The Role of Horticulture in Plant Conservation

Susan Wallace

Bok Tower Gardens,
P.O.Box 3810, Lake Wales, Florida, 33859-3810, U.S.A.


Abstract

Defining a role for horticulture in plant conservation has not been without some controversy. After all, the science of horticulture was developed to produce food crops and flower gardens. What useful contribution can that knowledge have in the preservation of rare and endangered wild plants?

The answer to that question is not what any of us expected when Bok Tower Garden's Endangered Plant Program began six years ago. Armed with the latest petunia-growing technology, we set out to reproduce some extremely rare plants. At first we probably succeeded more often with intuition than with science, but we have since developed an approach that is pragmatic, empirical, and results-oriented.

This ex situ program now addresses some 37 species, a few with considerable success. Case histories from the program will illustrate the progress and revisions in our thinking about what works horticulturally and what does not.

Now we can answer with more certainty: what can plant conservation learn from horticulture? What can horticulture learn from plant conservation? And what can we all learn from the plants themselves?


I would like to admit at the outset my personal bias - I am a horticulturist and I speak to you from that point of view. I would rather have my hands in the dirt than sit behind a desk. Nothing makes me happier than to grow plants.

Having said that, I am always astonished to realise how little non-horticulturists know about horticulture, both as a science and as an aesthetic. The origins of horticulture as a science stem from the production of food crops and the planting of gardens. And the traditional aesthetic has been the imposition of a manmade order on growing things. Many of the nonhorticulturists I know have been sceptical that horticulture - a flower-pot mentality - would have anything to offer plant conservation.

One prominent plant conservationist worried aloud to me that horticulture was some kind of evil plot threatening to ring our natural areas with clipped boxwood hedges and hybrid petunias. If that is something of an exaggeration, clearly he feared the manipulative, controlling aspect of horticulture, feared that horticulture would make natural areas into gardens, and turn rare plants into domesticated pets.

Another wellknown botanist asserted vehemently to me that wild plants grow only in the natural soil in which they are normally found and could not grow in a commercial soilless mix. Not only is this wrong, it reflects a commonly-expressed fear that horticulture will somehow change or corrupt helpless wild plants by doing unnatural things to them. And I have heard it said that plants grown in cultivation are not even the same plants as the ones growing in the wild. Comments like these, which still leave me wideeyed with wonder, make it clear that horticulture's role in plant conservation, indeed horticulture itself, must be more clearly defined and in the process perhaps redefined, both as a science and as an aesthetic.

If we consider plant conservation to be a multifaceted effort involving land preservation, land management, ex situ research, and the introduction or reintroduction of new populations, then the utility of horticulture becomes selfevident, even to the sceptics.

The circumstances of some endangered species are so precarious that they do not have a prayer of survival without the plantbyplant intervention of a horticulturist. Some species exist only on land that cannot be preserved, or in a habitat that is too severely degraded for them to persist much longer. And some hang on in numbers so few that they are especially vulnerable to stochastic events. It is in these cases that the term 'protective custody' has such emotional appeal. It also carries with it an awesome responsibility if our wellmeaning but imperfect skills cause more harm than good. Who among us has the courage to take cuttings off a plant with only a few sparse branches?

Botanic gardens have a long tradition of collecting and growing rare plants, more often - l suspect - for their curiosity value than their conservation value. The idea of systematically collecting, propagating, and maintaining large numbers of rare plants, representing a comprehensive genetic spectrum, is a relatively new idea, and one which presents a broader and more complex interface between plant conservation and horticulture, between the rare wild things and the imperfect science which seeks to preserve them.

Growing one plant in one pot is a certain, rather limited, challenge. To grow 200 plants for an indefinite period and maintain the genetic diversity among them is not the same challenge 200 times over. It is a quantitatively and qualitatively different challenge, and a far more difficult one.

What models are there for the role of horticulture in meeting this challenge? Really there are not any. I have been growing genetic collections of rare plants in a botanic garden for six years and I have been making it up as I went along. My horticultural skills have been successful with some species, and wholly inadequate with others. We have a special moral and ethical obligation to rare plants (more than we would have to common ones) and we must make the most conscientious use of the limited amount of plant material available. We cannot afford to be sloppy or thoughtless, but are obliged to use the best science and the best intuition we have available.

Where do we find the best horticulture today? From what I have seen I would say: not in botanic gardens. I am astonished at the antiquated and laborintensive practices I have seen at some of the world's most distinguished institutions, and I am amazed at how seldom the subject of horticultural standards ever comes up in botanic garden circles. I weep to tell you of the curator who proudly took me to see the last remaining cycad of its kind, deep in the shade of an old palm house, on a muddy floor, with only 3 fronds left on it.

Can we look to universities for good horticulture? Here I can speak only to what I know in the United States where horticultural research is funded largely by commercial interests. Research there centers on things like 'the effects of ethylene gas on philodendrons during shipping' or 'the physiology of light responses in poinsettias', but very little research on cultivating wild things.

Oddly enough, commercial horticulture offers us a lot to think about in our own work. I am not suggesting that we treat our rare wild things like petunias, or even that they would behave like petunias, but we can improve our horticultural methods and standards by thinking like a commercial grower.

First is the question of scale. If we are serious about preserving a species we should be thinking in much larger numbers - not a few plants in pots on a greenhouse bench. Depending on the life-span of the species and the amount of propagating material available, we should be propagating hundreds of plants. And for introduction projects, thousands of plants, acres of plants. To preserve the range of genetic diversity in a species, and to grow enough individuals to maintain the integrity of the collection over many generations, we should be using the best technology available to massproduce rare plants like a commercial crop.

What about the quality of the plants we produce: are they growing at a normal rate? Are they healthy with a strong root system? Using the same standards you would use for a rose bush in a garden center, ask yourself 'Would I buy that plant?' Actually, some of the rare plants I grow are so naturally ugly that no one would buy them, but I can ask myself, 'Does this plant look at least as good in the pot, or in the garden, as it does in nature?' If it does not, something is wrong with the horticultural techniques.

Finally, the really tough question: are we producing the plants with the speed, efficiency, and cost-effectiveness of a commercial grower? Here I am not suggesting that the rare plants should have to justify themselves in economic terms, but our horticultural methods should have to. We should be held accountable for using our resources - labor, equipment, and space - in the most efficient way. Ask yourself what a commercial grower has to ask: 'Could I make a profit selling this plant?'

If you did the same costaccounting that a commercial grower does and added together all the costs of your plant production operation (including the really big salaries that botanic garden employees make) and calculated what it costs to grow and maintain plants per square foot per year in your greenhouse and garden, you would have a whole new measure of each plant and of the quality of your work.

Are you horrified at the idea of assigning a dollar value to a rare plant? Think about it. Knowing how much it costs to produce and maintain the plant ex situ may be a very telling measure of your skills and efficiency. It may also be a very compelling argument for preserving the plant in situ.

I said that in defining horticulture's role in plant conservation, we might end up redefining horticulture itself. In that vein, I have some thoughts on what horticulture can learn from plant conservation and from the rare plants themselves.

I have learned more respect for individual variation. Yes, I know I talked about growing plants like crops, but to preserve the genetic variation in a population there must be some tolerance - even appreciation - of the differences among individuals.

As an example, the Conradina grandiflora in our collection (it is a woody mint which resembles the common herb rosemary) clearly demonstrates clonal differences even to the untrained eye. Looking at a bed of 50 clones, each one is distinct - some are compact bushes, others sprawl, one clone is determined to grow flat on the ground. Most look green but one turns its leaves upward flashing the white undersides giving the entire plant a silvery look. Most bloom with lavender flowers, some have dirty white blooms, and one is distinctly purple.

The old horticulturist in me would naturally have favored the most compact and floriferous clone and disdained the rest. Today the revised horticulturist in me celebrates these differences and the story they tell to our visitors about genetic diversity.

And I admit to an appreciation of natural growth forms and random patterns in the landscape and a less controlling aesthetic. The new form of horticulture which is emerging from the interface with plant conservation seeks more to assist nature than to dominate it, to restore wildness rather than to tame it.

When I used to teach nursery management, the final exam question asked students if and why plants grow better in straight rows. This was meant to be a discussion of the physiology of competition, but I am still intrigued with the philosophical implications. Do plants really grow better in straight rows? As we bring our best horticultural technology to bear on plant conservation projects, we ought to ask when it is time to leave off horticulture and let nature take over.

Finally, I would like to offer up some challenges. I would like to hurl these challenges into the audience and if they stick where they land. I invite you to the workshop which follows on horticultural standards in plant conservation.

What are the goals of a plant conservation program? I do not mean some broadlywordly glorified verbiage about saving rare plants, I mean what exactly do you plan to accomplish in the end? I would expect the goals to differ from garden to garden, but are they clearly defined? Are they really attainable? Are we certain that our limited resources are directed toward projects that will actually work? Are we designing projects that are the most efficient and effective ways to save rare plants? And the biggest hurdle of all: have your plants read the Botanic Gardens Conservation Strategy?

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