MYCO-WHAT?
It’s Greek To Me (and You)
This far north, there’s only a little to do garden-wise this time of year, so let’s sit back and ponder the wonders of plant life. Mycorrhiza, to be specific. Wait! Don’t stop reading! Sure, the word “mycorrhiza” appears intimidating. But mycorrhiza are important in your garden, in the forest, to your trees and shrubs, maybe even to your houseplants.
First, the pronunciation. Say: my-ko-RY-za. It sounds nicer than it looks.
Now let’s take the word apart to see what it means. “Myco” comes from the Greek word meaning “fungus” and “rhiza” from the word meaning “root.” Mycorrhiza, then, is a “fungus-root,” an association between a plant root and a fungus so intimate that the pair has been given a name as if it was a single organism.
Mycorrhizal blueberry root
Win-Win
The association is symbiotic, beneficial to both parties. One end of the fungus infects a plant root, while the rest of the long, threadlike body of the fungus ramifies through the soil. Nutrients are absorbed from the soil by those fine fungal threads and pumped back to the plant. The result: mycorrhizal plants can draw nutrients and water from a greater volume of soil than can non-mycorrhizal plants, and plant nutrition is improved. To cite one practical demonstration of this benefit, agricultural scientists in California found that the presence of mycorrhiza was equivalent to the addition of more than one hundred pounds of phosphorus fertilizer per acre on citrus trees.
Another kind of mycorrhiza, in apple root
The mycorrhizal association might be termed a balanced parasitism; the fungus does exact payment for its services. Carbohydrates are, literally, the fuel of life, and though mycorrhizal fungi are adept at drawing minerals from the soil, they can’t make their own carbohydrates. So these fungi draw carbohydrates from their host plants, who can make it. Sunlight fuels the photosynthetic reaction of carbon dioxide and water into carbohydrates and oxygen.
Not all fungi are mycorrhizal. Non-mycorrhizal fungi get their carbohydrates either by eating living things without returning the favor, in which case they are called parasites. Others eat once-living organisms such as wood, leaves, and dead animals, in which case the fungi are called saprophytes. Some fungi feed on either or both the living and the dead.
Myco-where?
Mycorrhiza are almost ubiquitous on the earth. Walk through the woods in spring or fall and most of the mushrooms you see on the forest floor are the reproductive structures of mycorrhizal fungi, periodically popping up through the ground to spread spores. Below ground, these mushrooms are connected to nearby tree roots by fine fungal threads.
The plant known as Indian Pipes (Monotropa uniflora) offers an eerie signal of the presence of mycorrhizae below ground. This plant, with one nodding flower, is thoroughly white, lacking any chlorophyll with which it could use sunlight to fuel its growth. Instead, its roots tap into a specific mycorrhizal fungus whose underground threads are also tapped into the roots of a nearby tree. Indian pipes is a parasite; it takes from the fungus and the tree, offering nothing in return.
Indian pipes
Mushrooms are formed only by certain types of mycorrhizal fungi. Most mycorrhizal fungi are not so obvious, working unobtrusively in association with the roots of the vegetables and flowers in your garden, your lawn, shrubs, and trees. The gourmet’s truffle is the underground reproductive structure of one type of mycorrhizal fungus.
Most plants on our planet are infected with mycorrhizal fungi. Mycorrhiza are absent only in special situations such as in the acidic, nutrient-poor spoils left from mining operations, in agricultural soils that have been sterilized to kill pests, and in sterilized potting soil in flower pots. Certain plants never become infected; cabbage, spinach, buckwheat, and their relatives, for example.
The Practical Side
The importance of mycorrhiza is not diminished by their ubiquity. Mycorrhiza is a general term, and not all mycorrhiza are equal. A plant may be mycorrhizal, but perhaps not with the most effective species of mycorrhizal fungus or, perhaps, not enough of them. Mulching, fertilization, irrigation, chemical use and other gardening and agricultural practices alter the types and amounts of mycorrhizal fungi in the soil. Rototilling or turning over the ground, as you might imagine, disrupts those fungal threads. Except for high fertility, what’s good for plants — plenty of soil organic matter, growing plants, good aeration, adequate moisture — is also generally good for mycorrhizae.
Old-time gardeners would throw a handful of soil from an old apple tree into the planting hole for a new apple tree. A crude form of mycorrhizal inoculation? Agricultural researchers have tried to quantify why plants respond to inoculation with mycorrhizal fungi at one site, and not another. Which are the best fungi? What affects them? Recent research has shown that improved nutrition is only the most obvious effect of mycorrhiza. The mycorrhizal association also influences plant response to stresses such as drought, insects, and diseases.
As you might imagine, mycorrhizal fungi have been commercialized, available as inoculants or premixed into packaged potting soils. Under certain conditions, this might be beneficial. In many situations, it’s like “taking coals to Newcastle.” Usually, create conditions conducive to mycorrhizal formation, and a beneficial symbiosis will develop.
For my research as a graduate student, I studied the effect of, among other things, mycorrhizae in blueberry soils. Even my plants grown in sterilized soils in a greenhouse became mycorrhizal, which, while messing up that aspect of my experiment, did highlight how ubiquitous the association can be without the human hand.
If you want to lend your hand to the mycorrhizal association, you could actually extract and grow your own mycorrhizal inoculum. Read how, and learn all about mycorrhizae in Jeff Lowenfels’ excellent book Teaming with Fungi: The Organic Grower’s Guide to Mycorrhizae.
At any rate, mycorrhiza is a fascinating demonstration of ecology, the interrelationship of organisms on the earth.
MY VINES GET IN ORDER
Pruning vs. Training?
A long time ago, when I first started growing fruit trees and vines, I read a lot about the all-important pruning and training they require. But I couldn’t get clear on my head what exactly the difference was between “pruning” and “training.” I went on to learn that and a whole lot more about pruning (through books, as an ag researcher for Cornell University, and with practical experience), and eventually wrote my own book about pruning, hoping to present the techniques with more clarity and completeness than all the books I had read. Perhaps my book, The Pruning Book, does that.
Okay, to answer my question of yore. “Training” is developing the young plant to a permanent framework that is sturdy and will always have its limbs bathed in light and air, and whose fruits hang within easy reach.
Kiwifruit within easy reach
Training involves some pruning as well as coaxing stems to grow in certain directions. Once a fruit tree or vine’s training period ends, it generally only needs annual pruning.
Vine-y Training
I thought of all this today as I pruned hardy kiwifruit and grape vines. Both fruiting vines have been trained and are pruned similarly, with one slight variation that I’ll soon mention.
The kiwi and grape vines are trained as “double cordons” which are permanent arms sitting atop a trunk. They run in opposite directions along the middle wire of a 5-wire trellis, the wires parallel and supported about 6 feet of the ground on the cross-arms of T-posts. Each young vine was planted next to a metal or wooden stake to which the plant’s most vigorous stem was tied.
Once that trunk-to-be reached up to the middle wire, I tied it there and cut off all other stems. That trunk-to-be does, of course, keep growing; that new growth gets bent over and tied along the middle wire. Bending coaxes new buds to burst just beneath the bend, one of which is also bent over and trained along the middle wire in opposite direction to the first stem. Both these horizontal stems became the cordons, permanent arms of the plant. Growing off at right angles to the cordons are the fruiting shoots which, weighed down with their weight of fruit, drape onto the other wires.
Vine Maintenance
Today I’m maintenance pruning vines whose training period ended years ago. Maintenance pruning a mature fruiting vine keeps it bearing high quality fruit within easy reach year after year, all accomplished with a renewal method. That is, except for the trunk and the cordon, the vine is completely renewed with each year’s pruning.
I’ll admit it: A vine looks like a tangled mess before being pruned. But step by step, it begins to take shape and make sense. 
Knowing how a plant bears fruit is important in maintenance pruning. Kiwi and grape vines bear on new shoots growing off one-year-old stems. Kiwis bear best if those one-year-old stems are about 18 inches long. Grape one-year-old stems can be left long or short, but for my method of training, I want each one about two buds long, which is just a few inches.
Fruiting grape shoots emerge from 1-yr-old stem
Step one is a no-brainer. The outermost wires are 4 feet apart so I lop all growth back to just beyond those wires. My tool of choice for this is a battery-powered hedge trimmer although pruning shears would also do the trick, except at a snail’s pace.
Step two is to remove excess growth, which does two things. It removes potential fruits so that more of the plant’s flavor-rich goodness gets funneled into those that remain, and it decongests the plant. For this step, I cut back all stems 2 years or older.
But wait! Two-year-old stems have one-year-old stems, the stems needed for bearing shoots, growing off of them. So rather than cut a two-year-old stem all the way back to its cordon, I cut it back to a one-year-old stem originating near the cordon. Some one-year-old stems also grow right from the cordon. The best one-year-old stems are those that are moderately vigorous and, of course, look healthy. Moderately vigorous stems, for grape or kiwi, are about pencil thick (if you can remember what a pencil looks like; if not, about 1/4” thick).
Kiwi stem and pruning detail
There will always be too many one-year-old stems for the plant to make tasty fruit. So I reduce the number of potential fruits by removing some of the one-year-old stems, enough to leave six to ten inches between them on each side of a cordon.
Pruned grape vine
Not finished yet. The final step is to shorten the fruiting shoots. For hardy kiwis, I cut them back to 18 to 24 inches long. For grapes, to about 2 buds or a few inches long.
Oh, one more thing to do: I prune off any new growth rising up from ground level or along the trunk lower than the cordons.
And one more thing: I step back to admire my handiwork. (Here is a video of me pruning a kiwi vine.)
But What About Bushes?
You might have noticed, early on, that I wrote about pruning and training “fruit trees and vines.” What about blueberries, currants, gooseberries, elderberries, and other FRUITING BUSHES. Yes, they need annual pruning also. No, they do not need training. Although the plants are perennial, their stems are evanescent, all with a limited life. They are pruned by a renewal method — at ground level. All this and much, much more (pruning ornamental plants, houseplants; creating and caring for an espalier; how to scythe; etc) in The Pruning Book, of course.
LOOK BEYOND POINSETTIA GLITZ
A Harem of Males
Phew, what a year 2020 was! Well, it’s over and, at least at this writing, things look hopeful for the future, at least from my perspective. Except if you live in a tropical or subtropical climate, there’s not much distraction from anything gardenwise, for now, so let’s take a close look at a plant no doubt sitting on many coffee tables and windowsills. Poinsettia. I’m not a big fan of their appearance, but I do like them as botanical curiosities.
Let’s share some botanical lore of this plant by setting your holiday poinsettia on a table in good light for a close look at its flowers. I say “close ” because the flowers are not those large, red, leaf-like structures. The large, red, leaf-like structures are just that — leaves, albeit modified leaves called bracts. The bracts attract pollinating insects to the plant.
The actual flowers of the poinsettia, which are not very showy at all, originate within the small, greenish, cup-shaped structures you see above the bracts. These cup-shaped structures are “cyathiums.”
Each cyathium contains a single female flower surrounded by a harem of males. Pluck a cyathium from the plant, take a sharp knife or razor, and slice it in half from top to bottom. A magnifying glass helps now. You’ll see that the inner wall of the cyathium is lined with numerous tiny flowers which, when the flower is mature, protrude up through the opening of the cup. These are all male flowers.
Look very carefully and you’ll also see a stalk attached to the very bottom of the cyathium, protruding up through the cup opening, and capped by what looks like a turban. That is the single, female flower, which, to promote cross- rather than self-pollination, emerges from the cyathium after male flowers begin to shrivel. Cross-pollination promotes genetic diversity for healthier plants.
In addition to the male and female flowers, on the outside of the cyanthium is a single yellow gland that looks like the mouth of a fish poised to ingest food.
Next time a friend comments on the beauty of your poinsettia flower, take out a magnifying glass and closely examine a few cyathiums before looking up and agreeing nonchalantly.
Fool the Plant
Have you ever wondered how stores always manage to have blooming poinsettias for the holiday season?
Poinsettia, along with chrysanthemums and most strawberry varieties, is a “short-day” plant. Short-days induce “short-day” plants to form flower buds. (In reality, plants are responding to long nights, but the phenomenon was originally thought to be daylength dependent, and the term “short-day” plants has stuck with us.) Poinsettia can be fooled into blooming at any time of the year merely by exposing it to artificially shortened days.
To secure blooming plants for this past holiday season, poinsettias grown in large commercial greenhouse ranges were covered with a shade cloth so that they experienced 14 hours of darkness each “night” beginning around September. After 8 weeks of this treatment, they formed flower buds which became fully developed just before the holiday season.
You Do It
You can do this at home to make this year’s poinsettias bloom again whenever you want. Your poinsettias first will need a rest period. Loss of leaves and fading flowers indicate that your plants are entering dormancy. (Even tropical plants, such as poinsettia, do take a short, mild annual rest.) When the plants become dormant, move them to where it is cool. Water them infrequently, just enough to keep their stems from shriveling.
About April, the plants will be ready to start growing again. Cut the stems back to a few strong shoots, each about 6 inches long. Give the plants sun, warmth, and water. New shoots will push forth from dormant buds. When warm weather has settled, you can put the plants outside.
As temperatures cool in late summer, bring the plants indoors to a sunny window. Keep them away from cold drafts, which would cause their leaves to drop.
Now for the photoperiod treatment. Beginning three months before you would like the plants to bloom, make sure the plants get 14 hours of darkness each night. Moving them into a dark closet or covering them with a paper bag are convenient ways to do this.
The dark period each night must be uninterrupted. Even peek at them with a flashlight at midnight will have them acting as if they had a short night, instead of the needed long night.
After 8 weeks of the above treatment, move the plants back to their sunny window. Flower buds should be evident, and you should have blooming poinsettias within a month. If you want bloom for the holiday season next year, start the photoperiod treatment about the middle of September.
Poisonous?
Poinsettia, Euphorbia pulcherrima, is a member of the Euphorbiaceae family, commonly called the Spurge family. A common characteristic of plants in this family — which includes Hevea braziliensis, tapped commercially to make rubber — is the milky sap they exude when cut. The sap has often been considered poisonous and was sometimes used medicinally as a purge (hence “spurge,” from the French word espugier, meaning to purge). But, as Philippus Aureolus Theophrastus Bombastus von Hohenheim, more commonly known as Paracelsus, wrote in the 15th century, “All things are poisons, for there is nothing without poisonous qualities. It is only the dose which makes a thing poison.”
In fact, the sap is only mildly poisonous to humans and other animals. It can cause a rash on the skin or mouth, and stomach upset. So go ahead and nick the stem of your poinsettia and see the milky sap exude. No need to touch it.
