First Published 7/28/2005
Salts of the Earth

Legend has it that after the Romans defeated Carthage in the Punic Wars, they sowed salt into the soil around the fallen city, so that the Carthaginians would never rise again. Fortunately, our gardens will likely never have to face a disaster of that magnitude, but soil salt can still be a problem on a smaller scale.

Defining Salt

When we think of salt, there is a natural tendency to imagine only the stuff we sprinkle on food: plain old table salt, AKA sodium chloride. And while this most recognizable of salts can indeed be found in both Prairie soils and potting soils, they are often outnumbered by other salts. (Australia is a notable exception, where soil salts are largely comprised of NaCl.)

To put it simply, salts are ionic, a fancy way of saying that they’re composed of charged particles, either positive or negative. Nitrates and sulphates, as well as ionic calcium and magnesium, are all salts found in garden and potting soils, and are essential plant nutrients.

Some salts are relatively insoluble in soil, while others are highly soluble, and it is these soluble salts that contribute to high salt levels in the soil.

The Soil Test

Salts, then, are natural components of soil and can be very beneficial – but as we all know there can be too much of a good thing. The other week, I received a soil sample from a company that was planning on filling an enormous concrete planter with loam, and they wanted it tested to be certain that they were getting a quality product. A quick visual check indicated that the soil sample was rich in organic matter, and it had an excellent loose texture that was ideal for root growth. But looks can be deceiving, so as usual I sent the soil off to the lab for a chemical analysis called an E.C. test to ensure that it was suitable for healthy plant growth.

An E.C. (electrical conductivity) test determines just how many soluble salts exist in a given quantity of soil; the measurement is taken with a device called a conductivity meter. The greater the electrical current that passes between the two electrodes on the meter, the greater the concentration of soluble salts in the soil.

Shocking Results

In this particular sample, the soluble salts were a whopping four times higher than what should be in a good quality garden soil. At levels this high, water moves out of the plant’s roots and into the salty soil, rather than the other way around. And while it’s tempting to think that you’re getting a bigger bang for the buck with the extra nutrients, your plants don’t see it the same way. Just as humans are unable to hydrate their bodies by drinking seawater, plants encounter the same hydration problem with salty soil.

When a plant is grown in a high E.C. soil, it will look like it hasn’t been watered in weeks, even if that soil has been kept wet. This phenomenon is commonly called “burning,” because the plant leaves look singed on the margins.

Salty soils are becoming all too common thanks to the widespread practice of adding excessive amounts of manure into commercial soil blends. It’s not that manures are bad – just the opposite is true. Manure can add valuable organic matter and nutrients to any soil mix, but the key is moderation. Some species of plants, such as petunias, alyssum and beets, can tolerate moderate to high salt levels, while others, such as beans, squash, begonias and impatiens are very sensitive. (Some plants, known as halophytes, are extremely tolerant of salty soil; Distichlis stricta, also known as saltgrass, is a good example of a Prairie halophyte.)

Salty Solution

If you fear that you may have a salt problem with your soil, you’ll need an E.C. test to find out for sure. Some garden centres have the equipment to perform the test, for a fairly nominal fee. For home gardeners, the best way to avoid burning plant roots with excess salts is to be cautious when adding manure. But if you’re already saddled with very salty soil, the only practical solution is to soak it with water to leach (move) the salts deep into the earth, out of the reach of roots. Heavy rainfall will help, and be sure not to add any more manure or fertilizer to your soil until soil-soluble salt concentrations drop into a safe range.

Salts are absolutely essential for the health of your plants, but a little goes a long way. Keep the salt levels in your soil balanced, and you won’t wind up feeling like the defeated Carthaginians.

First Published 7/21/2005
Putrefied Peppers

Imagine that it’s August, and you’re just about to enjoy a big, juicy, bell pepper. The fruit is firm and unblemished, you slice into it, and…you find a rash of mold growing all over the interior of the fruit. After the initial shock, you’ll probably have three questions: what is that horrible looking stuff? How did it get through the skin of an otherwise perfect fruit? And is it safe to eat?

Invisible Invaders

At the Plant Canada 2005 conference held at the University of Alberta back in June, I attended a lecture entirely dedicated to this strange phenomenon. Researchers with Alberta Agriculture at the Crop Diversification Centre South in Brooks have spent a fair bit of time and effort investigating this pernicious pepper problem.

According to Alberta Agriculture, a genus of fungus called Fusarium produces the moldy growth; actually, there are four or five species within the genus that cause the decay of seeds and interior walls of pepper fruit. Two species in particular, Fusarium solani and Fusarium proliferatum, are by far the worst culprits in Prairie greenhouses and gardens. These fungi species consider the interior of pepper fruits a very hospitable environment for growth and reproduction, and no wonder; the pepper’s flesh provides plenty of food and water, and the fruit shelters the fungus from the effects of sunlight. From the fungus’ point of view, it’s a near-perfect home.

How the fungi take up residence in peppers is still the subject of some debate among scientists, but one current theory suggests that the fungi gain entry while the pepper plant is flowering. Fusarium spores drift onto the flowers (the theory even suggests that the spores may be carried along inadvertently by bees as they pollinate the blooms!) and then simply wait for the pepper fruit to grow and envelop them. When the interior environment of the fruit matches the fungi’s needs, the spores germinate and proliferate through the fruit. From the outside, the fruit looks perfectly healthy, but in reality, it’s rotten to the core.

And therein lies the problem for gardeners and professional growers alike. It’s tough to design effective control strategies for this pest when you don’t even know that your peppers are being attacked.

Do Not Eat

The mold caused by Fusarium isn’t just unsightly – it can also produce mycotoxins. Mycotoxins are poisonous byproducts of fungal growth that could be of concern to human health, if one were to consume enough of it. If you find a pepper infested with Fusarium mold, follow your likely first instinct: throw it away.

The Case of the Putrefied Pepper – Solved?

So far, interior fruit decay of peppers has been more of a concern for greenhouse growers than home gardeners. The higher temperatures and high humidity levels found in greenhouses are more conducive to fungal growth than the cooler, drier conditions found in gardens.

Discovering the cause of this extremely puzzling plant disease was a revelation to me, because I’ve encountered the disease several times, always wondering how the heck this disease got into the fruit. I can’t think of a worse disease from the perspective of a professional grower: one that you can’t detect until it’s far too late. But thanks to the researchers like those found at Alberta Agriculture, we are pretty close to understanding this particular affliction – and that’s the first step to finding a way to prevent it.

First Published 7/14/2005
Birch vs. Grass

A couple of weeks ago, I attended a lecture by Scott Wilson, Assistant Dean of Research at the University of Regina. He likened trees and grasses to icebergs – a strange comparison, until you realize that a huge amount of a plant’s mass lies below the soil surface, hidden from human eyes. What goes on beneath the surface has a huge impact on the health of your plants – especially when it comes to the competition for water and nutrients between grasses and drought-prone trees such as birches.

What Lies Beneath

Conventional biology textbooks typically show plants with a tremendous amount of above-ground growth with relatively miniscule root growth, but this is an anthropocentric viewpoint; because human beings can readily see nearly all of the above-ground growth but very little of the subterranean growth, we tend to assume that the vast majority of the biomass of plants is out where the sun shines.

But as Doctor Wilson pointed out, the reality is that 80% of a tree’s biomass resides below the soil surface, while the biomass of a typical patch of grass is a whopping 92% underground!

Birch vs. Grass

While listening to the lecture, I couldn’t help but recall all the suffering birches that I’ve seen lately. Dr. Wilson’s insight that, due to their massive root systems, grasses are very efficient competitors, reminded me that the birches that have suffered the most are typically growing in bright, sunny yards with lawn grasses enveloping the root zone below the birch trees. Birches growing in spots with shaded root zones and considerably less grass do considerably better.

While trees seem like much larger plants on the surface, the subterranean biomass takes on great importance when you’re talking about competition for water and nutrients. In fact, if grass and a tree are growing in the same spot, with the grass growing right up to the trunk, it’s the grass roots that will be first to the buffet table when moisture and fertilizer are applied under the tree’s canopy. The grasses will do their level best to intercept and absorb whatever nutrients and water attempt to pass through their enormous root system, leaving substantially less of these valuable resources for any tree roots that lay below. During years when rainfall is plentiful, birch and grasses coexist rather well, but during successive years of drought, the grass wins out.

Drought tolerant trees such as American elms can cope with competition from grass, but drought sensitive species such as birch struggle. If you look at typical transpiration rates of trees, which measure how much water is lost through leaves and bark, birch ranks near the top. In other words, birches are not particularly adept at water conservation. So any additional competition for limited water resources puts a lot of strain on birch trees.

That’s not to say that lawns are killing the birches; birches have coexisted with lawn grass for many years. But if a birch tree is growing in poor soil and you add grass competition and successive years of drought, then the odds of birch dying or at least being irrevocably damaged increase drastically.

Tilting the Odds

If you have a birch tree that’s suffered drought-induced dieback growing in the middle of your lawn, you may be tempted to remove the grass beneath the tree. The birch, however, is unlikely to recover at this point. If, on the other hand, you want to start fresh with a new birch, then I would suggest preparing a broad disc of organic mulch around the new tree’s base. A mulch of pine bark just a few centimetres deep will help reduce soil water loss, and of course there won’t be any grass competing with the tree’s roots.

Of course, the best remedy for drought-stressed birches is timely rainfall. Failing that, we need to acknowledge that drought-sensitive trees such as birches may require some supplemental irrigation when Mother Nature has other priorities.

First Published 7/7/2005
Echinacea

Echinacea, also known as purple coneflower, is one of the stalwarts of the Prairies; it’s been popular in Canadian gardens for a long time. What I find particularly fascinating about this genus of plants is how closely plant breeders and scientists are working on it to unravel the secrets of both its beauty and its medicinal properties.

A Perennial Favourite

Echinacea has been given a lot of attention during the past decade or so, from a variety of sources. Gardeners love it for its toughness and ornamental value, plant breeders love to work with it because it responds very well to crossbreeding, and the health-conscious love it because of its purported benefits to the immune system.

Echinacea, or coneflower, is a member of the aster family, which encompasses a vast array of very showy plants. Coneflower is tough, bold and beautiful; the large flowers, composed of a bristly central cone surrounded by colourful florets, have given the plant another informal nickname, “King of the Daisies.” (Also, the name Echinacea is derived from the Greek echinos, meaning hedgehog.)

All species of echinacea have deep, fibrous roots. Although this feature makes echinacea quite hardy and drought tolerant, it performs best in rich, loamy, well-drained soils that are watered consistently. Four species are native to southern Saskatchewan and Manitoba, a testament to their ability to ensure extreme head, cold and drought.

New Coneflowers

There are new coneflower varieties popping up all over the place. The Chicago Botanic Gardens, in particular Dr. Jim Ault, have done a lot of work with echinacea. Some interesting varieties have emerged from this work, including an orange and gold purple variety – highly unusual for a plant commonly known as “purple coneflower.” It took Dr. Ault ninety-six crosses to produce his trademarked ‘ Orange Meadowbrite’ variety, indicating that orange and gold pigments reside deep within the genetic material of the Echinacea genus. It just takes a little breeding work to coax them into view.

Other varieties, such as the two-tiered, rose-pink coneflower called ‘Doubledecker’ are equally striking. Created by breeder Eugen Schleipfer, ‘Doppelganger’ (also known as ‘Double Walker’ or ‘Doubledecker’) looks like an ordinary coneflower, but for the extra ring of flowers around the top of the cone.

Medical Breakthroughs

Because of the purported health benefits of echinacea, there has been a lot of effort put into identifying the species that have the greatest concentrations of medicinal compounds. In mid-June I attended two lectures at the University of Alberta that focussed on the use of molecular markers to make it easier to identify Echinacea species – a very important development, because the different species, including Echinacea angustifolia and Echinacea purpurea, have substantially different phytochemical profiles. For example, a half-dozen or so compounds found in echinacea show activity against diseases such as the common cold, but the amount of these medicinal compounds that each species contains can vary not only between species, but within each species as well.

The Pace of Change

Echinacea’s continuous evolution is just one example of how the world of gardening is rapidly changing. Gardening may seem like a pretty staid activity on the surface, but with new varieties coming and going and new discoveries teaching us more about the biology of plants, I’d say that gardening is actually one of the fastest-paced hobbies around.