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IN WHICH A SMALL GAS MOLECULE HAS A BIG EFFECT

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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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ABOUT PEPPERS

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Better Late than Never

Cold has finally gotten the better of my pepper plants. Two below freezing nights a month ago started their demise, and two more during the last few nights finally finished them off for the season. Not the fruits, though, plenty of which are piled and spread out in trays and baskets in the kitchen.
Peppers in various stages of ripening
Outdoors, fruits weathered the below freezing temperatures well. They’ve been shielded from the full brunt of cold by their canopies of increasingly floppy leaves. Also, fruits of plants are higher in sugars than are the leaves. Thinking back to high school chemistry, I recall that any solute, such as sugar, lowers the freezing point of the solution. So pepper fruit cells can tolerate more cold than pepper leaves.

Even with the plants dead outside, the pepper season isn’t over here. The season has been greatly extended by harvesting and bringing indoors sound, green peppers showing any bit of red — or yellow if that’s the pepper’s ripe color. Sitting in trays and baskets in the kitchen, these mostly green peppers have been ripening, depending on when they were harvested and how long they’ve sat, to fully red or yellow color, when they are most flavorful (to me).
Peppers in trays and baskets
For some reason, perhaps the heat interfering with pollination, peppers started ripening later in the season than usual. The present and the past few week’s abundance of them makes up for the late start.

Thank You C2H4

For the peppers’ morphing from green to red or yellow, I have to thank, in large part, a simple gas made up of just two atoms of carbon and four atoms of hydrogen. It’s ethylene, a plant hormone. Most plant and animal hormones are much more complex molecules.
Ethylene diagram
Ethylene is produced naturally in ripening fruits, and its very presence — even at concentrations as low as 0.001 percent — stimulates further ripening. The ethylene given off by ripe apples can be used to hurry along ripening of tomatoes, by placing an apple in a closed bag with the tomatoes.

Banana, apple, tomato, and avocado are among so-called climacteric fruits, which undergo a burst of respiration and ethylene production as ripening begins. These fruits, if picked sufficiently mature, can ripen following harvest.

Peppers, along with “figs, strawberries, and raspberries are examples of non- climacteric fruits, whose ripening proceeds more calmly. Non-climacteric fruits will not ripen after they’ve been harvested. They might soften and sweeten as complex carbohydrates break down into simple sugars, but such changes might be more indicative of incipient rot rather than ripening or flavor enhancement.” Or so they say. And, I admit, I’ve said; that quote is from my book The Ever Curious Gardener. (The rest of the section about ethylene in my book is correct.) They and I were wrong.

So, I’ve learned two things. First of all, pepper do ripen well after harvest, not only to a bright color but also to a delicious flavor. And second, further reading has revealed that hot peppers, but not sweet peppers, are, in fact, climacteric fruits.

What about semi-hot peppers? Or non-hot hot peppers? (Read on.)

Hot and Not

I did also grow some semi-hot peppers this season. Roulette is a variety billed as resembling “a traditional habanero pepper in every way (fruit shape, size and color, and plant type) with one exception – No Heat!” Roulette had an interesting flavor that I both liked and didn’t like (mostly liked), and occasional ones did have some heat to them, but that might have been due to their proximity to . . . 

Red Ember is billed as an early ripening hot pepper with “just enough pungency for interest.” It definitely caught my attention when I bit into one! Call me a wimp, but I thought it was fiery hot.

Peppers, Red Ember and Roulette

Peppers, Red Ember and Roulette

In my previously mentioned book, The Ever Curious Gardener, I also explored flavor in fruits and vegetables and, briefly, hotness in hot peppers. “Studies have been done with peppers, focusing specifically on their hotness, which, to muddy the waters, stems from not one, but from a whole group of compounds, capsaicinoids, mostly capsaicin and dihydrocapsain. Hotness in peppers was found to depend on the variety, the environment, and the interaction between variety and environment, with smaller fruited peppers less influenced by vagaries of the environment. Usually, but not always, a pepper will have more bite if plants are grown with warmer nights, with colder days, with just a little too much or too little water, or with fertility imbalances; increased elevation elicits the fiercest bite. Basically, with any sort of stress.”

Uncommonly hot temperatures this summer may very well have turned up the heat in Red Ember and put some heat in Roulette.

MYSTERY OF THE UNDEAD ROSE

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 Death shows Life

   It was with red rose in hand — a long-stemmed red rose — that Deb returned from a recent bridal shower. The rose was a party favor, the flower a welcome sight in the dead of winter. It found a home in a vase of water on the kitchen table.
    After a week, the rose was still sitting on the kitchen table, its bloom looking as perky as the day it had arrived. After two weeks, still no change.
    Okay, I’m sure that the vase was clean, the water fresh and initially warm (for quicker absorption into the stem), and that the base of the stem was freshly cut at a 45 degree angle just before immersion. All that, and the cool room, would make the blossom last longer. But that long?

Commercial rose, after 2 weeks

Commercial rose, after 2 weeks

    No special potions were added to the water. Like sugar, to feed the leafless stem and flower. Or an acidifier to make the water’s acidity more near that of the cell sap, stabilizing the flower’s color. Or an inhibitor to prevent microbes from running amuck. Such potions can be purchased or made at home by mixing: 1 teaspoon of sugar, 1 teaspoon of plain household bleach, 2 teaspoons of lemon or lime juice and a quart of lukewarm water; or mixing 2 parts water to 1 part tonic water (or non-diet lemon lime soda).
    The problem was that the blossom was eerily too alive after a couple weeks. Without roots, sunshine, or leaves, the flower should have started dropping petals and looking generally forlorn. It didn’t, at least not quickly enough to exude that there was a life force within.
    Contrast this behavior with that of the carnations (Dianthus caryophyllus) that blossom sporadically in my greenhouse through winter.  I cut the fragrant, pink blossoms, put them in a vase of water, and within a week they’re spent.
    I’ve gained appreciation for the transience of cut blossoms. Their timely decline and death declare their aliveness.

Blame it on (a) Gas

    Comparing roses and carnations may be like comparing apples and oranges.
    Ethylene, a simple gas that’s also a potent plant hormone, comes into play here for its role in plant senescence, including that of cut flowers. Combustion, whether from a cigarette, an automobile engine, or a candle, produces some ethylene, as do plants themselves, especially when they are wounded or in their final throes of aging.
 Carnation, fragrant and pretty   Carnations are among flowers, along with baby’s-breath, lilies, snapdragons, and most orchids, whose ethylene production ramps up as senescence begins. These flowers also are very sensitive to the effects of ethylene, which speeds aging, which generates more ethylene, which further speeds aging, which . . .
    Roses, in contrast, are less sensitive to ethylene. (And ethylene plays no role in the decline of daisies, daffodils, and irises.) Also, as a commercial product, the long-stemmed, red rose that sat on my kitchen table could have been pre-treated with silver thiosulfate or aminoethoxyvinylglycine, both ethylene inhibitors.
    No matter. I don’t require a whole lot of carnation blossoms, and new ones appear at a rate sufficient to replace spent ones, or, if slower, to increase appreciation for each new one.

In the Greenhouse, Out with the Old, In with the New

    All winter, the greenhouse beds have been vibrant green with lettuce, arugula, celery, parsley, mâche, chard, kale, and claytonia. Just lately, the greenery has lost some of its vibrance.Lettuce going to seed
    Planted in early fall, these greens grew to size — as hoped — to provide good eating through winter. Over the past few weeks, as days grew short and dim, and temperatures cooled, the greenery — as expected — mostly just sat still. In anticipation, I had grown them to size before the onset of winter. A bigger greenhouse would allow for a little something to be harvested from a lot of little, slow growing plants, enough for the daily fare. But the greenhouse is what it is.
    And some of the lettuce plants, though not very big or old, are going to seed. It seems that lettuce transplants, rather than plants from seeds planted right in the ground, are more prone to this bolting.
    Time for some fresh young growth: I pulled out some old and bolting plants, and sowed fresh lettuce, spinach, and arugula seeds. Growth will be slow for now; older plants should supply sufficient harvest until young’uns are ready for picking.

IT’S A GAS!

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 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.

Who’s the Best Gardener/Farmdener?

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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.

Oiling a fig

OILING MY EYES

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I’ve always wanted to oil the eye of a fig, and finally got around to it a couple of weeks ago. Not that oiling a fig’s eye is something new or something that I came up with; fig lovers have been oiling their eyes at least since 300 B.C.E. And our reason for doing it is to speed ripening.
My oiled fig is the variety Kadota, which grows in a pot sitting in a sunny, south-facing window. Still, the amount of light streaming through those panes this time of year is around 500 foot-candles, as compared with a 10,000 foot-candle bath from summer sunlight, which figs do love. Light intensity and duration dropping daily justified a little oiling to speed up ripening. All that’s required is a drop of oil placed on the eye — the ostiole — of the fruit. Because olives and figs share Mediterranean origins, olive oil seemed most appropriate for fig-oiling.
Although fig-oiling has been practiced for centuries, it’s not some peasant tradition without scientific underpinnings. In fact, oiling releases ethylene; this simple hydrocarbon, comprised merely of two carbon and 4 hydrogen atoms, also happens to be a plant hormone. Present at the right time at the right concentration, ethylene stimulates ripening of fruit.
Not that I had to use olive oil. Other vegetable oils also speed ripening. The more refined they are, the greater the effect. 

You can’t oil just any old fig fruit and expect it to ripen. The fruit must be near enough to the time of natural ripening. The two fruit that I oiled were among the four that were large enough to be deemed by me to be ripe for ripening. In the past couple of days, the oiled fruits suddenly swelled and one is hanging flaccidly, ready to be harvested.
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Ethylene’s magic is not restricted only to fig fruits, or even to fruits in general. Depending on timing and concentration, effects of this simple compound are far-ranging. For instance, ethylene was partially responsible for initiating the colorful display of autumn leaves a few weeks ago. Perhaps you have a houseplant whose leaves look uncharacteristically clenched and in pain. Ethylene again. Excessive watering could be the cause; roots gasping for air release a natural chemical that is transported to the leaves where it’s converted to ethylene. There, ethylene disrupts normal cell growth, with curling the result of cells in the upper part of the leaf outgrowing those that are below.
The swaying of stems under windy conditions — picture a pine growing on an exposed cliffside — also stimulates ethylene release which, in this case, results in stockier growth. I lightly brush the tops of my tomato seedlings in spring for the same effect.
This time of year, I’m paying most attention to ethylene’s effect on fruits, figs and otherwise. Apples, bananas, pears, and avocados put out a burst of ethylene just before ripening on or off the plant, and this ethylene stimulates further ripening with a snowballing effect. I keep my eye out for any damaged fruit in a bin or bag of fruits, because injuries further stoke the ethylene “fires,” speeding the transition from ripe to over-ripe. That’s why one rotten apple really can spoil the whole barrel.
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“Ripe,” for a fruit, can mean different things to different people. Some people leave rock-hard peaches and plums on their kitchen counters to “ripen.” But not every fruit ripens off the plant, even if picked at a near ripe state.
That burst of ethylene just before ripening is not characteristic of all fruits; just so-called climacteric fruits. With non-climacteric fruits, ethylene production just gradually increases as ripening occurs. Non-climacteric fruits, which include raspberries, sweet cherries, and strawberries, definitely do not ripen at all after being harvested.
Climacteric fruits do allegedly ripen — or, at least, soften, sweeten, and change color — after being harvested, as long as ripening is sufficiently imminent at harvest time. But is softening, sweetening, and color change all that a ripe fruit has to offer? No. A whole spectrum of flavorful aromatics is also waiting. Although some fruits might ripen to perfection harvested before fully ripe (tomatoes and late apples, for instance), and other fruits must be harvested underripe for ripening off the plant (European pears and avocados, for instance), many fruits, climacteric and non-climacteric, taste best if fully ripened on the plant.
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Fig is a climacteric fruit but one that I believe tastes flat if harvested anytime before it’s dead ripe. All of which made me most interested to taste my oiled fig. Would ethylene-induced premature ripening, from a single drop of oil in the eye of the fruit, result in a syrupy sweet, richly flavored Kadota fruit, such as I’ve harvested from my greenhouse tree in summer and fall, or would the fruit look and feel ripe, but lack full flavor. Drum roll . . . flavor is flat. (That flat flavor could also reflect the seasonal cooler and less bright conditions of this time of year.)