First Published 4/28/2005
Extrafloral Nectaries

Frequently, I hear from gardeners who are a little annoyed about the ants crawling all over their peonies. Some worry that the ants are destroying the peonies, while others have equal disdain for the ants but tolerate them because of their long-held belief that the peonies need the ants to open their flowers. In fact, neither scenario is true; peonies not only tolerate ants, they could be called very close friends – all because peonies sweeten the deal with a little extra sugar.

A Stemful of Sugar

Any schoolchild knows that flowers produce sugar-rich nectar, the preferred food of bees, and that plants and bees cooperate in a kind of “work for food” program. The bees gather nectar to eat, but in doing so cover themselves with pollen, distributing it to other flowers, ensuring good seed production. But what’s not as commonly known is the fact that many plants produce nectar not only in their flowers, but also in specialized structures called extrafloral nectaries. These nectaries produce the sticky, sugary stuff that forms droplets or crystalline particles on peonies, as well as morning glory, willow, and exotic plants such as passionflower. The sugary stuff (commonly called sap) is indeed mostly sugar, but it may also contain small amounts of amino acids and trace amounts of various salts.

Extrafloral nectaries commonly form at the base of the petioles (leaf stems), and although they produce nectar similar to that of the flowers, it is often slightly richer. This enriched nectar is designed to attract not bees, but ants.

The Ants Come Marching In

Ants are generally very poor pollinators, so why would a peony want to attract them, especially when producing the sugar-rich nectar seems such a waste of a plant’s valuable food resources?

Well, many species of ants are predators. If a peony or passionflower can attract a few ants, those ants may feed upon, or at the very least fend off, marauding insects. Had the plant not first attracted these bodyguards with the extrafloral nectar, the ants would probably have looked elsewhere for food. The nectar is a small price to pay for protection from insect pests.

Extrafloral nectaries may also protect the plant – or specifically, the plant’s blooms – from the ants themselves. Ants are none too gentle with flowers when they’re looking for food, and because they’re very poor pollinators, there’s little incentive for plants to make their blooms attractive to ants. With rich, abundant nectar available at the extrafloral nectaries, the ants are much less inclined to forage the more delicate blooms for food. In a sense, the nectaries are acting as decoys.

There’s another theory that’s been used to further explain the purpose of extrafloral nectaries: the nectaries attract enough ants to set up an actual ant colony close to the plant, and the waste created by the colony enriches the soil around the plant. This theory sounds reasonable enough, but I’m reserving judgment on it. I’ve seen too many roots destroyed by nearby ant colonies to believe that enriching the soil offsets the root damage caused by ants. Indeed, one of my petunia patches was destroyed by a particularly voracious ant colony just last year!

No Ants Necessary

The idea that ants are necessary to open peony flowers is, in fact, a myth; peony flowers open when they have reached the blooming stage, regardless of the presence or absence of ants. (In fact, we have hundreds of peonies blooming in the greenhouse right now, all without the aid of any insects.) Yet peonies do indeed have a beneficial relationship with ants; no matter how much some of us dislike ants crawling over our plants, it’s obvious that both the insects and the plants benefit from this symbiosis. I guess people aren’t the only creatures guilty of succumbing to a sweet tooth

First Published 4/21/2005
Tree Sites

Last fall, I was listening to a lecture by world-renowned tree expert and professor of forestry at the University of Georgia, Dr. Kim Coder. He said something that was incredibly wise, and yet remarkably simple, with a touch of that down-home common sense. He looked straight at the huge group of arborists and said, “Crappy site, crappy tree.”

Words of Wisdom

Those four words, though crude, should be gospel for anyone who’s going to plant a tree this spring. Too many people buy trees, stick them in any old piece of ground, and exonerate themselves from any further responsibility. It’s as if they’re thinking, “Okay, tree, I’ve done my job – now you do yours!”

The problem is, a tree can’t pack up and move to a better spot, nor can it dig itself a better planting hole, amend poor soil, or ignore the effects of concrete pads, or even overhead power lines, let alone all the other obstacles that a poorly-chosen planting site presents. It will try to adapt to whatever environment the gardener presents it with, expending precious energy just trying to survive – energy that could be devoted to healthy growth. You can’t expect a young tree to reach its full potential when it’s burning up all its precious reserve energy as its roots try, unsuccessfully, to penetrate heavy clay and rock.

It’s not just homeowners that are guilty of plunking down trees in crappy sites. I’ve seen countless examples of commercial plantings in cities that often defy logic. Some of the worst examples include sun-loving trees planted right up against high-rise condominiums, shaded on one side by the enormous building and on the other by rows of huge street trees. All plants need sunlight, and trees in this situation are destined to lead a short, unhappy life. Oh, they’ll hang on tenaciously for a few years, but eventually they’ll be headed for the chipper.

The Right Site

This unhappy fate can be avoided if you devote just a little extra time and energy to choosing the right planting site and preparing it properly for your new tree. A happy site is three dimensional; imagine a “planting sphere” that encompasses the length, width and height of the mature tree’s trunk, branches and root system. Look upwards for potential obstacles such as power lines, eaves troughs and neighbouring houses. Then turn your attention downwards, to the soil, and ensure that it’s top quality: ideally, rich, deep, black loam. If you don’t have that soil to start with, then make amendments!

Avoid locations buried in deep shade, set in boggy, swampy spots, or where the soils have been compacted into airless concrete by heavy equipment. And of course, you should follow the advice of the utility companies and “dial before you dig” to avoid buried power and sewer lines.

Above all, know the mature height and spread of the tree; this information should be on the tree’s tag, or at least the nurseryman should be able to tell you the tree’s mature dimensions. And keep in mind that the tree’s root system is more extensive than you might think; it typically grows far beyond the diameter of the tree’s canopy.

Pause for Reflection

Choosing a good site for your tree is largely a matter of common sense. Good soil, the right quantity of moisture, sufficient physical space for the entire mature tree and plenty of sunlight is the basic recipe for success with all trees. So when you bring that promising young tree home from the nursery, don’t be in a huge rush to get it into the ground; rest your chin on that long-handled spade, take a look around, and really think about the planting site. Even better, chose the best site in your yard first, and then decide what kind of tree is best suited to the spot. A few minutes’ sober consideration on planting day can save you hours of headaches in the years to come. Just as a crappy site leads to a crappy tree, a happy site gives you a much better chance of a happy tree – and a happy gardener.

First Published 4/14/2005
Internodal Spacing

If you’re sheltering transplants in your home or hobby greenhouse until you feel the weather is good enough to move them outside, you’re probably familiar with internodal spacing. Well, you may not know the phenomenon by that particular name, but the concept is familiar enough: internodal spacing simply refers to the amount of stem space between a plant’s branches. When there’s too much internodal space, we call the plants “stretched.” To the untrained eye, the amount of space between branches may not seem terribly relevant. But stretching – or to be more scientific about it, the presence of excessively wide internodes – can have grave consequences for your plants once they are moved outdoors.

A Space Oddity

Plants develop wide internodal spaces whenever they’re grown in conditions that are less than ideal. For example, take a look at a young tomato transplant, just a few weeks away from being transplanted into the garden. I like to keep the internodal spacing on tomatoes down to about five centimetres on young transplants, but I’ve seen many plants that have internodal spacing of twelve centimetres or more. Internodal gaps this large are a clear sign that the plants will be too tall, floppy and soft to adapt to the outdoor environment. When I see tomato transplants that are this stretched and lanky, I can virtually guarantee that they were grown too warm and too wet. In the garden, these gangly plants will almost certainly flop over, because their tissues are simply far too soft and weak to stand up to the stresses of intense sunlight and strong winds. Bronze-coloured patches of dead tissue on stems and leaves are the inevitable result. And of course, this damage makes the plants much more prone to attack by diseases and insects. Some soft, stretched plants do indeed recover, but a large percentage of them will require replacement.

Putting the Brakes on Stretching

One very effective technique that is used in commercial greenhouses to control this internodal stretching is called “DIF.” DIF is a just a contraction of the word “difference,” and refers to the difference between day and night temperatures in the greenhouse. One wouldn’t think that this temperature difference would have much of an effect on stretching, but manipulating day and night temperatures can have a profound effect on internodal spacing.

There are three DIF strategies: positive DIF, where the day temperatures are warmer than the night temperatures, negative DIF, where the day temperatures are cooler than the night temperatures, and zero DIF, where the day and night temperatures are the same.

For the vast majority of transplants, growers apply negative DIF – that is, they set their heaters for warm nights and cool days. A strong negative DIF shortens internodal spacing and leads to stocky, robust growth, while a strong positive DIF (cool nights, warm days) causes the opposite effect; the plants stretch out and grow lanky and weak.

As the difference between daytime and nighttime temperatures widens – that is, as the negative DIF increases – the internodes become shorter. For example, temperatures of 22 degrees C at night and 20 degrees C during the day will produce plants with longer internodal spacing than at nighttime temperatures of 22 degrees C and daytime temperatures of 16 degrees C.

In the home, arranging negative DIF is a challenge. You can approximate it, though, by finding a cool but bright spot in the home or on the deck (weather permitting) and a warmer spot at night. You may not be able to achieve very precise control over the temperatures in your home, but every little bit of negative DIF will help your seedlings grow thicker and stockier.

Making a DIFference

Of course, DIF isn’t the be-all and end-all of growing transplants that will survive the transition to the outdoor garden. Choosing the best seed and plant varieties is always the best start, followed by proper watering and feeding, and choosing the right location. But paying a little attention to internodal spacing, and using DIF to keep those spaces small, will help your transplants make the outdoor trek a little less perilous.

First Published 4/7/2005
Pruning Raspberries

Right around now, raspberry patches often look a little haggard. Many canes (the correct term for raspberry branches) are bowed over from the weight of the past winter’s snow, while others are completely dried out, their stems split open. Might this be a good time to oil up the old pruners for a little rejuvenation work? Or can you leave well enough alone?

The Cane Mutiny

To be honest, pruning your raspberry bushes isn’t essential; raspberries are tough and will continue to grow whether you prune or not. However, if you choose not to prune, the canes will eventually grow exceedingly dense; dead canes will be mixed with live ones. This overcrowding leads to lower fruit yields and poorer quality fruit. Also, the canes and fruit will become more vulnerable to pest and disease attacks.

So you can choose one of two paths: one leading to high yields and beautiful shrubs, the other leading to an impervious mass of poorer-yielding canes. I say, no pain, no gain – get out those pruners!

Raspberry Pruning Technique

To prune raspberries properly, it’s necessary to understand a little about their biology. Most raspberry varieties grown across the country have a biennial fruiting habit; in other words, a raspberry bush will produce a shoot in the first growing season that develops a lot of leaves, but no fruit. These shoots are referred to as primocanes. During the second growing season, the primocanes will produce flowers, becoming floricanes. The flowers will produce fruit later that same season, and the floricanes will then die, to be replaced the following season by a new set of primocanes.

This growth pattern makes pruning raspberries refreshingly straightforward: once you’ve harvested the fruit from a floricane, simply cut it off at ground level, which will open up space for the new primocanes to thrive. If you haven’t been pruning your patch regularly, you’ll probably notice that many of the floricanes look old and dry; these should be cleaned out before the surrounding canes leaf out.

Still, even if you remove the dead floricanes now and the remainder after they fruit in the summer, you can still wind up with an exceedingly dense, unmanageable patch of raspberries. The trick is to think of your raspberries not as a patch, but rather as a hedgerow. Commercial growers tend to grow raspberries in rows that are perhaps 40 or 50 cm wide, with the rows spaced three metres apart. (Some growers like to make the rows 90-120 cm wide, and space them two metres apart; depending on how much space you have, both are viable options.) Growing in hedgerows allows for excellent light penetration into the foliage, good air movement, easier access for bee pollination (essential for good fruit production), and easy access to the berries at harvest time.

Even if you haven’t planted your raspberry bushes in nice even rows (or if you only have one plant), you can still achieve the same effect by pruning out floricanes after they’ve borne fruit, thinning out some primocanes (leaving about six primocanes per 30 cm of row), and trimming of suckers to keep the raspberries contained.

There are relatively new varieties of raspberries, such as ‘Red River’, that bear fruit on primocanes – in other words, on the current season’s growth. Pruning these varieties is incredibly easy; you just have to cut all the canes down to 30 cm tall after the harvest. But keep in mind that these varieties bear fruit a little later in the season than standard, biennial-fruiting varieties.

Prune with Prudence

You don’t have to prune now if you don’t feel like it; if you want, you can put off the job until fall. But whenever you choose to prune, be sure to wear heavy duty protection when you venture into the raspberry patch; the masses of prickly thorns that cover the canes can shred hands and forearms in pretty short order. The aphorism “death of a thousand cuts” may not have been coined by someone who journeyed sleeveless into a raspberry patch, but the metaphor certainly applies here.