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IN WHICH A SMALL GAS MOLECULE HAS A BIG EFFECT

It’s a Gas

Ethylene is so simple. It’s a gas made up of merely two atoms of carbon and four atoms of hydrogen. Simple gases are generally not the kinds of molecules that make plant hormones which, like human hormones, are generally complex molecules with dramatic effects at extremely low concentrations. Nonetheless, ethylene is a plant hormone. I thought of ethylene as I sunk my teeth into the last garden-fresh peppers of the season a couple of weeks ago. Note that I wrote “fresh,” not “fresh-picked.” 

Those peppers were picked week or two before being eaten. I picked any green peppers showing the slightest hints of red, then spread them out on a tray. Many gardeners do this with tomatoes. I like peppers a lot more than tomatoes so only occasionally try to prolonging the season of fresh tomatoes.Peppers, ripening indoors

It’s ethylene that’s responsible for the transformations from unripe to ripe. Ethylene is produced naturally in ripening fruits, and its very presence — even at concentrations as low as 0.001 percent — stimulates, in turn, further ripening. The ethylene given off by ripe apples can be used to hurry along ripening of peppers or tomatoes, by placing an apple in a closed bag with them.
Ethylene structure
If the fruits are left too long in the bag, ethylene will stimulate ripening which will stimulate more ethylene which will stimulate even more ripening which will stimulate more ethylene which will stimulate still more ripening, ad infinitum, until what is left is a bag of mushy, rotten fruit. Apples can do this to each other, so one rotten apple really can spoil a whole barrel of them. 

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IT’S A GAS!

 Last Tomatoes & Peppers

   Late fall, and my thoughts turn naturally to . . . ethylene! You remember ethylene from high school chemistry. A simple hydrocarbon with 2 carbon atoms double-bonded together with 2 hydrogen atoms attached to each of the carbon’s remaining two free bonds. C2H4. It’s a gas, literally, and an important industrial chemical transmuted into such products as polyethylene trash bags, PVC plumbing pipes, and polystyrene packing “peanuts.”
    Oh, I forgot, this is supposed to be about plants. Ethylene is synthesized in plants and is a plant hormone with — as is characteristic of hormones — dramatic effects in small amounts.
    I think of ethylene as I sliced the last of the season’s fresh garden tomatoes for a sandwich a couple of weeks ago. Note that I wrote “fresh,” not “fresh-picked.” The tomatoes had been picked almost two months prior from vines I was cutting down and gathering up for composting. They sat on a tray in the kitchen, very gradually, over the weeks, morphing in color from light green to pale pink to deep red.

Tomatoes & peppers in November

Tomatoes & peppers in November

    Ethylene is responsible for this transformation from pale and insipid to red and flavorful (flavorful as compared with the pale green or pink stages, not as compared to vine-ripened summer tomatoes). It’s produced naturally in ripening fruits, and its very presence — even at concentrations as low as 0.001 percent — stimulates further ripening.
    The tomatoes shared the kitchen tray with peppers, peppers that also were green when laid on the tray. All ripening fruits produce ethylene, peppers included. So let a green pepper sit long enough and — as long as it is sufficiently mature and does not dry out too much, or rot — it will ripen red, or yellow or purple, whatever is its ripe color. Which mine did.

Yes, One Rotten Apple Does . . .

    The ethylene given off by a ripe apple or banana can be put to use in speeding up ripening of tomatoes. Just put either of these fruits into the bag with tomatoes. Apples and bananas are climacteric fruits which, instead of emanating a steady stream of ethylene, ramp up production dramatically as full ripeness nears.
    Among other effects, ethylene production itself stimulates further ethylene production. So if ripening fruits are left too long in a bag, ethylene stimulates ripening which stimulates more ethylene which stimulates more ripening, ad infinitum, until what is left is a bag of mushy, overripe fruit. Hence, one rotten apple really can spoil the whole barrel.

It’s a Gas for Fruiting Also

    Ripening isn’t the only prod to ethylene production in a plant. Stress also can do it, whether from the nibble of an insect, a disease spore wending its way through a plant’s cuticle, wind or snow bending a branch, or pruning shears trimming a wayward branch.
    Exogeneous ethylene leaves its mark on more than just promoting ripening. A century and a half ago, pineapple growers in the Azores saw that plants nearer outdoor fires flowered soonest. Plants that flower sooner, fruit sooner.
    If you’ve rooted a pineapple crown — relatively easy, just twist it off, plant in pot of well-drained potting soil, and water only when soil dries out — you can speed flowering and fruiting by setting an apple in the crown for a few days, then covering the plant with a bag.

And for Not Staking (Too Much)

    Soon, I’ll be going outside, pruning shears in hand, to put ethylene to use again. Ethylene also slows growth, in so doing coaxing flowering.
 

Flowers on bent pear branch

Flowers on bent pear branch

   Pear trees are famous for being slow to settle down to flowering and bearing fruit. No, I’m not planning to hang apples in the pear trees and enclose them in plastic bags! I am planning, after I finish working on the trees with my shears, to bend some well-placed branches to a near horizontal position, using weights, string, and pieces of wire to hold bent branches in place. The stress of bending — compression on one side of a stem, expansion on the opposite side — steps up ethylene production (30-300%), slowing growth, inducing flower bud formation, and shortening the time till I bite into my first pears from young trees.
Young tree, staked    I’m not yet finished with you ethylene. I planted a few new apple trees this year. They need staking, but not too much. Stakes should allow some movement of the developing trunks, and free movement of the top third of the plants. Movement causes the same stresses as branch bending, likewise inducing ethylene production. Ethylene, as you now know, slows growth but also, as you might not know, increases the thickness of the moving part; i.e. makes for a sturdier trunk. That’s what I want for my young trees.

SUNNY DAYS & YOGA, BUT TOMATOES?

Springtown Farmden Health Spa

    In the past, I have written of rei-king and sie-thing as two of the many healthful exercises offered here at Springtown Farmden Health Spa. We now have a new offering at the spa: garden yoga or, more catchy, gardoga or yōgdening. I like the last one best.
    Yōgdening grew out of my respect for the soil, my desire to maintain and foster a healthy balance of life below ground. A healthy population of bacteria, fungi, worms, actinomycetes and other below-ground dwellers translates to healthy plants above ground. Those beneficial creatures need to breathe, which is why most gardeners and farmers till their soil. To aerate it.

Yogdening, for health and weedlessness

Yogdening, for health and weedlessness

    But tilling a soil also burns up valuable organic matter. This organic matter feeds soil organisms and, in turn, plants, makes nutrients already in the ground more accessible to plants, helps hold moisture for plants, and helps aerate the soil.
    I avoid the need to till my soil for aeration by almost never walking, rolling a wheel barrow, or allowing any other traffic where plants are growing. Plants in fields and forest grow well despite never being tilled except what earthworms and other small animals manage to do. (No small amount: Charles Darwin computed that earthworms completely turn over the upper six inches of a pasture soil every 10 to 20 years — in England, at least.)
    Getting back to yōgdening . . . Weeds are making inroads into certain parts of my gardens. Not my vegetable gardens, the 3-foot-wide plant beds of which I keep well weeded with my feet firmly planted in the 18-inch-wide paths bordering the beds. But the only way I can reach into some other planted areas, a bed of various flowers sprawling beneath some Asian pear espaliers, for example, is by stepping into them. To minimize foot traffic, after stepping into a planted area, I try to keep my foot anchored in place, from which I pull every weed I can reach.
    As you might imagine, reaching every weed possible with feet planted in one place calls for all sorts of contortions and stretches forwards, backwards, and sideways involving my legs, trunk, shoulders, arms, and neck. My guess is that after a half-hour of weeding, I’ve run through a close approximation of Utthia Trikonāsana (Triangle Pose), Vīrabhadrāsana (Warrior Pose), and Uttānāsana (Standing Forward Fold Pose), to name a few classic yoga poses — and cleared away weeds!
    Weeding (or, perhaps, I should write “we-ding,” another spa offering) is especially satisfying this time of year. Dry weather has slowed sprouting of new weeds so cleared areas remain clear.

Brown Rot Not (Too Much)

    Dry weather is also good for fruit ripening. That is, ripening rather than rotting. As sweetness develops in ripening fruits, they become more susceptible to rotting. Fungi, like humans, can make quicker use of simple sugars than more complex carbohydrates, such as a are found in unripe fruits. Fruits with thin skins are especially susceptible to attack from fungi.
    For a variety of reasons, known and unknown, this has been a good year for plums. In past years, late frosts in spring have snuffed out blossoms or plum curculio has caused many, if not all, plumlets to rain to the ground. This year, blossom buds were unscathed from winter cold or spring frosts, curculios were kept at bay by my spraying Surround, a commercial product that is nothing more than kaolin clay.
 

Shiro plum

Shiro plum

   Current dry weather should also limit plums’ other nemesis: brown rot, a fungal disease that turns ripening fruit gray and fuzzy and then, at the end of the season, into dark brown, shriveled mummies. (Of course, beautiful clear days are often followed by clear nights during which water, in the form of dew, condenses on fruits and leaves.) The mummies hang from the branches, along with cankers on branches, spread spores and infection the following year. Fallen mummies are also a source of the following season’s infection.
    Brown rot gets to work early in the season, around blossom time, and then later in the season, as fruits are ripening, which is now, for my Shiro plums. Early in the season, I added sulfur, a naturally mined mineral whose use as a fungicide goes back to the ancient Greeks, to the mix when I was spraying Surround.
    Supplementing that spraying was cleaning up hanging and fallen mummies at the end of the season, and promoting drying of branches and fruits with pruning and thinning out of excess fruits.
    The upshot is that some brown rot is showing up on ripening plums. But not all of them. And those that have been spared are delectable. Even the birds think so. Their peckings, unfortunately, like wounds inflicted by plum curculios, increase fruits’ susceptibility to brown rot.

Tomatoes, Where Are You?

    Tomatoes are growing like gangbusters, here and in other gardens I’ve seen locally. And the fruits are likewise growing very plump.
 Tomatoes, not yet ripe   But the scene is not as rosy as it should be, literally, because too many of the tomatoes are still green. Again, other local gardens mimic my experience. How are your tomatoes doing this year?
    Day after day of bright sunny, weather and moderate temperatures should have promoted ripening. Then again, day after day of rainy weather last month might have retarded it. At any rate, in gardening and farming, you can’t go wrong blaming the weather.
   

Who’s the Best Gardener/Farmdener?

Fresh Watermelon, and More, with Help from Ethylene

Could I possibly be the best gardener west of the Hudson River? Perhaps. As evidence: On November 1st, here in Zone 5 of New York’s Hudson River Valley, where temperatures already have plummeted more than once to 25°F, I was able to harvest a fresh, dead-ripe watermelon. Not from a greenhouse, not from a hoop house, not even from a plastic covered tunnel. Watermelon, a crop sensitive to frost and thriving best in summer’s sun and searing heat.

Okay, perhaps I can’t assume all that much responsibility for the melon. Let me explain . . . 

Every fall, I have a landscaper dump a whole truckload of leaves vacuumed up from various properties at my holding area for such things. Rain and snow drench the pile in the coming months, starting it on the road to decomposition. When sufficiently warm weather has decided to stay in spring, I scoop out a few holes in the pile, fill them with compost, then tuck in watermelon transplants.

Last fall’s pile yielded well from summer until early fall this year, at which time I gathered up remaining melons for eating or, if unripe, for composting along with the vines. The tractor, with its bucket, was able to move and compact the now dense pile to make way for this  year’s crop of leaves.

 

Ben & Jeremy show off the November watermelon.

Ben & Jeremy show off the November watermelon.

Now we’re up to November 1st, time to spread the leaf mold before it freezes — a big job that necessitated enlisting the help of my neighbors Jeremy and Ben. We were loading and hauling and loading and hauling, forking deeper and deeper into the bowels of the pile, when Jeremy yelled that he’d just speared a watermelon I had overlooked when cleaning up. I cleaned it off and sliced it open. It proved to be a ripe watermelon. The taste? “Awesome,” to quote Jeremy.

The Watermelon Mystery

Okay, I admit to not being able to claim too much credit for the ripe watermelon. How did it get there? Was it ripe and overlooked, then buried and preserved in the warm bowels of the leaf mold pile? Was it unripe when buried, then subsequently ripened? Probably not. No leaves were poking out of the pile, capturing the sun’s albeit weak rays for photosynthesis to make the sugars needed for ripening. A couple of nights of 25°F would have done in the leaves anyway.

Some fruits can actually ripen after harvest. These include apples, pears, bananas, avocados, and other so-called climacteric fruits. Just before ripening, respiration of climacteric fruits dramatically increases along with a burst in production of the plant hormone ethylene. Through a feedback mechanism, ethylene stimulates more respiration which in turn stimulates even more ethylene production and even quicker ripening. Hence, enclosing bananas in a bag stimulates ripening, and why one rotten apple — injury, whether mechanical or from pests, also elicits an ethylene response — can indeed “spoil the barrel.”

This burst in ethylene production occurs even after climacteric fruits have been harvested, as long as they were sufficiently mature at the time. You can’t pick a golfball-sized green apple and expect it to ripen off the plant.

Non-climacteric fruits lack that pre-ripening spike in respiration and ethylene production, and do not ripen after harvest. Or so the thinking, based on early experiments, went. According to more recent research, fruits show various degrees of ethylene production. Watermelon is not a climacteric fruit, but at a certain point the white flesh within does release a burst of ethylene some time after which it morphs from bland and unripe to sweet, red, and ripe. But that won’t happen off the vine.

(“Ripe” is open to some debate. Peach, for instance, is a climacteric fruit that, if picked sufficiently mature but underripe, will soften and become more edible. But it won’t develop the aromatics of a tree-ripened fruit or, until rotting changes starches to sugars, become at all sweeter after picking. I don’t call that “ripe.”)

So my watermelon must have been overlooked and ripe and evidently kept perfectly well in the moist warmth of the leaf pile.

Deb & Ethylene Take Credit for the Peppers

Ethylene, and not me, is going to take credit for the fresh, sweet red peppers in today’s salad. Peppers are a climacteric fruit. Green peppers are unripe peppers, but if the fruits have just a hint of red on them, they can ripen even after harvest to full red (or yellow, orange, or purple, depending on the variety of pepper) color and, at least to my taste buds, flavor.

Still eating fresh, red, ripe sweet, juicy, delicious peppers.

Still eating fresh, red, ripe sweet, juicy, delicious peppers.

Skill is needed to ripen peppers off the plant. Cool, but not too cool, temperatures hold the fruits for storage and warmer temperatures then speed ripening. Just the right amount of humidity is also needed to, on the one hand, avoid drying, or, on the other hand, rotting. My wife, Deb, rather than I, plies these skills, so should probably get credit for the ripe, red peppers.

This season has been the best pepper season ever, both in quantity and in quality. King of the North peppers, large and blocky, with thick, juicy walls, now ripening in a basket taste as bland now as they did all summer. I won’t grow them again. In contrast, Carmen, Sweet Italia, and (slightly hot) Pepperocini peppers, also ripening in that basket, taste as good now as their siblings did snapped from plants basking in summer heat and sun a few months ago.