Inside and Outside
Houseplant Envy
I wonder why my houseplants look so unattractive, at least compared to some other people’s houseplants. I was recently awed by the lushness and beauty of a friend’s orchid cactii, begonias, and ferns. I also grow orchid cactii and ferns, so what’s with mine?
Perhaps the difference is that other’s houseplants have a cozy, overgrown look. Mine don’t. Most of my houseplants get repotted and pruned, as needed, for best growth. Every year, every two years at most, they get tipped out of their pots, their roots hacked back, then put back into their pots with new potting soil packed around their roots. In anticipation of lush growth, stems also get pruned to keep the plants from growing topheavy.
Rather than being scattered willy-nilly throughout the house or clustered cozily in corners, as in friends’ homes, my houseplants get carefully sited. For best growth, plants, especially flowering and fruiting plants, need abundant light, something that’s at a premium this time of year. So my houseplants huddle near south-facing windows like baby chicks near a heat lamp. And then in summer, when light, even indoors, becomes more adequate and the plants could move a bit back from the windows, I move them all outside so that summer sunlight, rain, and breezes can really get them growing.
What can I say? I’m too focussed on good growth, and that’s not necessarily what makes for the prettiest houseplant. It’s the difference between a lush plant packed into and overflowing its pot, along with elbow to elbow neighbors, versus one that’s had its soil refreshed frequently, its stems thinned out and pruned back, always with younger stems raring to grow. I can’t help myself.
Choice of houseplants also comes into play. Houseplants that are prettiest for the longest period of time — and need less light — are those valued for the shapes and colors of their leaves. I gravitate to houseplants with fragrant flowers or fruits, or — even better — fragrant flowers and fruits. Pumping out lots of flowers and, especially, fruits demands much more energy from a plant than just growing leaves. And that energy comes from sunlight and young leaves that are efficient at working with that light. Hence the repotting and clustering near sunny windows of my houseplants.
Perhaps it’s also a matter of the “grass is greener,” to me, in someone else’s house. I’ll start looking at my houseplants more with the eye of an appreciative visitor.
Winter Cold: The Good and the Bad
The temperature was 9° and we were on our way to go cross-country skiing when a friend asked if there was any benefit to the cold weather. Plantwise, that is. We knew the weather was good for skiing. Interesting question, and the answer is “yes.”
The first benefit that comes to mind is the effect of cold on diseases, certain diseases, at least. The cold kills them. Peach leaf curl, for instance, is a disease that overwinters in peach buds, resulting in leaves that unfold thickened and twisted and eventually yellow and fall so fruiting and growth suffer. Except in cold winters. My winters are usually cold enough so this disease is rarely a problem.
A number of summers ago late blight disease of tomato went on the rampage here and throughout the Northeast. That disease can’t spend the winter this far north because it’s too cold. In that past summer and some other summers, the disease hitchhikes north on infected plants brought here or, when winds and humidity are just right, hopscotches along north from one infected field to the next.
Insect pests that overwinter in the soil are more damaged the colder the soil gets, and bare soil gets colder than mulched soil, all of which highlights the balancing acts necessary in gardening.
Pests notwithstanding, bare ground isn’t good for plants and soil. Plant roots are more likely to be damaged by the increased exposure and, especially evergreens, are more apt to dry out because more water will evaporate from bare ground and because roots have a hard time drinking in water from frozen ground. Bare ground is also subject to erosion and nitrogen loss.
On the other side of the coin, bare soil goes through more cycles of freezing and thawing, which breaks up and moves around soil particles, in effect tilling the soil. Back to the previous side of the coin, that freezing and thawing can move soil around enough to heave plants, especially small or newly rooted plants, up and out of the ground.
So, I like cold weather for my plants. But I mulch heavily. And I especially like it, as do the plants — and, admittedly, some pests — when there’s an additional blanket of snow over the ground. It also makes for good skiing.
Snowy Skies & Winter Colors
Snow Outside but Color Inside
A day like this, a gray sky and six inches of fluffy, fresh snow laid gently atop the white already resting on the ground, hardly turns my mind to gardening or plants. Even the greenhouse, usually a cheery horticultural retreat in winter, is dark and cold. Snow on the roof blocks what little light peeks through the gray sky, and the heater doesn’t come alive until the temperature drops to about 37° F.
Carrots from jonnyseeds.com
And then I reach into my mailbox, and out comes summer! Seed and nursery catalogs oozing with photos of fresh carrots, heads of lettuce, juicy peaches, and sunny sunflowers. I’ve already ordered all my seeds, or so I thought until I started thumbing through more catalogs. Offerings in vegetable seeds, in particular, seem to get more interesting each year.
Take carrots, for example. Carrots have long been available in all sort of shapes and sizes. Nowadays, I can also buy seeds for white carrots (White Satin variety), carrots deep purple through and through (Deep Purple variety), and purple carrots with orange centers (Purple Haze variety).
Caulifower is also getting colorful. Its curds no longer need to be only white. The variety Cheddar is the color of orange cheddar cheese. Graffiti is a purple variety, unique among purple cauliflowers for retaining its color after being cooked. Years ago, I used to grow Violet Queen cauliflower, which turns green after being cooked and tastes very good.
I’m not saying that any of these interesting varieties taste better than less flamboyant varieties. Just sayin’ . . . they’re interesting.
Which Hazel?
Besides perusing summer-y seed and nursery catalogs, another antidote for a gray winter day is to get outside and enjoy it. I’m hoping to do that today, to glide through wooded paths on cross-country skiis.
No doubt I will come across plants flaunting winter weather and showing signs of life —even on this gray day. Native witchhazels, the so-called “common witchhazel” (Hamamelis virginiana), ocacionally still are showing off some of their strappy yellow flower petals. 
The flowers don’t exactly jump out at you so you have to get up pretty close to even notice them. Still, they are a sign of plant life in the depths of winter.
Common witchhazel typically begins blooming in September and finishes by December. How seemingly foolish! It’s been hypothesized that they bloom when they do so as not to compete with another species, vernal witchhazel (H. vernalis), where both are native. (This seems an unusual explanation because plant evolution is generally encouraged by cross breeding. That’s why an apple tree, for instance, can’t pollinate itself even though each of its flowers have both male and female parts; it has to cross with pollinate with a genetically different tree to make seeds and fruit.) Vernal witchhazel, at home in the midwest and south, begins blooming in January and might continue until spring.
Even without that competition, not much reproduction is going on with common witchhazel. It has a motley crew of pollinators: tiny wasps, fungus gnats, bees, flies, and winter moths. And even with all those matchmakers, less than 1% of flowers go on to form fruit and make seed. The seeds, 2 per fruit, are shot out of the fruits in autumn. After weevils, caterpillars, wild turkeys, and squirrels have had their fill, only about 15% of those few seeds survive. It’s a wonder that I come upon so many witchhazels in my winter glides and walks.
Looking over plant and garden notes from last year, I see that my cultivated witchhazel, the variety Arnold Promise, bloomed in my front yard in mid-March last year. That variety is a hybrid of Chinese and Japanese species. It blossoms later and its blossoms are much, much showier and more fragrant.
Sow Already?
Last year, sowing onion seeds
According to my notes, I’m due to plant onion seeds sometime soon. Yes, seeds. Seeds are the only way to be able to choose from the widest selection of onion varieties. Still, seeing witchhazel flowers will not be enough to well up in me an urge to plant anything. Tomorrow will be sunny; that should do it.
Update: Except that I chose the sunny day to go skiing instead. The onion seeds can wait. Growth is so slow early in the season that, come early May, there’s little difference in size among seedlings grown from seed planted now or within the next couple of weeks.
Cold Rules
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.
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. 
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. 
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.
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. 
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.
