got on with photosynthesis.

An intelligent tree like this is most desirable for adding to food forests as pleasure for the eye, delight for the curiosity, as fountains of mulch and fertility, for vibrant, healthy, cold climate jungles. Thank you for letting me state my position.

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Taste of chaos

Years ago, a hillside was tidied up. An apple tree growing there was pruned, grass around it ripped up. At the roots of the tree, clear plastic was laid; a layer of black plastic was laid over this, on top of this was laid colored woodchips

Alone, surrounded by short, browning grass in the heat of summer, its lower limbs sawed off, the apple tree died.

The owner changed. A new hand touched the wounds on this mortal tree, felt sorry, pulled back the layers of plastic, let the grass grow wild.


It was chaos. Briars and thorns grew up amidst the grass. Alongside these were fruit trees, vines, and shrubs.

Today I walked up the stone steps of this hillside, followed the meandering path that cuts through the long grass, and grasped one of many rusty-red peaches dripping from my trees.

Several of the peaches are fruiting abundantly this year. Because I have several kinds, some are ripe now, others a couple of months from now.


A fruit here, a fruit there has been the norm for years. This year there are just loads of fruit, beyond fresh eating, from goumi, gooseberry, saskatoon, currant. I often emerge from the food forest with fruits and berries for others to try.  Some look at the fruit, look at the food forest, look at me puzzled and ask: “Where did you get those?”

I have actually done the least in the food forest this year than any year before. I haven’t even mowed much of it. The rose bushes and blackberries I let grow up in the back of the food forest actually provided some fine mulch when I trimmed them back.


The amorpha and comfrey provided some very nice mulch also. I mainly mowed beside the road in order to mulch a new bed. Yet, as I walk around, plucking clusters of shining sweetness, I‘m quite pleased to see my beds are expanding themselves. Within the beds, several plants have achieved some of the most lush growth yet, with the turnip rooted chervil way above my head, and forming new patches in new beds.

To bite into the dewy sweetness of a fruit warm with sunlight here is unlike that of anywhere else. All fruit is a process. It is the workings of a place, coming to such a refined state as food. To bring in a fertilizer here, and bring in a spray there, is like making a patchwork of places and processes, in my mind. I much prefer fruits with vibrant flavor from comfrey mulch growing at the trees’ feet,  (comfrey mulch and tea does produce a notably rich flavor in garden vegetables too) and the spice of essential oils wafting around the air from such pest confusers as oregano or Spiraea.


I’ve had the privilege of working with chaos after letting it back into the garden. I think it’s got the idea of what I’m after. At this point in the food forest’s development, I am sure the chaos quite eagerly gets to work as I walk away from Mortal Tree, a fresh pit of a peach at its roots.

Ground cover infographic

Sunchokes is number ten in the Top 10 ground covers for food forests series I started a while ago. To help put everything into perspective, I made an infographic.

Scaled Infographic

The ground cover branch on the visual archive has links to all the original posts if you would like to find out more.

In general, the layout from right to left are ground covers that do well in established beds, to plants that simply wipe out other plants, and are excellent for bed building.

If you’re wondering how to share this on your own social media pages, try the share buttons below the post. I have most social platforms available for sharing.

I’m using the the term “dynamic mulch” to describe the ground covers, because ground cover has a rather flat connotation. Most gardeners think of them as useless plants that do nothing better than excessively clog the soil surface. They have much more potential.

I’m suggesting these plants as tools, not just for blocking weeds, but actively removing weeds, making use of otherwise useless plants through careful combinations, getting food from ground cover, improving the quality of the soil, and feeding other plants through their  well calculated use. With the correct use, resulting from a more dynamic comprehension of plants, we are suddenly on the brink of an entirely new level of sustainable, productive, passive agriculture and gardening.

The infographic, and the Top 10 series are part of a bigger surprise to which some of you closely following me have probably caught on. It should be ready before the end of the month. My apologies for making you wait, but I assure you, it will be worth it.

Update: It’s launched! Mastering the Growing Edge is live if you want to check it out.