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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Sunchokes

Sunchokes, or Jerusalem artichokes (Helianthus tuberosus) are not so much a stable ground cover as masterful bed builders. They don’t just block, but obliterate grass lawn, taking the place of bed building mulch if handled correctly.

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Its home is the American prairie biomes, where it stretches for sun among massive grasses and other very competitive plants. Placing it in the standard lawn, full of short European grass species, or even an overgrown field is like releasing a saber tooth tiger into a playpen with modern house cats. It’s a brute.

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It begins by pumping nutrients from deep in the soil to power billowing clouds of leaves rambling up sometimes 15ft tall stems. At the end of the season, less fortunate species smothered below, it sucks all the nutrients gathered in its stems safely into the underground for storage in its edible tubers. Every year it sends out runners, some species more aggressive than others. One variety, “Supercluster,” Oikos Tree Crops sells is supposed to be well behaved, but most are decidedly imperialist, surging several feet out in all directions every year as resources allow. As long as it fills its nutrient reserves every year, the size of the open field it inhabits is its only limit.

To unleash the beast, get a bucket of the tubers in fall, and with a shovel, make little slits in the ground about one foot apart, inserting the tubers deep enough they aren’t exposed, and walk away. The days of the nearby plant residents are now numbered.

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Sunchoke sprouts
Don’t worry next spring when the tubers don’t sprout early. Sunchokes don’t like frost, and wait until late in the spring to pop up their furry little heads. I have planted these into completely unamended yards where lawn grass wasn’t even happy, but the ‘chokes still grew well. Results of removing grass and patch expansion are best if the patch is left a year or two before harnessing it for actual bed building.

It is very difficult to put strong beasts like sunchoke to use with brute force. You have to outsmart them. This you do by pinpointing their one weakness, and suddenly you have them in the palm of your hand. Because exploiting this weakness is so effective, I must go begging to my friends for new tubers in fall because I have accidentally wiped out my propagation patches.

I have quite a hard time removing their disbelief. Sunchokes are otherwise known in the gardening world as hard-to-chokes, which is why I don’t recommend digging up your newly cleared bed to remove the plants. I have never seen this work. Though you could swear all the tubers are removed, the plants always return. Some varieties were selected from patches sprayed with roundup -and lived.

Biologically, sunchokes are impenetrable tanks of ecosystem war, and have the potential to become the worst weeds for your new planting. I would not in any way suggest their use anywhere near your garden if it wasn’t for the one gap in their armor.

You see, ‘chokes go all out to ensure they get as tall and bushy as they can. Having invested every last bit of stored food from their tubers into the above ground stems, it’s as though the plant stood on top of the ground and could just be gathered up as a pile of stems to be placed somewhere else.

I discovered this one year when a particularly healthy, bushy specimen blew over in a windstorm, partially uprooting it. I broke the plant off, cracking up the lush growth to mulch the bed, expecting to see the plant return next spring. I was surprised when next year there was nothing.

Later, in a very dry year, sunchokes were the most lush thing in my food forest to feed my rabbit. She liked them, so I would snap off the growing tips, let the plants branch off to the side, and snap of the side branches to make rabbit happy. I started this when the plants were about 5ft tall, leaving about 4ft stems that in turn could return their nutrients to the tubers. Nevertheless the plants that normally topped ten foot came up the next year anemic, and dwarfed, barely reaching three feet.

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A young, thick patch of sunchokes.
The exact point in time when they seem most vulnerable is just before bloom at a certain time when the growth of leaves changes from being as tightly stacked and lush as possible, to becoming a bit more sparse, the stem getting harder, and the flower buds showing up quickly afterward.

Flowering, and in fact most dieback processes of plants, are accompanied by the production of ethylene gas, which in the ‘chokes I would guess also begin the back flow of sugars in the leaves to the more complex carbohydrates in the tubers, and oxidation of the stem fibers, making them woody and brittle. Cutting ‘choke down just before signs of this hormone’s activity seems to be their secret weakness.

In my climate, this means cutting the plants off about a foot tall in July. It is helpful to leave some stem to make lots of side shoots. A second cutting, about a month later, to remove the side shoots and what’s left of the stem, perhaps even some roots, in my experience, weakens the plant beyond recovery.

Some gardeners I have explained this method to ardently insist I’m wrong. They cite their own experience of mowing sunchoke patches for two years and the ‘chokes just growing up over and over again.

I have gotten excellent results with the method in my experience. That they were only a few years old unlike the decades old patches in these other reports may play a role. I doubt it though. On the one plant that blew over I saw a very large clump of tubers which I left in the ground.

Perhaps it is more a question of the plants adapting to growing less each time they are cut back, developing a sort of stunted homeostasis. They may have grown more miserly with their output of stored sugars. I think it is imperative that you allow the roots to put maximum growth above ground, then sap the last little bits of strength out of them with subsequent cutting.

Be cautious of course in planting the sun chokes and letting them run wild. If you closely follow the details I have given, I am confident you can get very similar results. Feel free to let me know how it goes.

Hacking off all this biomass leaves a lovely, thick mulch for planting into next spring. Grass is usually gone by this time. Adding some grass mulch early next spring ensures establishment is smooth the next year, but very little is necessary compared to normal bed building. If used well -in conjunction with the other ground covers, sunchokes are a real workhorse, with the potential to carry your efforts to the blissful state of an established, productive, ground thickly covered food forest.

Photo credits (because I’ve accidentally killed so many of my sunchokes with this method): Top photo by elzeva, second down Gurcharan Singh, third down Harald Biebel, bottom Tawee Wongdee

An inability to get fruit from wineberry

I like to explain my successes to my readers. But as you would guess there are some of what would currently be called failures in starting the food forest, some with no success in sight. 

A book I’ve been reading lately covers silent evidence -evidence that is never talked about because it is a failure or evidence buried under the sands of time and unknown. I mention this because perhaps such is the case for wineberry?

Wineberry (Rubus phoenicolasius) fruits on second year canes, this year being the third year my canes have been old enough to fruit but haven’t. The first two years late frost killed the second year canes (very frost sensitive), the later canes for that year coming up strong. 

A dead cane and a live one coming from the same root.
This year frost wasn’t to blame. Leaves grew, buds grew, and I was very excited to finally get fruit. In the heat of summer, after growing some very promising looking buds, they are shriveling up and dying without handing over a single druplet. The first year canes look fine.

The same cane with buds a few months earlier.

They’re even in the really happy guild where I have had success getting fruit from the apple (fruiting again this year) and turnip rooted chervil, among others. From what I’ve read about its culture, this site should be kind to it. It’s an invasive species here in several states, although not in my area (yet). I would prefer to not wait until it intoduces itself as a weed in my area to finally get some fruit.

There is an especially good article here about the wonderful production it maintains in shade. Flavor is supposed to be very good too. I have yet to come across information about it being finicky and never making a solitary fruit.

I have very few theories what the problem could be accept some strange disease which I have yet to find the name of.

I find the canes’ furry red spines rather attractive as a winter and spring interest, and the canes’ premature deaths make more mulch for the guild without my giving any attention to pruning. So why not keep them in hopes some year they will decide they’re ready to fruit? Until then, I thought I’d start the conversation about what seems to be a rare problem.

N-fix 5: Lespedeza

In the last N-fix I touched on the use of  autumn olives  (Eleagnus umbellata) in reclaiming strip mines. I wanted to continue this theme with autumn olive’s southern counterpart lespedeza.

Winter Lespedeza. Photo © Chris Evans, River to River CWMA, Bugwood.org
Winter Lespedeza. Photo © Chris Evans, River to River CWMA, Bugwood.org

Despite its similar occupation, Lespedeza bicolor is very different from autumn olive. It’s not actinorhizal, it’s a legume, the more common kind of N fixer. It’s hardly woody, it’s herbaceous, growing a full 6-12 ft every year only to die back to the roots in winter in my climate. Its root system is rather shallow, and quite fibrous. It’s a medium level nitrogen fixer, more in the range of amorpha. About the only characteristic it has in common with autumn olive is it grows like crazy in soil worthy of horror movies.

It’s been an invasive species that colonized and then poured out of the southern strip mines for decades. Lucky for us in the north, and probably the reason why I’ve never seen a lespedeza in any strip mines around here, lespedeza needs a long season to ripen its seed –a minimum of 160 frost free days.

You might wonder then how it has a range far in to Canada? There are exceptions. In fact the USDA selected for fast maturation of seeds in L. bicolor the most notable being ‘Natob’ which ripens seed a whole month earlier.

There’s an interest in the plant making seed because it was intended to feed wildlife such as quail. For this, and grazing animals the USDA mentioned switchgrass (Panicum virgatum) makes a good companion. Switchgrass grows very tall during hot weather so ditto for harvesting mulch.

So far I haven’t bothered with L. bicolor and have stuck to the more showy but similar L. thunbergii. My Neighbor has two cultivars, ‘Alba’ and ‘Gibralter’ in her yard, well over a decade old, and has never had them reseed or set seed on the ‘Gibralter’ as far as she can tell. Neither is a hybrid, but seed doesn’t seem to ripen for her.

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Lespedeza thunbergii ‘Alba’ in my neighbor’s garden. The gold in the background is a variety of black locust (Robinia pseudoacacia).
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My own little ‘Gibralter’ with the resident aster.

The two lespedeza in my food forest are side shoots from her ‘Gibralter’ I transplanted. Unfortunately they weren’t successful in growing to six foot like hers; they topped off and bloomed very prettily at three feet this year. I assume they’ll get that size once well-established.

I would like more though, because lespedeza’s drastic change in height every year allows for a lot of niche planting with tons of room available in spring, then partial shading in summer, and an all out eclipse in fall. Then too, the canes will last through most of the winter, creating a wind break for more tender plants.

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‘Gibralter’ nearly finished with flowering in my Neighbor’s yard.

The only possible problem could be the shallow root system. I haven’t experimented much with it, so can’t say how much it suppresses nearby plants, and my Neighbor mostly has other shrubs around hers. Best bet is probably spring bulbs such as camassia closest to it. Then a little further away where sun will last until at least mid summer you could plant Turkish rocket which is very taprooted and doesn’t do much after May. Good King Henry has about the same schedule but its roots don’t pierce quite as deep.

Two of our native species, L. capitata and cuneata are both much shorter, capitata topping off at four and cuneata at a two feet usually.  Cuneata is considered an invasive species in some states though, such that its sale has been banned in them. I don’t plan on growing them unless included in a pasture mix.

I prefer ‘Gibralter’ not only for its biomass, but its beauty. It has very deep pink color with an almost iridescent blue and purple hue on the tips if you look close. Often it’s placed near a pond in ornamental gardens to give the effect of a green and pink waterfall. Here is an excellent example

Overall, lespedeza is quite a diamond in the rough with whom I’m pleased to keep company.

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