First Published 11/27/2003
The Point of Poinsettias

What’s the point of poinsettias? Some would argue that poinsettias are the work of the divine, custom-designed by a benevolent supernatural force for our Christmas pleasure. Well, that may sound like a good theory, but if the poinsettia could choose its own destiny, it might just as soon spend its time with hummingbirds.

In the wild (i.e., the regions of Central America and Mexico where poinsettias are indigenous), hummingbirds feed on poinsettias, drawing sugar-rich nectar from the flowers while at the same time inadvertently spreading poinsettia pollen from plant to plant. This dispersal of pollen among poinsettias spreads each individual plant’s genes far and wide, ensuring that there will be future generations of poinsettias.

A Natural Ad Campaign

However, before hummingbirds will deign to visit poinsettias, the plants must undertake a splashy advertising campaign. Poinsettia flowers are rather inconspicuous; they’re tiny yellow structures at the centre of the plant, which hummingbirds would be unlikely to find without the help of the poinsettia’s most attractive feature, the bright, showy, usually red, modified leaves we call bracts. Sometimes mistaken for flowers by human beings, the bracts act as huge billboards to hummingbirds, drawing them to the flower’s tiny yellow centre like an arrow to the bull’s-eye.

The poinsettia’s advertising strategy works because hummingbirds, like all birds, have a keen colour sense, not that far removed from our own. So it’s not surprising that most bird-pollinated flowers are red or yellow, colours that are bright and easy to spot against a typically green background. Also, since birds don’t have much of a sense of smell, most bird-pollinated flowers, the poinsettia included, have little fragrance.

This lack of fragrance is, in fact, a form of negative advertising for certain insects, such as beetles. Since poinsettias lack a strong scent, most beetles aren’t tempted to visit. Nor are they attracted to red bracts. (Some butterflies are attracted to red bracts, and likely play a minor role in spreading poinsettia pollen.) Poinsettias are nectar-rich plants, and if beetles were ever to visit them, they’d find enough food on a single poinsettia flower to satisfy all their nutritional requirements-enough nectar, in fact, to keep them from wandering to other poinsettias. In a scenario like this, there’s no payback for the plant; the genetic material in the pollen never gets transferred to other poinsettias. Nature hates freeloaders, so it’s no wonder that poinsettias don’t design their advertising campaign for bugs!

Points of a Different Colour

If poinsettias depend upon their bright red bracts to attract hummingbirds, one might ask why white poinsettias exist. Well, there’s another warm-blooded animal that has an affinity for poinsettias: humans. Sometimes poinsettias will spontaneously mutate and produce pigment-deficient bracts. Normally, this would spell certain doom, reproductively speaking, since hummingbirds tend to ignore white bracts. But even if they do spread the white poinsettia’s pollen, this mutation is carried in the shoots, not the pollen, so future poinsettias would likely be their normal red, even if pollinated from a white poinsettia.

However, since people have taken quite a liking to white poinsettias, this aberrant trait is likely to persist for some time to come; breeders actually seek out such mutations so that they can be preserved and propagated via cuttings. In a sense, poinsettias can’t lose: even if they mutate, some star-struck human being might just step into the hummingbird’s role and play midwife.

The Real Point

From the poinsettia’s perspective, the real point of red bracts is simply to reproduce. To that end, poinsettias have done a wonderful job of establishing mutually beneficial relationships with two very different species: hummingbirds, who depend on the poinsettia for food, and humans, who have grown to depend upon the poinsettia’s beauty during the holidays. Even though poinsettias don’t consciously produce those gorgeous red bracts for our benefit, you can’t help but appreciate these beautiful, if self-centred, plants.

First Published 11/25/2004
The Phosphorus Placebo

Fertilizer has become the great panacea of the plant world; in particular, many gardeners have been led to believe that applying phosphorus-rich fertilizers is the best way to encourage flowering. Indeed, the link between flowering, fruiting, rooting and phosphorus is so pervasive that it’s widely held as gospel truth. You’d be hard-pressed to find a gardening book that doesn’t say that phosphorus causes plants to flower. There’s only one problem: it isn’t true.

Phosphorus Findings

It wasn’t until fairly recently that horticultural researchers cast doubt on the link between phosphorus and flower and root growth. Not only did they discover that high phosphorus fertilizers had no effect on flowering, they also found that plants continued to flower even when soil phosphorus was extremely low.

In the greenhouse, I’ve tested low phosphorus feeding regimes on hundreds of varieties of annuals and perennials, and my anecdotal evidence supports the findings of these researchers. Even with extraordinarily low levels of phosphorus, I found no reduction in flower numbers, and rooting was just as prolific as it was in high phosphate soil.

This being the case, why bother with phosphorus fertilizers at all? While high levels of phosphorus have little effect on rooting and flowering, plants still need it. A plant growing in soil with hardly any phosphorus will remain stunted. Phosphorus is an integral factor in the energy system of every plant (and every person, for that matter); it helps transform raw sunlight energy into a form the plant can use for its various life functions. A plant without phosphorus is like a car loaded with fuel, but no engine to burn it. Phosphorus is definitely vital – there’s a reason it’s the second number on every fertilizer label – but it’s never the direct cause of flowering.

Flower Factors

If high levels of phosphorus aren’t essential for flowering and fruiting, then what is? Unfortunately, there’s no single factor or ingredient that’s guaranteed to cure every species of plant that has never flowered or has quit flowering. Usually it’s a light deficiency that’s causing the problem, particularly with indoor plants during the winter; at this time of year, plants simply have a tough time gathering all the light energy they need to produce flowers. And there are other factors at play: some plants need long days to flower (petunias), short days (poinsettias), cool nights (osteospermum), or even a minimum number of leaves (clivia). If you want your indoor plants to flower, the best advice I can give is to place them next to the sunniest window in the house, keep them well-watered, and hope for the best. The return of long, sunny spring days is often all the impetus indoor plants need to initiate flowering; dumping heaps of fertilizer into the pot isn’t going to make a lick of difference.

Whither Phosphorus?

I wouldn’t feel too badly if you’ve used phosphorus as a mainstay of your gardening routine; it is an essential plant nutrient, after all. But it is time to drop the myth associating phosphorus and flowering. If you want plenty of blooms, start with the right variety, plant it in good soil in the right location, and provide consistent water and judicious amounts of fertilizer. There’s no magic pill when it comes to flowering; those kinds of miracles are best confined to late-night infomercials. In the real world, a more diligent approach is required.

First Published 11/18/2004
For the Love of Latex

Latex has become an integral part of our lives; it’s used for everything from surgical gloves to prophylactics to counter-culture fashion. And while latex may look and feel like something artificial, it’s actually as natural and as close as the poinsettia on your table.

Sap is Thicker Than Water

Plants that exude a white, sticky sap – latex – are typically, though not exclusively, from the Euphorbiaceae family. Both the fig tree and rubber tree in my house are members of this family; I think of them as “bleeders,” because every time I prune them and forget to put a towel down, I wind up with blotches of latex all over the floor. Poinsettias produce latex as well, but they don’t bleed nearly as profusely as rubber trees. (Though they will bleed whenever their foliage is broken, and as poinsettia latex dries, it turns an ugly brown colour; growers refer to this material as “crud.”)

Latex producing plants have structures within their tissues called lactifers, which are, essentially, latex storage vessels that bleed when broken. Latex is likely a defence material that seals cuts and gives certain insects a mouthful of distasteful liquid. The latex produced by plants such as fig trees and poinsettias is not that different than the latex produced by the heavyweight of the Euphorbiaceae family, the source of commercial rubber, the rubber tree (Hevea brasiliensis). In fact, many different plants have been investigated as potential alternatives to the rubber tree, though the yield and quality of rubber tree latex remains superior to that of all other latex-producing plants. But poorer-quality latex has worked in a pinch; the Russians used the dandelion as an emergency source of latex during World War II.

Rubbery Bonds

Latex contains a multitude of chemicals, but the one that’s essential for rubber production is called isoprene. Isoprene molecules are small, but when they bond chemically, they form vast strings that hook together in much the same way as the plastic monkeys from the old “Barrel of Monkeys” kid’s game. Long strings of isoprenes are called polymers, and their bonds are arranged in such a way that they can stretch and rebound to their original shape.

But even these strings of isoprenes require one more key ingredient to yield the high quality rubber we depend upon for gloves, tires, and thousands of other products: sulphur. The addition of sulphur to latex to form rubber is called vulcanization, and depending on the percentage of rubber added, the process can create very stretchy products like rubber bands (low sulphur content) or hard rubber items like car tires (high sulphur content).

Tickled by Chicle

There are some “almost rubber” products derived from the latex of the sapodilla tree (Achras sapota). This latex, also known as chicle, was chewed by the Mayans and was once seen as a potential substitute for rubber latex. Unfortunately, the somewhat random connections of its chemical bonds made it unacceptable for conversion to a rubber-like compound. Nonetheless, we still benefit from the discovery of chicle; it’s commonly enjoyed in chewing gum form as the aptly-named Chiclets.

The Big Bounce

As annoying as latex can be when you’re pruning your favourite rubber tree or pinching a poinsettia, we owe a great deal of gratitude to these plants. For every drop of latex they shed, humanity has enjoyed a multitude of benefits.

First Published 11/11/2004
Ancient Soil

I love the science of soil, so a couple of weeks ago I jumped at the opportunity to attend the Bentley Lecture in Sustainable Agriculture at the University of Alberta. Soil researcher Dr. Phil Brookes was the guest speaker, and his lecture revolved around the oldest agricultural research station in the world, located in Rothamsted, England. Field experiments have been going on there for more than 160 years, so I figured that there would be a lesson or two from those venerable plots that could be applied to our own gardens.

The Rothamsted Plots

One of the earliest experiments conducted at Rothamsted was to prove whether or not fertilizers had any effect on crop yield. Originally, the thought was that only manures increased crop yield, thanks to the absorption of carbon from the manure. (Of course, we now know that carbon is absorbed only from the air, not the soil or any supplements.) A researcher named J.B. Lowe hypothesized that inorganic nitrogen, phosphorus, and potassium were as good as manure at increasing yield. The experimental results in Rothamsted not only proved him right – the proof made him a small fortune. Understanding the tremendous potential benefits of long-term agricultural research, Lowe reinvested much of his newfound wealth back into the Rothamsted plots, a gift that has helped the research continue to this day.

Dr. Brookes explained how critical long-term studies are to our understanding of how crop plants grow and the environment in general. Over 200,000 soil samples have been carefully collected and stored over the many years since the Rothamsted plots’ inauguration, and they continue to yield important and interesting data. For example, spikes in soil radionuclides (radioactive particles) coincide with the era of above-ground nuclear testing and nuclear disasters like Chernobyl.

Science in the Long Run

Dr. Brookes emphasized that often much of our research and thinking tends to be short-term; we consider years and decades at best, rather than centuries. Our reluctance to think in longer terms can produce misleading results. One experiment at Rothamsted seemed to show that crop yields increased during a period when atmospheric carbon dioxide levels were rising. Extra carbon dioxide means extra fuel to convert into sugars, and therefore more vegetative growth.

Well, the data may have been correct, but the conclusion was wrong – the researchers looked at their decades of accumulated data and used that information to determine that the investigation into the effects of atmospheric C02 coincided with the use of a new harvesting machine on the Rothamsted plots– a machine that cut foliage significantly lower than their old harvester. The increased biomass harvested wasn’t due to increased atmospheric carbon dioxide; the culprit was a more efficient cutting tool. Without the data of decades past, the true cause of the extra biomass would have been much harder to determine.

Dr. Brookes wasn’t implying that increased atmospheric carbon dioxide wasn’t a problem – rather, he noted that looking at the trend over a couple of centuries rather than a couple of decades allows one to obtain more data, and leads to a far better chance of a correct hypothesis.

The Breton Plots

In Alberta, we have one plot that mirrors Rothamsted: the Breton Plots, located about 100 km southwest of Edmonton. Since 1929, scientists have conducted agronomic work similar to that at Rothamsted, thanks to the foresight of some early researchers and the politicians who had the wisdom to approve the project. The knowledge gleaned from the Breton Plots over the years (for example, how important sulphur is to increasing yields in the grey-wooded soils of northern Canada) has been invaluable to Prairie farmers – and the lessons learned on the farm always trickle down to the home garden.

Temporary Caretakers

When you move into a home in an older neighbourhood, it’s easy to forget that there were likely quite a few people tending to the garden before your arrival. And since no one is immortal, there will be a long list of folks caring for what was once your garden after you’re gone. No matter how you look at it, you’re only renting the garden for a little while. Nonetheless, your impact on the garden can be felt for years down the line – and so can your experience, if you pass it on to your children or friends. Individual researchers – including gardeners – may not tend to their plots for long in the grand scheme of things, but the priceless knowledge they discover can last forever.

First Published 11/4/2004
Corn Gluten

A small zip-lock bag came across my desk the other day, filled with yellowy-orange granules. When I poured the stuff into my hand, it felt like crushed corn flakes and even had the aroma of cornflakes. A look at the spec sheet that accompanied this stuff revealed that it was not a bag of the popular breakfast cereal – but it was corn-based. The product was corn gluten, a fancy name for corn protein that’s being touted as the next big organic fertilizer and lawn weed killer

An Organic Option?

The fertilizer analysis of the corn gluten is 10-0-0, meaning that it contains ten percent nitrogen by weight, but contains no phosphorus or potassium. Nitrogen is one of the essential nutrients for maintaining a healthy green lawn. Under the Fertilizers Act administered by the Canadian Food Inspection Agency, fertilizer manufacturers must provide an accurate analysis of the three essential nutrients – N, P, and K – on the label, so although I haven’t tried this particular product, I would expect that with 10 percent nitrogen, this product will do a reasonably good job of supplying nitrogen to your grass.

However, the other claim – that corn gluten will kill weeds – requires a little further investigation. Corn gluten does have an interesting history. It’s a byproduct of the corn milling process, and its weed killing ability was discovered accidentally. Researchers used it as a substrate (growth medium) to grow cultures of pythium, a serious fungal disease of golf greens. The corn meal/pythium mixture was incorporated into the soil prior to sowing the golf green grass; the objective was to infect the green so the researchers could investigate ways of controlling the disease. But a rather strange thing happened: the grass failed to germinate. It wasn’t due to the disease, which, as luck would have it, failed to establish, but rather by something else in the corn meal. After much research, a protein fragment called alaninyl-alanine was isolated from the corn meal; it proved to be the primary growth-inhibiting compound in the meal.

Alaninyl-alanine is remarkably similar to trifluralin, a common agricultural herbicide. Both compounds inhibit cell division in root cells. In other words, seedlings treated by corn gluten develop stunted roots that are unable to absorb moisture and nutrients easily, resulting in the death of the seedling. They are also pre-emergent herbicides, meaning that they must be absorbed by the seedlings very shortly after germination to be effective. (This means that the corn gluten won’t harm established grass.)

Now, before you run out and buy a bag of corn gluten, note that the label states that the gluten kills germinating crabgrass and dandelion seedlings. Unfortunately – or fortunately, really – crabgrass is a pest of eastern Canada that doesn’t survive Prairie winters. Our worst lawn pest is quackgrass (often confused with crabgrass), but since quackgrass spreads primarily via rhizomes (shoots) rather than seeds, corn gluten is not an effective control. Secondly, established dandelions are unaffected by corn gluten; while any germinating dandelion seedlings will be suppressed by the gluten, established dandelions will escape the treatment unscathed. On the positive side, growth of seedling dandelions will be inhibited when corn gluten is applied. Also, if you are trying to thicken your lawn by scattering some grass seed over it, remember that the corn gluten will likely reduce the percentage of the grass seed that germinates.

Finally, don’t be tempted to apply corn gluten to your vegetable garden to eliminate weeds. Corn gluten affects a wide range of seedlings, and can’t distinguish between your prized vegetable seeds and problematic weed seeds. (There may be some potential for corn gluten to be used as a herbicide around vegetable transplants, but it’s not registered for that use yet, so be forewarned: it’s a bit of a gamble.) If you apply corn gluten to your vegetable beds, don’t expect a bumper crop!

Have a Backup

Since this protein is a naturally occurring component of corn meal – found commonly in products like corn flakes – it didn’t have to jump through as many regulatory hoops as chemical pesticides do before being approved as a herbicide. So you may want to give corn gluten a try, but I wouldn’t anticipate the extinction of dandelions anytime soon.