INTRODUCTION Thomas Jefferson wrote,"Though an old man, I am a young gardener." The longer I garden, the more I realize the truth of those words. Gardening never ceases to capture, recapture, and then recapture again my interest in a lifelong learning experience. How could it not, representing such a congenial confluence of colors, flavors, and aromas seasoned with the weather, whatever pests happen to stop by that season - and the science behind it all?! And the science behind it all what this book is about. It''s not a comprehensive overview of botany and related sciences, just some of the natural science that can be applied to a garden. Knowing some of the underlying science at work in the garden also makes for a more resilient gardener, better able to garden at a new location or in a changing environment. No need to read from cover to cover or in one fell swoop to get the most out of this book. Each chapter can stand by itself as, in most cases, can each section within a chapter.

So dip in at out of this book according to your whims, the seasons, or what''s happening in your garden. Science may seem out of place in so bucolic an activity as gardening. After all, millions of years of evolution have prompted seeds to germinate and plants to grow in soils and climates as diverse as the Arctic tundra, the Arizona desert, and my garden in New York''s Hudson Valley. As soon as I acquired some knack of gardening, I could have carried on from there, just dropping seeds each year into furrows, cozying roots of new trees into the ground, lopping back some branches of my roses, and expect, mostly, business as usual. All of which would result in a pretty enough scene and reasonably good harvests of tomatoes, raspberries, and other edibles. To me, gardening can be something more than this business as usual. Being familiar with what''s going on behind the scenes - that is, some of the natural science behind what''s happening, or could happen, out there within the confines of the garden gate - not only makes for more bountiful harvests, and more beauty and aroma from the garden, but also more fun and more interest. The genesis for this book came to me one day as I was piling scythed meadow plants and horse manure, along with old vegetable plants and sprinklings of soil and dolomitic limestone, into one of my compost bins.

I realized that what I was adding to the pile, and how much of each ingredient, even how I fluffed them up or patted them down with my pitchfork, and then watered, all reflected what I had learned over the past 40 plus years of gardening. My classroom has been the garden itself, and actual classrooms, as well as what I''ve gleaned from magazines, books, and scientific journals, and from conversations with other gardeners and agricultural scientists. My garden education has been unusual. Growing up in the suburbs, I remember only a small vegetable garden whose tenure was soon eclipsed by a swing set. Wait! There was a potted banana tree and one hyacinth bulb that I nurtured under the purple glow of a ''Growlite'' in the basement during high school. And a single potted cactus that I bought to adorn my bedroom windowsill in graduate school. Hints of future interest? Perhaps. Graduate study in those cactus days was in chemistry, a continuation of an interest kindled by my high school chemistry teacher.

But coming to the conclusion that graduate study in quantum chemistry was not going to answer any fundamental questions, I dropped out, moved to Vermont, and got the gardening bug. Because I was living in a third floor apartment, I expressed that gardening bug with a voracious appetite for books, reading about gardening. A year later, I decided to dive into agriculture in earnest, and was fortunate to land in a graduate program in soil science. My interest and education in chemistry proved a good foundation for soil science which, in turn, proved a good foundation for my next course of study. A small plot of land began my education "in the field" and complemented my academic studies. With access to one of the best agricultural libraries in the country, I also rounded out my education plying my way through volume after volume of books on gardening and related topics. (I remember coming across a whole book on lettuce seed!) Eight years later, I had two framed diplomas to hang on my wall, one for a master''s degree in soil science, and the other for a doctorate degree in horticulture, and I was still gardening with the same exuberance and learning about gardening through experience, the printed word, and contact with other gardeners and agricultural scientists. Thinking back, how little I knew about gardening.

And so it goes. Back to my compost pile . As I added the meadow hay to the pile, I took into account the cut plants'' youthful lushness, which influences their ratio of carbon to nitrogen, as I layered them in the bin with the horse manure. Manure is usually thought of as a high nitrogen material, but I looked at what was in the cart and, taking into account the amount and kind of bedding (wood shavings) with which it was mixed, made a rough estimate in my head of how much to use to make a good balance with the meadow plants. When the pile was finished, I checked my work by monitoring the temperature of the pile''s interior with a long-stemmed compost thermometer. Etc., etc. There''s some art in making compost.

But also science. With this book, I hope to show you, the reader, how knowing a little of the natural science behind what''s happening out in the garden can make for a lot better garden in terms of productivity, beauty, plant health, sustainability . and interest. All of which makes for a perennially "young gardener!" PROPAGATION AND PLANTING You wouldn''t think that the dead of winter would be a good time to sow seeds. But it is, for plants whose seeds need some kind of long term treatment before they will sprout. Such is the case for tree peony seeds I recently planted. But "planted" is really too gardenesque a term for what I did with those seeds. After soaking them in water a few hours, merely tossed into plastic sandwich bag with a handful of moist potting soil.

They will sit on a kitchen counter couple of months, then go into the refrigerator another few months. Peony seeds need this treatment because they must lay down roots before any shoot growth can begin. To grow, those roots need some rain (or a good soaking) to leach inhibitors from the seeds, and some warmth. The shoots, however, won''t sprout until they''ve been exposed to a period of cool, moist conditions -- outdoors or in my refrigerator. Under natural conditions, all this might take two years. In my house, all systems should be go by spring. Lily and viburnum seeds also respond to this type of treatment. A reluctance to sprout as soon as touching down on moist soil often makes sense for ensuring the survival of the tender, young seedlings.

Not rearing their heads until convinced that winter is over and they have the support of established roots system is just the ticket for survival of wild tree peony seedlings in a climate characterized by cold winters and periodic drought. Germination quirks of other kinds of plants'' seeds reflect other natural environments. Some seeds have a double dormancy, one for the seed coat and one for the embryo. Still others -- goldenseal, for example -- ripen with underdeveloped embryos. The same warm, then cold, treatment needed by tree peonies also prepares seeds with either of these quirks for germination. Where moisture is more or less consistent throughout the year, it is winter cold that would kill a young sprout that began growing in the fall. Fall-ripening seeds won''t sprout until they feel that winter is over, a condition that could be mimicked by a couple of months in the refrigerator in a sandwich bag along with moist potting soil. After doing time in the refrigerator, it''s not unusual for a whole batch of seeds to sprout in unison, as if a switch has been turned on, even before they''re released into warmth.

That cool, moist treatment is called stratification because in the past nurseries effected this treatment by spreading alternating layers of seeds and soil in flats kept outdoors for winter. Hormones within seeds are what brings them to life at the appropriate moment. Although lying apparently lifeless in a bag on a refrigerator shelf, all sorts of things -- hormonally -- are going on. Levels, for instance, of a germination inhibitor called abscisic acid are decreasing while levels of another hormone, gibberellic acid, are increasing. These hormones have been extracted from seeds and synthesized. Some seeds shed their normal reluctance to sprout with nothing more than a dip in an appropriate concentration of gibberellic acid. All is not so simple, though, because other hormones also are at work, and other compounds, such as potassium nitrate, hydrogen peroxide, or malt extract can also promote germination. Not all fall-ripening seeds need stratification before they will germinate.

Two examples of tree seeds in this class are those of catalpa and those of sycamores (although sycamore''s relative, the London planetree, does need stratification). Perhaps catalpa and sycamore seeds have evolved without a need for stratification because they hang on the trees late enough into the winter so that, by the time they drop to moist ground, temperatures are too cold for germination. Or else it''s spring, and just the right time for germination. Let''s not blame dormancy only on hormones; some seeds stay asleep for purely mechanical reasons. The tough seed coats of honeylocust, black locust, and black cohosh are among those that can''t imbibe water as soon as their seeds hit the ground. A seed that remains dry inside will not sprout.