Cold Rules

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Water Freezes. Why Don’t Plants?

(The following is adapted from my book, The Ever Curious Gardener: Using a Little Natural Science for a Much Better Garden, available wherever fine books are sold, and my website.)

Not being able to don gloves and a scarf, or shiver, to keep warm, it’s a wonder that trees and shrubs don’t freeze to death from winter cold. They can’t stomp their limbs or do jumping jacks to get their sap moving and warm up. The sap has no warmth anyway.Trellis and snow

Sometimes, of course, plants do succumb to winter cold. But usually that happens to garden and landscape plants pushed to their cold limits, not to native plants in their natural habitats or to well adapted exotic plants. 

Think about it: water freezes at 32 degrees Fahrenheit—not a particularly cold temperature for a winter night—and plants contain an abundance of water. Water is unique among liquids in that it expands when it freezes, so you can imagine the havoc that could be wreaked as water-filled plant cells freeze and burst. Yet plants that must stand tall all winter do, of course, deal with frigid weather. 

A Helping Hand for Herbaceous Plants

Herbaceous perennials (non-woody plants) opt for the easiest survival route.Their roots are perennial but their tops die back to the ground each year. Anticipate cold weather, these plants start pumping reserve nutrients to their roots in late summer. That’s why asparagus, cone flowers, delphiniums, and peonies are reduced, in autumn, to nothing more than a few dry stalks. Mulched garden bed

What’s left of these plants spends a mild winter underground. Five feet down, the earth’s temperature hovers around a relatively balmy 50 degrees Fahrenheit.

Practical Rule #1: A thick blanket of some fluffy, organic material—leaves, straw, or wood chips, for example—further limits cold penetration.

Also for Woody Creepers

Low-growing, woody plants have it almost as good, with their stems shielded from the full brunt of cold winter winds. If Nature decides to throw down a powdery, white insulating blanket, so much the better: those leaves and low stems are protected even more. Lingonberry under snow

Practical Rule #2: In case Mother Nature is distracted with other activities, I provide my own low blanket for low-growing, woody or evergreen perennials—again, that fluffy cover of straw, leaves, or wood chips. Waiting to cover these plants until the weather turns relatively cold (soil frozen an inch deep is a good rule of thumb) lets plants acclimate to cold, and their stems and leaves have no chance of rotting beneath mulch that is still moist and too warm.

Tricks and Tips for Trees and Large Shrubs

What about trees and shrubs whose stems are fully exposed. One way they protect themselves from freezing is by shedding those parts most likely to freeze—their leaves.Blueberries and snow

Which introduces Practical Rule #3: I help plants along with their leaf shedding by letting plants naturally slow down and begin to reallocate their energy resources beginning in late summer. No water, fertilizer, or pruning at that time. 

Of course, their stems still have to stand up and face the cold. Their living cells are filled with water. If this water freezes, the cells either dehydrate or suffer physical damage from ice crystals. 

Water, whether in a plant cell or a glass, does not necessarily freeze as soon as the temperature drops below 32 degrees Fahrenheit. To freeze, water molecules need something to group around to form ice crystals, a so-called nucleating agent. Otherwise it “supercools,” remaining liquid down to about minus 40 degrees Fahrenheit, at which point ice forms whether or not a nucleating agent is present. 

All sorts of things can serve as nucleating agents—bacteria, for instance—so plants may not be protected all the way down to minus 40 degrees Fahrenheit by having their water supercool. But winter temperatures don’t plummet that low everywhere, so just a bit of supercooling may be all a plant needs to survive winter cold. 

Another trick, effective well below that minimum supercooling temperature, is for a plant to gradually move water out of its cells into spaces between the cells. As temperatures drop, ice crystals outside plant cells grow with the water they draw out of the cells; plants then are threatened by dehydration than by freezing. Plants toughest to cold are those that are best at reabsorbing the water outside their cells when temperatures warm. Kiwivines covered with ice

One other mechanism at work “freezing point depression,” which is why antifreeze keeps the water in your car radiator from freezing. Dissolving anything in water lowers the freezing point, more so the more that’s dissolved. As liquid in plant cells lose water, remaining water becomes more and more concentrated in sugars and minerals, its freezing point keeps falling. 

Plants actively prepare for cold, with cell walls increasingly strong and and permeable. Light supplies needed energy for all this, making Practical Rule #4 to make sure to site and prune plants for adequate light.

Unfortunately, all this fiddling with a plant to help it through winter palls in the face of genetics. The very most that I can do to help plants face winter is to plant those that naturally tolerate the coldest temperatures winter is apt to serve up.

Greenhouse Happenings, Figs and Lettuce and . . .

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Darkness Descending

Plant growth has come screeching (almost) to a halt. Lettuces just sit, hardly growing. No wonder, you are no doubt thinking. It’s getting colder and colder outside. I know that, but I’m writing about lettuces in my greenhouse. The issue isn’t lack of heat. It’s lack of light.Planting greenhouse lettuce

For more evidence that light is the issue, look to good vegetable gardens in southern Europe. In that mild climate, harvest from a well-planned vegetable garden continues year ‘round. But year ‘round harvest there takes planning — lack of light also makes for very slow growth over there in these darkest months. Unprotected plants survive because the winter weather never gets that cold over there. (And cool-season vegetables, such as spinach, radish, and turnips, that we plan for sprig or fall, are what do well in Mediterranean winters.)

My garden here in the Hudson Valley, at about the 42nd parallel, experiences winter day lengths the same as Rome, Italy or the island of Corsica — all on about the same 42nd degree of latitude. If lettuce plants grow slowly in Rome and Corsica, then the slow growth of lettuce in my greenhouse should come as no surprise. But it always does surprise me, and the brakes seem to start getting applied back in October, with full pressure about now.

All this came to the forefront of my attention back in 1992, when I read Eliot Coleman’s excellent book Four-Season Harvest. After highlighting the similar insolation of much of our “northern regions” with much of balmy Europe, he went on to describe various ways of protecting winter vegetable from our winter cold, which would kill most of them. Keeping the plants a bit warmer also gets them growing sooner once days become longer and brighter.

My goal, in the greenhouse, is to get a good share of the plants almost fully grown going into December. With lettuces, I try to plan to have enough of them to fill salad bowls through January and February, after which smaller plants are starting to grow fast enough to fill those bowls.

The 42nd Parallel

The reason Corsica and Rome remain relatively balmy all winter while winters here, with both locations at the 42nd parallel, get so frigid is that Corsica is bathed by the Gulf Stream, that warm mass of air that flows up from the Caribbean and across the Atlantic to wash over western Europe.

The warm touch of the Gulf Stream is lost as you move further east across Europe and into western Asia. Kazakhstan, parts of which also lie at the 42nd parallel, experience average annual temperatures from -60°F to 104°F!! The climate of nearby Turkey, whose north end touches that latitude, is moderated by the Caspian Sea. Moving further east to parts of Inner Mongolia, still within the 42nd parallel, winter temperatures might dip to -90°F.

A Greenhouse is not a Hothouse

If you were to join me in my greenhouse today, don’t forget your hat and gloves. The greenhouse is heated, but only minimally, enough to keep the temperature from falling below 37°F. That temperature provides a nice balance between energy use and reasonable year ‘round harvest. (Expotentially more energy is needed for incrementally increasing temperatures.)

Today is rainy and very cool, but not cool enough to kick on the greenhouse heater. So it’s pretty much the same temperature inside the greenhouse as outside the greenhouse — in the 40s. Most of what’s growing — kale, celery, mâche, claytonia, Swiss chard, mustard greens, parsley, and arugula — do fine with these conditions.

Leafy vegetables require less energy (i.e. sunlight) than do fruiting vegetables, so the low light is also fine to keep them happy even if only slowly growing, just as they would be planted (outdoors) in a garden in Corsica or Rome.

That’s also home to my baby, hardy cyclamens (about which I recently wrote), in a seed flat, until they decide to lose their leaves and go dormant. And two cardoon plants, also native to Mediterranean regions.

One Mediterranean plant that is very unhappy this year, even in the greenhouse, is fig. Figs are still ripening but, with the high humidity and low light, each is soon covered with fuzzy, gray mold. Figs rotting in greenhouseSplitting figRoots of Rabbi Samuel fig, near the endwall, spread under the wall and outside the greenhouse, soaking up so much water that the figs split before ripening. Yet, a few fig fruits escape both afflictions and ripen to juicy sweetness.

I wonder if fig gardeners in the Mediterranean share my fig problems.Eating a fig

Mo’ Plants

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Cyclamen Addict

I’ll admit to being an addict. But my addiction — to propagating plants — is benign. It pains me to throw away an interesting seed or pruned-off stem; either can grow into a whole new plant, anything from a charming little flower to a towering tree.

Cyclamen hederifolium, self-seeded

Hardy cyclamen self-sown seedling

Hardy cyclamen in pot

Hardy cyclamen in pot

Case in point are some cyclamen seeds I collected and sowed a couple of years ago. The mother plant is Cyclamen hederifolium, a species that differs from the large, potted cyclamens you now see offered in garden centers, hardware stores, even supermarkets. Cyclamen hederifolium is cold-hardy here, so comes back year after years planted outdoors in the ground, and it’s a dainty plant, with small flowers and commensurately small leaves. Otherwise it looks just about the same as the widely sold commercial species, the pink or white flowers hovering like butterflies on thin stalks above the whorls of variegated leaves.

Following those flowers are seed capsules, mostly hollow balls the size of small marbles each attached to the plant by a stem that is wound up like a spring. It was in the beginning of the growing season 2 years ago that I sowed the seeds in a seed tray filled with sterilized potting mix. (I don’t usually sterilize my potting mixes but I didn’t want weeds to interfere with the slow-germinating seeds.) Eventually the seeds sprouted and I kept them watered, as needed, for good, albeit slow, growth.

Hardy cyclamen’s flowers fade and leaves melt into the ground as plants ease into dormancy with the approach of winter. Not my seedlings, though. I learned, years ago, not to push them into dormancy; instead, keep them growing as long as they want to until they’re ready to start storing energy. Which I did, with plenty of light and, as before, water as needed.

This summer, the plants were still growing — and still small — and I noticed some swelling beneath each plant. Cyclamen herodifolium, small tuberThe youngsters finally were growing tubers, small bulb-like structures that will, in the future, store energy to carry the plants, dormant and leafless, through winter.

This time next year I expect my plants will be officially adult, with flowers as testimony to their maturity.

Little House Not on the Prairie

In her youth, my daughter periodically entered the world of Laura Ingalls Wilder, so the one acre, adjoining field we acquired became “the prairie.” Moving the playhouse I built out to the field would have completed the picture of “little house on the prairie.” The playhouse never got out there but the “prairie” — or “hayfield” — as I usually refer to it, has remained as such.

My affection for prairies came from my living 12 years in Wisconsin (and studying the rich soils — the richest in the world — underlying prairies). My daughter has long outgrown her prairie phase but I’m going to make my “prairie” more prairie-like. One plant for that purpose would be big bluestem (Andropogon gerardii), the star of the Big Four of grasses native to the tall grass prairies, the other three bering indiangrass (Sorghastrum nutans), switchgrass (Panicum virgatum), and little bluestem (Schizachyrium scoparium). Big bluestem is the tallest of the lot towering 6 to 10 feet high. It’s also good for hay and wildlife, and tolerates drought.

A few years ago I bought some big bluestem seeds and ended up with just a few plants. Those plants are now producing seed which — I can’t help myself — I’ve collected. Andrapogon, big bluestem seed headNot that some of the seeds wouldn’t self-sow near the mother plans, but seedlings that do sprout under natural conditions are subject to competition for light, nutrients, and water from other plants.

Like many fall-ripening seeds, big bluestem seeds won’t sprout as soon as they hit the ground; otherwise winter cold would do them in. So they need “stratification:” a false (or real) winter. For many seeds, cool, moist conditions, such as a few weeks residence in a mix of moist peat and perlite in a plastic bag in the refrigerator will do the trick. Big bluestem can also be coaxed out of its winter  slumber with cool, dry conditions. Perhaps I’ll try both ways.

Bluestem Addiction

My present tallgrass prairie is only about 4 square feet, from two seedlings I originally planted plus their slow underground spread with rhizomes. Over time, with my additional plantings and help — a once a year, late winter mowing (taken care of under natural conditions with fire) — my prairie will swell.

A prairie takes time, as does, though less is needed, raising cyclamen to flower from seed. That time element itself brings with it certain satisfactions, both with the process and the result. That’s fortunate, since patience is an important element in successful propagation of plants.

Upcoming workshop

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Drip workshop ad, 2018

Future Tense, Present Tense

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Past is Present . . . No! . . . Present is Future

Gardening is so much about planning for the future. Dropping seemingly dead, brown specks into a seed flat in spring in anticipation of juicy, red tomatoes in summer is fun and exciting.

But now, in the glory of summer, I don’t particularly like planning, which means thinking forward to the crisp days of autumn that lie ahead. But I must. I know that when that time finally comes, I’ll have had my fill of hot weather. And the cooler weather coupled with shorter days and low-hanging sun will have tomatoes, cucumbers, peppers, and other summer vegetables on the wane. Planning and action now let me have a whole other garden come autumn, a garden notable for its shades of green (from leaves) rather than the reds and yellows (from fruits) of summer’s garden.

I’ll need plants and free space ready for my autumn garden. Some plants are already in place: One bed has been home, since early spring, to kale, which keeps growing as we harvest leaves through spring and summer, and brussels sprouts, from which harvest won’t even begin until early October.

Cabbage plants sown in seed flats in early June are about ready to plant now out in the garden for autumn harvest. Today I sprinkled seeds of endive into mini-furrows in potting soil in a seed flat.Seed flats The endive seedlings will be ready to move out into the garden in 5 or 6 weeks. I’ve also sown more kale seeds to supplement the spring kale for harvest into and perhaps through (depending on the weather) winter.

Early August will be a good time, around here, for planting Watermelon — the Watermelon variety of winter radish, whose innards look like cut watermelon but taste very radish-y. Also turnips, the delicious variety Hakurei.

I’m also sowing lettuce seeds, which I’ve been doing since spring and continue to do every few weeks. They also go into seed flats, ‘GrowEase’ seed starters, from which I can pop out transplants into any spaces that open up here and there around the garden.

Looking for an Opening

So where am I going to plant all those endives, cabbages, winter radishes, and turnips? The autumn garden will also need room for direct sowings of quickly maturing autumn vegetables like arugula, mustard, and lesser known salad “greens” like mâche (corn salad), erba stella (minutina), and claytonia (miner’s lettuce). The garden is packed full of plants now.

Endive, radish, radicchio in fall

Endive, radish, radicchio in fall

Going into August, space will open up for those autumn garden plants. From my first planting in mid-May, I’ll pick the last ripe ear of Golden Bantam sweet corn around mid-August, then have a whole bed available as soon as I clear away the spent stalks. Similarly for the beds of onions, early bush beans, and edamame.

Black Raspberries (Blackcaps) Redux

Enough planning for autumn and beyond. I’m going outside to feast on blueberries, black raspberries, and gooseberries, for me the essence of summer.Black raspberry

Now that I think of it, as soon as the black raspberries finish up, which is very soon, I do have to plan for them also, for late summer and autumn. The varieties I grow — Niwot and Ohio’s Treasure — are unique in being two-crop black raspberries, just like my “fall-bearing” (“everbearing”) raspberries. That is, they bear in early summer on stems that grew last year, just like conventional black raspberries. But — and here is where they are unique — they also bear in late summer and autumn beginning at the tips of new stems that rose from ground level this spring.

Last year’s stems are just finishing fruiting, after which they begin to die. I’ll cut them away to make room for the new stems and to keep the late summer and autumn harvest from these new stems from becoming a thorny nightmare.Black raspberry fruit

Berries Begin

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Green Thumb Not Necessary

Every day, for some time now, my strawberry bed has yielded about five cups, or almost 2 pounds of strawberries daily. And that from a bed only ten feet long and three feet wide, with a double row of plants set a foot apart in the row.Strawberry harvest
Good yield from a strawberry bed has nothing to do with green thumbs. I just did what’s required to keep the plants happy and healthy. To whit . . .

I planted the bed last spring to replace my five-year-old bed. About five years is about how long it takes for a strawberry bed to peter out due to inroads of weeds and diseases, including some viruses whose symptoms are not all that evident.

To keep my new plants removed from any problems lurking in the old soil, I located the new bed in a different place from the old one. Further forestalling problems, plants came not from a generous neighbor and not from my old bed, but from a nursery selling “certified disease-free” plants.

I chose to grow them in a “spaced plant” system (which does not involve getting plants high, ha, ha) but allows each plant a square foot of space. Throughout the growing season, I clipped off any runners and daughter plants attempting to establish themselves and crowd into the mother plant’s space.

Other growing systems allow for runners, which makes for more economical planting of a bed but reduced initial yield. Given free rein, though, new plants eventually become the worst weed in any strawberry bed; they must be dealt with in some way.

Did I mention that the new bed, like the old one, was in the vegetable garden, where the soil is rich in nutrients and organic matter, with plants’ thirst quenched daily via drip irrigation? 

In late December, when the ground had frozen about an inch deep, plants were snuggled beneath mulch as protection from winter cold. Straw, pine needles, wood shavings — any loose organic material will do.

Come spring, just as soon as plants began to awaken, I pulled back new growth beneath the mulch and tucked it under the plants’ leaves. I also trimmed off any dead leaves. The new job for the mulch was then to keep the soil moist and the soon-to-form ripening berries clean of soil.

That’s it, for all those berries, fresh picked every morning. Every morning for a little while longer, that is. I planted a “junebearing” variety of strawberry, Earliglow, known for earliness and good flavor, but bearing only for a few weeks in June. Other varieties, so called “everbearing” and ”day neutral” varieties, bear repeatedly through the season.
Netted strawberriesOnce Earliglow stops bearing for the season, the bed will need renovation and, through the season, its runners pinched off weekly to keep each plant “spacey.”

Better Berries

You might wonder: Why such a relatively small planting of strawberries, and why only junebearers? This admission may be sacrilege: I’m not a big fan of strawberries. I like the fruit well enough, but mostly because they are the first fresh fruit of the season.

(One other fruit does beat out strawberries as the first fruit of the season. They are honey berries, a kind of edible honeysuckle. Their flavor, thus far, has not impressed me. Breeding and cultivating honeyberries is in its infancy. They’re perhaps where apple was 2000 years ago, and the future might bring more flavorful ones.)

Back to strawberries . . . another of their deficiencies, in my view, is that you have to crawl for the fruit. And, as mentioned previously, although technically perennial, beds should replanted in a new location every 5 years or so.

The Best Berries

The fresh strawberries came on the scene on the tails of last year’s frozen blueberries, one of my favorite fruits. Perfect. (The loss of frozen blueberries is softened by the freshness of the strawberries.)

Last frozen blueberries, fresh picked strawberries

Last frozen blueberries, fresh picked strawberries

And just as the fresh strawberries fade out for the season, fresh blueberries will begin yielding this season’s bounty. Also, at the same time, black currants and red currants. And then black raspberries, and then  . . . and on and on.

All You Need To Know About Blueberries

Interested in growing your own blueberries? It’s easy, if you meet their basic needs, all of which, including varieties, harvest, and other pressing questions about growing blueberries, will be covered at my upcoming BLUEBERRY GROWING WORKSHOP. The workshop will take place on my New Paltz farmden on July 22, 2018 from 9:30-11:30am, at a cost of $48. Registration is a must. For more information and registration, go to www.leereich.com/workshops.

Bedding Down

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Flat Beds

My vegetable garden is in beds. Your vegetable garden is in beds. Seems like just about everybody plants in beds these days. And with good reason. Beds make more efficient use of garden space. Soil compaction is avoided because planting, weeding, pruning, and harvesting can be done with feet in the paths. And the shapes of the beds can help make even a vegetable garden look prettier, especially with decorative plants edging the beds. 

Raised beds are also one way to grow happy plants in otherwise poorly drained ground, or in ground that has been contaminated by lead or arsenic. Such contamination is likely to occur from past use of leaded gasoline near roadways, from old paint near buildings, and from residual pesticides in sites that were once orchards.

My vegetable garden is laid out in 3-foot-wide beds with 18-inch-wide paths between them that feed into one 5-foot-wide path down the center of the garden. Many gardeners, when considering planting in beds, equate that with RAISED beds. My vegetable beds are not intended to be raised even a hair above the paths.My garden's beds

When I began my garden, I laid out the beds and covered them with compost, and then laid wood chips from local arborists in the paths. The difference in appearance of the two materials makes it easy to see where to walk and where not to walk. (For most people, that is. A well-known food writer once visited my garden. As I walked up a path, he tromped along next to me — right up the middle of the bed adjacent to the path! — until I let out a scream that brought him to an abrupt stop. Some lush plants in the bed were admittedly flopping onto the path, obscuring the difference between walking and planting areas.)

Raised Beds

Soil in raised beds is usually held there with boards or other edging. That edging material might itself be decorative: lumber, bricks, roof tiles, or, in a “colonial” garden, logs.Garden beds

Ideally, any wooden edging is rot resistant. Locust or redwood would be my top choices, but hard to get. “Manufactured” lumber, such as Trex, is another possibility. Then again, pine or spruce boards are readily available, relatively inexpensive, and should last quite a few years.

A six-inch-high bed provides enough well-drained root depth for pretty much all vegetable plants. 

One disadvantage to raised beds is that you have get soil to fill them up. That soil could, of course, come from what will be the paths. Metal edged raised bedsIf the area is wet, though, taking soil from paths is going to lower them, making them that much wetter.

Most people bring in soil for raised beds, and, in the interest of having the best possible garden, make that “soil” compost. Not a good idea. For one thing, compost is mostly “organic matter,” meaning compounds of carbon, hydrogen, and oxygen. With time, as organic matter decomposes to nourish soil microorganisms and plants, it disappears, literally, becoming carbon dioxide and water. So a raised bed filled with compost will eventually shrink down to almost nothing.

The thing to do is to fill beds almost to their brims with any any well-drained soil. Fertility is not important; that will come from the one to two inches of compost with which the soil is topped. Replenishing the compost each year will provide all the nutrition plants need for that year; no additional fertilizer is necessary. And no need to dig or rototill the compost into the ground.

One more thing about raised beds: The improved drainage also means that they dry out faster, so benefit from irrigation.

Table-like Beds, Not

If you were to walk into my garden, you might notice that my planting beds are indeed a bit higher than the paths. This was not deliberate.

Each year for many years I’ve topped all my beds and an inch or two of compost.Dog Sammy and garden beds Paths get replenished with wood chips only if they start to get weedy or bare soil starts peeking through.

If it weren’t for decomposition, those yearly additions of compost would have made each bed into a “table” more than three feet high. It hasn’t. Q.E.D.

(Micro)climate Change

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As the train rolled southbound along the east bank of the Hudson River, I took in the varied landscapes along the opposite west bank. Spilling down the slope to the river on that bank at one point was what appeared, from a distance, to be a vineyard. I was envious.

(I never could understand why the region here is called the Hudson Valley. Along much of the Hudson, the land rises steeply right up from river’s edge. Where’s the valley?)

I wasn’t envious of the riverfront site of the vineyard property. I wasn’t even envious of having a whole vineyard  of grapes. (I cultivate about a dozen vines.)

What I did envy was the microclimate of the site. Microclimates are pockets of air and soil that are colder, warmer, more or less windy, even more or less humid than the general climate, due to such influences as slopes, walls, and pavement. 

The vineyard was not that far from my home, but the microclimate was worlds apart. Every parcel of land, from a forty-acre farm field to a quarter acre lot, will have some microclimates, and siting plants with this in mind can spell the difference between whether or not they thrive or even survive. Microclimate, early tulipsI’m banking, for instance, on the slightly warmer temperatures near the wall of my house to get my stewartia tree, which is borderline hardy here, through our winters. (It has.) And I expect spring to arrive early each year, with a colorful blaze of tulips, in the bed pressed up against the south side of my house. Proximity to paving also warms things up a bit.

Microclimate for cold, microclimate for warmth

Microclimate isn’t always about trying to keep a plant warmer in winter, or speeding up growth in spring. It’s also useful for keeping plants cooler. By training my hardy kiwifruit (Actinidia spp.) vines right up against the shaded, north sides of their hefty supports, I keep the sun off their trunks in winter and avoid the splitting that occurs when trunks are warmed during winter days, then precipitously cooled as the winter sun drops below the horizon. Microclimate, lingering snowBy planting the coveted blue poppy in a bed on the east side of my house, I hoped to give the plant the summer coolness that it demands. (That east bed was still too sultry; the plants collapsed, dead.)

Microclimates are important when growing fruit plants that blossom early in the season because frozen blossoms do not go on to become fruits. Early season bloomers need microclimates that are slow to warm up.

South facing slopes stare full face at the sun, so these slopes warm up early in spring and are warmer in both summer and winter. Therefore, a south facing slope—even if the grade is only slight—can be used to hasten fruit ripening on a plant like persimmon, which blooms late but needs a long season when grown near its northern limits.

Right after I push soil over the first seeds of sweet corn that I plant, I firm it over that hole with my foot at an angle to make a south-facing depression in the ground. That mini-slope will warm up just a wee bit sooner than flat ground.

The sun glances off north slopes, delaying their warming in spring and keeping them cooler in summer. Such a microclimate is ideal for an early blooming fruit tree like apricot or peach, and for plants, such as sweet peas, that enjoy cool summer weather. Likewise ideal for such plants is near the north side of a building, where shade remains through winter and the early part of the growing season.

If a slope actually has some elevation to it, the air is going to cool by one degree Fahrenheit every three-hundred feet going up the slope. If I had sloping ground, which I don’t, and sought a cooler location for planting, I’d avoid planting at the very top of the slope, though, because the upper reaches are usually windy.

A cold spot, here

Ideal vineyard site, from plant perspective, in Germany

Counterintuitively, the very bottom of a slope will also be a cooler microclimate. On nights when the sky is clear, with no clouds or leafy trees to block re-radiation of the sun’s heat from the ground back to the heavens, the air at ground level cools. An “inversion” occurs, with warmer air higher up. The cold air, which is denser than warm air, flows downhill to settle into depressions, just as a liquid flows downhill. A low point would be the worst possible location for planting strawberries, which grow near ground level and whose early blossoms are threatened by late frosts in spring. Any dense fence or shrubbery on a slope stops the downward flow of cold air, which will pool, just as dammed water would, near the upper side of the barrier.

Among the fruits I grow are apples, peaches, plums, and pears, all of which tend to bloom early. My site, unfortunately, is just about the worst possible site for growing these fruits. Apple blossomsThe cold air that settles here on clear spring nights increases the likelihood of late frosts and also causes moisture to condense on the plants, leaving them more susceptible to disease. Hence my envy for that sloping vineyard site.

Check out my new book, The Ever Curious Gardener, for more on microclimate!!

Warm, Spring Weather is Coming

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Poppies in Snow

Snow today (March 7) — a perfect time to plant seeds outdoors. Yes, really!
Obviously, not just any seed can be sown in snow. The ground is still frozen solid so I can’t easily cover seeds with soil. And cold temperatures are going to rot most seeds before the weather warms enough for them to germinate and grow.

I’m planting poppy seeds. It does seem harsh to sow a flower whose seeds are hardly finer than dust and whose petals are as delicate as fairy shawls. But early sowing is a must, because poppy seedlings thrive during the cool, moist weather of early spring. Covering the seeds with soil? No problem: Poppy seeds sprout best left uncovered. And because poppies don’t transplant well, their seeds are best sown right where the flowers are going to grow.

I’ll be sowing annual poppies, whose petals and leaves are more delicate than those of Oriental poppies. Corn poppy (Papaver rhoeas) once dotted the grain fields of Europe with its blood red flowers.

corn poppy

Corn poppy

Corn poppies and pear trees

These flowers were immortalized in the poem Flander’s Fields, symbolizing lives lost in World War I. On Memorial and Veteran’s Day, red tissue-paper “corn poppies” are still distributed in memory of wars’ victims. Shirley poppy is a kind of corn poppy that has white lines along the edges of its petals. Corn and Shirley poppies begin blooming shortly after spring-flowering bulbs have finished their show, and continue blooming through July.

California poppy (Eschscholtzis californica) was named in honor of Dr. Eschscholtz, a Russian ship surgeon who found these bright orange flowers blanketing California hillsides. California poppy is a perennial but in our harsh winters must me treated like an annual and sown yearly.

Each winter, it doesn’t seem possible that the dust-like seeds I sprinkle atop the ground’s chilly, white blanket could ever amount to anything. Each spring, I’m amazed to see myriad of ferny poppy leaves, then flowers.

Warmer Spring in Greenhouse

The sun is getting brighter in the sky day by day so it’s mostly lack of heat that’s holding back plant growth. Outdoors, there’s not much to do about a lack of heat. In the greenhouse, it’s time to turn up the thermostat a bit.

Thus far, I’ve let greenhouse temperatures drop no lower than about 38 degrees F. During bright, sunny days, of course, temperatures push up into the 80s. Seedlings in greenhouseAn exhaust fan keeps temperatures from getting too high, which, with lows in the 30s, would wreak havoc with plant growth, at the very least causing lettuce, mustard, and arugula to go to seed and lose quality too soon.

Adding just a few degrees at the bottom end of the temperature scale will spur growth in the newly sprouting lettuce, arugula, onion, and leek seedlings. This new minimum temperature of 43 degrees Fahrenheit strikes a congenial balance between plant growth and the cost and conservation of energy, propane in this case.

Bottom Heat for Seedlings

I’m not skimping on heat when it comes to germinating seeds. Seeds require more heat to sprout than seedlings need to grow. Too little heat and seeds either rot or sprout too slowly.Heating mat
Fortunately, seeds need little or, in some cases, no light to sprout. Some people use the warmth atop their refrigerator for seed germination; the top of my refrigerator isn’t warm at all. Some people germinate their seeds at a warm spot in their house, such as near a heating duct; my home, heated mostly with wood, has no such oases. The temperatures near the wood stove swing over too wide a temperature range for good germination.

Years ago I invested in a thermostatically controlled heating mat, made especially for gardening. The mat is in the greenhouse, so even if greenhouse temperatures drop to 43 degrees F., my seed flats sit with their bottoms soaking up 75 degree warmth from the mat below.

That’s how much warmth is needed to get the pepper and eggplant seeds I sowed this week to sprout.

This Bud’s for You

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Swelling Buds

What an exciting time of year! After a spate of 50 plus degree temperatures, lawn grass — bare now although it could be buried a foot deep in snow by the time you read this — has turned a slightly more vibrant shade of green. Like a developing photographic film (remember film?), the balsam fir, arborvitae, and hemlock trees I’m looking at outside my window, have also greened up a bit more.

Going outside to peer more closely at trees and shrubs reveals the slightest swelling of their buds. Earlier in winter, no amount of warmth could have caused this. As a cold weather survival mechanism, hardy trees and shrubs are “smart” enough to know to stay dormant until warm weather signals that it’s safe for tender young sprouts and flowers to emerge.

These plants stay asleep until they’ve experienced a certain number of hours of cool temperatures, the amount varying with both the kind and variety of plant.

Once that cold “bank” has been filled, the plants merely respond to warming temperatures. Which, for many plants, is now.

Physiology aside, the buds provide an interesting winter diversion; look at their sizes, their shapes, their colors, and textures. (Admittedly, their interest would pale in the landscape exploding into flowers and leaves, when the buds anyway mostly disappear into flowers or leaves until later in summer when new ones re-form.)

More than just interest, buds are useful. Buds can be used to identify the kind of plant as well as whether flower buds are in the offing. Or perhaps that flower buds were in the offing but were damaged by winter cold.

Info from Buds

The first bit of information I glean from winter buds is plant identification. To begin, how are the buds arranged along the stem? Buds directly opposite each other, which is relatively rare for local trees, narrows the choice down to maple, ash, dogwood, and horse chestnut, or, as some people remember it, MAD Horse.

L to R: peach, pawpaw, fantail willow, viburnum, dogwood

L to R: peach, pawpaw, fantail willow, viburnum, dogwood

Of course, once I identify a tree as, for example, a maple, I have to look for other details, such as the bark, to tell if it is a red, sugar, silver, or Norway maple.

(A few less common trees also have opposite leaves, including katsura and paulownia, both non-native, and viburnums, some of which are native. Most shrubs have opposite leaves.)

Buds that are not opposite each other along a stem might be alternating along the stem, they might be whorled, or they might be almost, but not quite opposite, presenting a much wider field of plants from which to choose.

Then it’s time for a closer look at the buds themselves. Some plants—viburnums, for example—have naked buds, enveloped only by the first pair of (small) leaves, rather than the scaly covering protecting the buds of most other plants. Buds of plants such as maples have buds enclosed in scales that overlap like roof shingles. Or two or three scales might enclose a bud without any overlap, as they do on tuliptree.

Mature plants have two kinds of buds. Those that are longer and thinner will expand into shoots. Flower buds are usually fatter and rounder. I note how dogwood flower buds stand proud of the stems like buttons atop stalks — very decorative if you take the time to have a look. I take a look at a peach branch with its compound bud: a single, slim stem bud in escort between two fat flower buds.

Peach buds

Peach buds

Apple and crabapple flower buds occur mostly at the ends of stubby stems, called spurs, that elongate only a half an inch or so yearly. Pawpaws fruit buds are fat and round with a brown, velour, covering.

Practicalities aside, buds can predict what kind of flower show or fruit crop to expect, barring interference from late frosts, insects, diseases, birds, or squirrels. If peach fruit buds just sit in place rather than fattening as winter draws to a close, I’ll know that the night back in January when temperatures plummeted to minus 18 degrees Fahrenheit did them in, or at least some of them. 

More Winter Details

Back to winter plant identification and entertainment. Looking more carefully at these leafless plants promotes familiarity. Notice the intricacies of their various barks; shagboark hickory, sugar maple, persimmon, white birch, and, my favorite, hackberry,

Hackberry bark

Hackberry bark

are very characteristic. Note twigs’ color, presence of ridges or lenticels (corky pores), even their taste or aroma. The aromas of yellow birch (wintergreen aroma), sassafras, and black cherry (almond) practically shout out their identification.