March 2010 – Page 3 – The Garden Professors™

You say tomato, I say phytochrome

Yesterday I got an interesting email about a new product – a Tomato Automator. Briefly, this square, red plastic disk slips around the stem of a tomato plant to suppress weeds and pests. Most intriguingly, we’re told that the color “triggers a natural plant protein that makes tomatoes mature faster and product more fruit.”

Given this is a red product, it’s likely that the protein referred to is phytochrome (literally, “plant pigment”). Phytochrome activity is maddeningly complicated to explain, so we’re going to keep this simple and refer (somewhat inaccurately) to “active” and “inactive” forms of phytochrome. The active form of phytochrome exists when red light is predominant and encourages leaf expansion, chlorophyll development, and other characteristic of plants growing in full sun. In contrast, the inactive form of phytochrome occurs when red light is reduced, either at night (when there’s no light) or in shaded conditions, where far-red light is predominant. (Far-red light occurs just outside our range of visual perception but is absorbed by phytochrome.)

From a practical standpoint, this means a plant can “tell” whether or not its light environment is limited: both red and blue light are absorbed by chlorophyll, so a low level of red light means poor photosynthetic conditions. Under such conditions, “inactive” phytochrome causes many plants to become etiolated (have abnormally long stems) in an attempt to outgrow the shade before it starves from lack of carbohydrate production. In addition, this photosynthetically-poor light environment can also increase fruit set by redirecting resources to seed production rather than foliage – perhaps a plant’s last effort to reproduce before it dies.

OK, now onto the useful application of this information. Several years ago researchers investigated that effect of different colored plastic mulches on tomato production. Again, to keep this simple we’ll just focus on the effect of red mulches. It’s pretty much agreed that red plastic mulch reflects both red and far-red light, increasing not only red light but paradoxically the relative levels of far-red light. Theoretically, this shift would cause tomatoes to put more resources into fruit production, and indeed some studies found this to be the case.

Unfortunately, the phenomenon is not consistent throughout repeated field studies. Some of the other confounding factors are soil temperature (warmer temperature = more growth), insect and disease pressure (both decrease tomato production and are variably influenced by mulch color), and the fact that ethylene production (the plant growth regulator responsible for fruit ripening) is not controlled by phytochrome at all.

So are Tomato Automators worth the trouble? Probably not, especially if you have many plants requiring many automators.

I’m Saving Myself for Pollination

Let’s take a very brief respite from the socio-religious implications of science, soil testing, and compost tea to ponder a more lighthearted topic. I need a bit of a morale-boost.

You: “O.K. Holly, Spring’s allegedly coming…how about a closer look at some wildflowers?”

Me: “Done!” (fingers snapping)

For a short time in March, forest floors across Eastern North America can be absolutely littered with a multitude of sparkling white flowers. This very cool little plant, Sanguinaria canadensis, is one of the first wildflowers to emerge in the spring and colonizes deciduous and mixed woodlands.

Flock of bloodroots, open for business at the fabulous Mt. Cuba Center.

A member of the Poppy family, Sanguinaria is a monotypic genus; that is, there’s only one species. Commonly known as Bloodroot – mostly. However, S. canadensis is also known as (and I quote): Bloodroot, Red Puccoon, King Root, Red Root, Red Indian Paint, Ochoon, Coonroot, Cornroot, Panson, Pauson, Snakebite, Sweet Slumber, Tetterwort. Large Leaved Sandwort, Large Leaved Bloodwort, plus whatever else Aunt Minnie “knowed it by”.

As one of the first wildflowers out of the ground, it’s still darn cold when the Bloodroot flower appears, and they’re quite protective of their private parts. The one leaf emerges at the same time and cups around the flower, helping to protect the fragile blossom from wind, rain, and snow. The petals also close up at night to save the pollen,since in most locations it’s so cold that few insects, save the occasional fly or beetle, are out and about. And as a last resort, they can just “do it themselves”, better described as self-pollination.

I have been pollinated! Victory is mine!

If you break off a stem or piece of the root, out will ooze a reddish-orange juice, hence the common name. It’s been prescribed for myriad conditions by Native Americans and herbal practitioners. One of the more interesting properties is that the sap is an escharotic – it kills tissue. Ironically, according to herbal lore, to draw love to you, wear or carry a piece of the rhizome. If attempting this bit of magic, maybe it’s best not carried in one’s pants pocket.

Art, Science, and Faith

First of all, who we are and what we do. All of the Garden Professors are in the business of the science of Horticulture. What’s Horticulture? The standard definition of Horticulture is the art and science of tending a garden. Horticulture is clearly more than science but science is the foundation and underpinning. For anyone that needs convincing that Horticulture is an art as much as a science I suggest the following exercise. Go to a major research university and wander through their Botany or Plant Biology greenhouses. Observe the plants. They look like crap. The people working there are on the cutting edge of plant science; they sequence genes, they elucidate biochemical pathways but they can’t grow a plant to save their lives. Now wander through the Horticulture greenhouse; plants are thriving, flowers are blooming. What’s the difference? The horticulturalists not only have the science, they have the art. There is no denying that art and intuition play a role in growing plants, especially in ornamental horticulture where we deal with hundreds of species and cultivars, each with its own subtleties and nuances. But as educators, especially public funded educators, how do we teach intuition? It’s very difficult. What we teach are principles developed through systematic scientific inquiry. How do we know there are 17 essential elements needed for plant growth? Repeated experiments over the years. And our knowledge continues to evolve based on the scientific method. I’m old enough that I learned 16 essential elements as an undergrad; the need for nickel by some plants had not yet been established. As extension educators our role is to disseminate science-based information. For some of us that phrase is even in our job description. We can try to impart our experience and intuition but it’s a difficult thing.

It can be especially difficult when we deal with alternative systems for which a long-term knowledge base may be lacking. Despite perceptions to the contrary, we are not apologists for the status quo. Overuse and misuse of pesticides and fertilizers are rampant, especially in ornamental horticulture. A lot of our current research and extension programming deals with reducing water and nutrient usage to reduce run-off and to reduce leaching. I spend a lot of time telling growers things they don’t really want to hear. How do we know growers are potentially impacting water resources? Because we and others have done the scientific research. We’ve set out plots, we’ve fertilized, we’ve sampled leachate, we’ve measured run-off. And we’ve conducted extension programs teaching growers that they can back off fertilization and irrigation rates without reducing crop growth.

Where we get concerned is that some assume or take on faith that because a nutrient source is ‘organic’ or ‘natural’ it’s automatically better or safer for the environment. Is the nitrate from Chilean nitrate less likely to cause blue baby syndrome then nitrate from ammonium nitrate? Dr. Corey Reams developed his principles as revealed to him through divine revelation. Unfortunately most of us are not blessed with such experiences. Instead we rely on systematic scientific investigation to develop knowledge that we share with our clients. Personally I do not believe that faith and science are mutually exclusive. Some of the most brilliant scientists I have met in my career have been people of deep and abiding faith. But we need to keep each in its context. Science is knowledge gained through systematic inquiry. Faith is a belief system. The central tenets of most Christian denominations are stated in the Nicene Creed which begins, “We believe in one God…” Note it doesn’t start “We know…” or “We can prove…” In their liturgy Catholics, “proclaim the mystery of faith; Christ has died, Christ is risen, Christ will come again.” Not only can they not prove these things they celebrate the fact that it’s a mystery. Faith does not demand proof. Science does.

Friday puzzle solved!

Lots of brainstorming over the weekend, and all the answers were legitimate. A few people came close with the observation that the roots looked like they had grown over something. And that’s exactly right:

This is a great example of nurse log decomposition. When the tree on the right first began growing (and it could have been decades ago), it sent lateral roots out, over, and around the nurse log to reach the soil. As the nurse log degraded, the tree’s roots were left high and dry, outlining the girth of the original log.

Does this natural example have application in managed landscapes? Absolutely! As several of you pointed out, removal of soil or organic matter by erosion or decomposition can leave woody roots exposed. If these roots are injured by feet or tools, they can lose their bark and become open to disease or pests. These are the structural roots of the tree, and if their stability is compromised, so is that of the tree.

(Though this tree has had some injury to its roots (probably from hikers), it’s unlikely to fail as it’s pretty small. )