Mystery Solved, and Frigid Dealings

Mystery Plant: No longer a Mystery

Last week I mentioned my brother’s mystery shrub, which he wanted to prune back heavily. I told him it was okay to do so even though I — and a number of experts I consulted — could not identify the plant.

(Drum roll . . .) The plant has finally been identified, by Mark Brand of the University of Connecticut, as Wilson rhododendron, Rhododendron x laetevirens. I had narrowed it down to R. carolinianum, which is one of the parents of this hybrid, the other being R. ferrigineum.

Wilson rhododendron flower bud

Wilson rhododendron flower bud

My brother’s not noticing flowers on this rhododendron is understandable. It’s a super cold hardy but sparse bloomer that’s grown mostly for its foliage; the pointy leaves don’t droop or curl, but remain perky, even in frigid weather.

Now I can sleep nights.

It was Cold Outside!

Talk about frigid weather: I was surprised at how cold it was on the farmden during my Thanksgiving visit to my bro’ in Rhode Island. The night of Friday, November 23rd, New Paltz weather reported a low of 7° F. Brrrrr. As I’ve mentioned before, I live in a valley. Cold air, which is heavier than warm air, sinks into low spots, bringing the temperature right out in my garden even lower, down to 3° F.

(I knew this even when in Rhode Island, thanks to Sensorpush, a nifty device that transmits minute by minute temperature and humidity conditions to my cell phone from wherever the device is located.)

It’s all about microclimates, which are localized differences from the general climate due to such influences as heat-absorbing masonry walls and paths, which keep temperatures warmer in winter. Or nearby bodies of water, which keep temperatures warmer in winter and cooler in summer. Or differences in elevation, lowering the temperature 6°F for every 1000 feet of elevation, and low lying areas.

Lower temperatures with elevation might seem contradictory to the locally colder temperatures in my garden that night. These colder temperatures occur only when still windless air and a clear sky let any heat the ground has accumulated by day re-radiate back to the heavens. A cloudy night or tree cover would reflect that re-radiated heat back downwards, preventing the cooling. With radiative cooling, air near the ground is coldest, and and warmer air hovers higher up.

Microclimate Adjustment=Fresh Salad Greens

As a gardener, I can play around with microclimate and have it work for me, as evidenced from the fresh endive, winter radishes, lettuce, and turnips just harvested from right out in the garden.

Preparation for that harvest began in late summer with spreading compost in the bed and the sowing of endive seeds. I planted turnip, lettuce, and winter radish seeds in the bed in September.

Back in early October I spaced metal hoops 4 feet apart along the bed, each one spanning from one side to the other of the bed. Later on in October, I covered the hoops with a length of clear plastic, slitted row cover creating a tunnel over the bed. The slits keep the interior of this mini-greenhouse from overheating.Tunnel, clear plastic, vented, closeup

Moving into November, temperatures gradually cooled but still not enough to threaten the covered plants. Between the plants natural cold hardiness and the cover, I figured they were fine into the low 20s. (For more on microclimates and their manipulation, see my new book The Ever Curious Gardener.)

Short days and low hanging sun, coupled with cool temperatures, were not providing conditions for plant growth. But the plants were, by then, fully grown, so no more growth was needed. At that point I laid a cloth cover over the tunnel to keep out further depths of cold. Light became immaterial; I just wanted the plants alive and fresh.Tunnel with covers, Dec, endive revealed

And so they have remained, even after temperatures plummeted to 3°.

Not only are the plants alive and fresh. Cold temperatures have brought out the best in their flavor. The veggies are crisp, sweet, and tangy.Turnip from tunnel

(Micro)climate Change

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!!


Half a Pear, Tree

   Perhaps last winter’s weather — extended cold, but not frigid temperatures, and hardly any snow — is still playing games with us. Perhaps it is mischief from the early, extended, very warm weather in early spring that was followed by plummeting temperatures and our biggest snowfall (4 inches) of the year. Whatever the reason, some weird things are going on this growing season.Half dead pear tree
    Look at one of my old pear trees, for instance. This tree might be called my “sample” or my “first cut” pear tree. When I hear tell of a pear variety that might be worth growing, I get a scion and graft it onto this tree. The scion bears quickly, in theory, at least, and, if it passes the “first cut,” perhaps it will warrant its own tree. There’s not enough time or space to put every Tom, Dick, and Harry of a pear variety on its own tree.
    The tree now has about a dozen varieties of pear growing off various branches. That’s not weird, though. What is weird is that, right now, the top half of the tree is fully leafed out while limbs on the bottom half of the tree are leafless.
    A disease? Doubtful. A disease killing that much of a tree at once would probably originate in the trunk or roots, in which case the whole tree or only the upper portion would be leafless. And anyway, those leafless limbs are not dead. Cutting beneath the bark reveals living, green tissue.
    My hypothesis — a weak one — is that the cold snap in spring, where temperatures in the ‘teens followed a spate of temperatures in the 70’s, is the culprit. Warm temperatures in late winter and spring cause plants to rapidly awaken and lose the cold-hardiness they maintained through the coldest parts of winter. The pears seemed quite awake when that cold spell struck.
    But why was only the bottom portion of the tree affected? (Here’s the weakness in my hypothesis.) Windless, clear nights, such as during spring’s cold snap, bring a temperature inversion. Under such conditions, denser cold air can settle down near ground level. Even a few feet of elevation can make a difference, one that’s evident when riding a bicycle or motorcycle on a clear summer night on rolling terrain.
    So maybe the bottom half of the pear tree experienced temperatures just below the tipping point where enough damage occurred to delay leafing out.

Other Pear Trees, Still Whole

    No other plants, including other pear trees, experienced this bifurcation. Then again, the “sample” pear is all by itself where the microclimate might be slightly different.
    During that cold snap, the other pears were quite awake, seemingly just about ready to spread their blossoms. I was braced for a total crop loss. Weirdly, the trees went on to blossom just fine and now have what’s shaping up to be a decent load of fruit on them.

Seedling Troubles

    More weirdness: Every season I sow vegetable seeds according to a schedule I’ve developed over the years. I sow the seeds in mini-furrows in flats of potting soil or potting soil topped with a mix of peat moss and perlite. Every season I make my own potting soil from a mix of equal parts peat moss, perlite, compost, and garden soil, with everything sifted together through half-inch mesh hardware cloth.
 Sickly tomato seedlings   And every season I’ve had sturdy, lush green transplants to set out over the past few weeks. Not this season. Too many of the transplants are stunted, with flaccid leaves that are not uniformly lush green. Some have slight, interveinal yellowing of oldest leaves, some have slight reddening of veins, hinting, respectively, at insufficient nitrogen and phosphorus uptake .
    As usual, the weather could be blamed. Those auspicious, sunny days of late winter gave way to a long period of overcast days. Rain or not is not the issue because seedlings were in the greenhouse, watered as needed. Overwatered? Underwatered? Cool greenhouse temperatures could limit root growth, in turn limiting uptake of nutrients even if they are in the soil.
    The potting soil could be the culprit. Although ingredients of my mix are always proportionately the same, the compost isn’t exactly the same from year to year. Same goes for the “garden soil” that goes into the mix. I scrape it up from various places around the yard: the bottom of a finished compost bin, from my catch-all extra soil bin, from top layers of a pond I’m occasionally hand-digging.
    A couple of other gardeners and farmers have concurred with their seedlings’ poor growth this year. Perhaps it was the weather? Do you want to weigh in?

And the Winner Is . . .

    Very few people offered hypotheses on why only one limb of my plum tree was in bloom. Neither the weather nor any other environmental condition was to blame. In fact, I had grafted the tree a few years ago to four different varieties in order to spread out the harvest date and offer a greater variety of plum flavors.Plum, blossoming branch
    The bulk of the tree had already flowered.The one blooming branch was that of beach plum, the least reliable, smallest, and, to my taste, least flavorful of the lot. Perhaps I’ll graft that limb over to yet another variety.
    Congratulations to Tom,, on winning a copy of my book Grow Fruit Naturally.


Microclimates, Here, There, and Everywhere

    Mark Twain wrote that “Everyone complains about the weather but nobody does anything about it.” I’m going to step up to the plate and do something about it — not the climate but the microclimate. “Microclimate” is the very local weather. And I do mean “very local,” as, for example, right around a particular plant.
    Different microclimates exist all around my property — and yours. Near the south wall of my brick house for example, winter low temperatures don’t plummet nearly as low as they do, say, 30 feet away from the wall. The bricks are very good at absorbing the sun’s heat, then let it slowly ooze out after nightfall. Near that wall is where I’m planning to plant out a Kadota fig tree now dormant in my basement. (Come late fall, after harvest, I’ll dig up the tree with a good root ball and return it to winter quarters in the basement.) 

'Surround', a white clay, sprayed on apples

‘Surround’, a white clay, sprayed on apples

    On the other side of my house, where sunlight can’t fall in winter, days and nights are colder than the general temperatures, and remain colder from spring through fall. Near that north wall, then, would be a good place to plant an apricot or peach tree to delay unfolding of their blossoms, which otherwise open so early that they often succumb to subsequent spring frosts. Dead blossoms mean no crop for that season.
    Apricots and peaches, like most fruits need sunlight to fuel the most flavorful fruits. Although areas near the north wall are shaded — and hence cooler — in winter, from spring through early fall the sun wraps enough around the sky from the northeast to northwest corners to cast its light there.
    Other influences on microclimate include fences, land sloping in various directions, paved areas, plant or built windbreaks, and changes in elevation.

(Micro)Climate Modification

    Much of what I have planted, including many fruit plants, are nowhere near fences or paving, and my land is mostly flat. It is lowland, in a valley, and cold air, which is heavier than warm air, collects in this low spots, to threaten the blossoms on my fruit plants with late, killing frosts.
    Mark Twain notwithstanding, I’m going to try doing something about the weather — the microclimate, in this case — on plants nowhere near walls, fences, or paving.
    Enter ‘Surround’, the trademark name for a special formulation of kaolin clay. This product was developed about 30 years ago mostly as a nontoxic way to thwart insect pests. It’s especially useful for controlling plum curculio, a pest of plums, peaches, apples, and some other fruits; curculio isn’t easily controlled by other organic methods.

'Surround'  spray on blueberries

‘Surround’ spray on blueberries

   Kaolin is white, so when a sufficiently thick coating of ‘Surround’ is built up on branches, they appear white. Old Sol’s rays just bounce off white surfaces, the surfaces, in this case being the buds of fruit plants. So the buds stay cooler, delaying bloom, hopefully until after threat of frost has past.
    I’ve already given the plant a couple of coats of ‘Surround’, and they already have a sun-drenched, gray-cast, Mediterranean look to them. A couple more coats will make the visual effect more dramatic, both to me and Ol’ Sol, and will get a jump on curculio control.

Awake too Soon

    Downstairs, in the basement, things are not as quiescent as hoped. That’s where the figs, pomegranates, and mulberries are spending winter, the cool (45°F) temperature holding back growth. Or so I thought.
    One plant, Pakistan mulberry, has decided to awaken. This mulberry is a species of white mulberry (Morus alba) that differs markedly from the white mulberries you see here. Pakistan is only about as cold-hardy as fig (which is why they share winter quarters in my basement) and bears a very delicious, dark purple fruit up to three inches long!

'Pakistan' mulberry

‘Pakistan’ mulberry

    Pakistan evidently has a low chill requirement, that is, it does not take much cold for it to feel like winter has ended so it can begin growing. Different plants have different requirements for the number of hours of chilling, which is temperatures between about 30 and 45°F., they need to be exposed to before they can begin growth for the season.
    I may have to move the budding plant into the greenhouse where it really is spring, with temperatures at least into the 70s on this sunny day.