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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

A Bit Of Deception Lets Me Get Some Seeds To Sprout That Under Natural Conditions Would Wisely Stay Asleep

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 for a few hours, I merely tossed them into a plastic sandwich bag with a handful of moist potting soil. The bag will sit on the kitchen counter for a couple of months, then go into the refrigerator for another couple of 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. These are examples of seeds that need scarification before they can be stratified.

In nature, tough coats are eventually softened as soil microbes chew away at them, by cycles of freezing and thawing, by abrasion, and by passage through animals. Microbes work best at warm temperatures, so a couple of months in a sandwich bag along with some potting soil could awaken these seeds just as they do those of tree peonies. The potting soil, in this case, should contain some real soil or compost to supply living organisms to work on the seed coats.

Scarification means "to scratch" and with large enough seeds, I take this meaning literally, with a file. Nicking seeds or nipping out a little piece of seed coat with a wire cutter are other ways to let water in past a tough seed coat. Quicker ways to scarify a batch of seeds are with very hot water, even sulfuric acid, but care is needed not to kill the seeds. As a general rule, bring almost to a boil 5 times the volume of water as volume of seeds, then pour the water over the seeds and let them stand in the water for 12 to 24 hours. With sulfuric acid, suffice it to say that familiarity with using this caustic chemical is needed, along with goggles and gloves. Timing is critical, and varies with the kind of seed. The acid must be thoroughly rinsed off following the treatment.

The easiest pretreatment is that needed by many grasses and most annual flowers and vegetables. Seeds of these plants need nothing more than a period of dry storage of from one to six months before they'll germinate. Cold is not needed, but does keep them fresh longer — so my vegetable and flower seeds wait out winter sitting in airtight plastic boxes and Mason jars in my garage.

Burial In Tundra Might Be Ideal For Seed Storage But I Choose More Practical Storage For My Vegetable And Flower Seeds

Few seeds have as short a viability as onion; after only year they might not be sufficiently viable for sowing.

A better story is the reported longevity of the 10,000 year old lupine seed that germinated after being taken out of a lemming burrow in the Yukon permafrost. Just think: This same species was up and growing when humans first walked crossed the Bering Land Bridge, and saber-toothed cats and woolly mammoths may have brushed up against its leaves. Except that the story of the 10,000 year old lupine seed turns out to be apocryphal, as confirmed by radiocarbon dating.

The true record for seed longevity was, until recently, 2,000 years, and held by a date palm grown from seed recovered from an ancient fortress in Israel. A more recent discovery broke that record by a long shot.

A kind of campion seed (Silene stenophylla) found buried, this time in a squirrel burrow, in Siberian tundra could very well be 32,000 years old. The seed sprouted and was grown into a charming, white-flowered plant. Some coaxing was needed to get that seed to sprout. Actually, the seed itself did not sprout, but new plants were propagated from a few cells that were removed from the placenta and multiplied under sterile conditions on a specially concocted growth medium. Once cells had multiplied sufficiently, the growing medium was altered to induce leaves, stems, and roots, and eventually the plants were robust enough to be planted in soil. The plant flowered and set seed, which germinated readily to produce more seedlings.

As short as is onion seed viability (I purchase new seed every year), other seeds have even shorter viability. Seeds in the family Tillandsioideae, related to pineapple, probably hold the record, with a viability of 4-6 weeks. Silver maple, Acer saccharinum, seeds retain their capacity to germinate for only about a week, making the many silver maples in the view out my bedroom window testimonial to the trees' fecundity or the seeds fertility.

Viable seeds are living, albeit dormant, embryonic plants which do not live forever. It's wasted effort to sprinkle dead seeds into furrows either in the garden or seed flats.

When purchasing a packet of seeds from a local store or mail-order seedhouse, you are assured of the viability of the seeds. There are government standards for the minimum percentage of seeds that must germinate for each type of seed. The packing date and the germination percentage often are stamped on the packets. (The germination percentage must be indicated only if it is below standard.) I write the year on any seed packets on which the date is not stamped.

Old, dog-eared seed packets may or may not be worth using this season. It depends on where the packets were kept and the types of seeds they contain.

Conditions that slow biological and chemical reactions also slow aging of seeds, i.e. low temperature, low humidity, and low oxygen. During spring and summer, the airtight plastic boxes and Mason jars in which I store seeds find their low temperature and low humidity home in the depths of my freezer or, more recently, in the cool temperatures of my basement. By fall, when frozen fruits and vegetables claim freezer space, I move seed boxes and jars back to the garage. An easy way to keep the humidity low in the storage containers is to sprinkle in some powdered milk, from a freshly opened box, or with silica gel. Renew the powdered milk each year. Silica gel can be renewed in a hot oven.

There's no practical way for the backyard gardener to store seeds in a low oxygen atmosphere. I did, however, reverse engineer a bicycle pump to become a weak vacuum pump which, along with a Foodsaver®, evacuates some of the air from my seed-containing Mason jars. Thinner air is also drier air.

Although some seed companies market their seeds in hermetically sealed, plastic-lined foil packets, I've never noted superior germination from these foil packets, as compared with plain old paper packets. Matter of fact, my own casual observations over the years is that germination of seeds kept in these hermetically sealed packets is worse. Perhaps the extra cost of the packaging is a disincentive to a seedhouse to discard old seeds or open the packets for re-testing. Perhaps my casual observations are too casual.

Seeds differ in how long they remain viable. Except under the very best storage conditions, as with onion seed, it's not worth the risk to sow parsnip or salsify seeds after they are more than one year old. Two years of sowings can be expected from packets of carrot, and sweet corn seed; three years from peas and beans, peppers, radishes, and beets; and four or five years from cabbage, broccoli, brussels sprouts, cucumbers, melons, and lettuce.

Among flower seeds, the shortest-lived are delphiniums, aster, candytuft, and phlox. Packets of alyssum, Shasta daisy, calendula, sweet peas, poppies, and marigold can be re-used for five or ten years before their seeds get too old.

In a frugal mood, I might do a germination test for a definitive measure of whether an old seed packet is worth saving. Counting out at least 20 seeds from each packet to be tested, I spread them between two moist paper towels on a plate. Another plate inverted over the first plate seals in moisture and the whole setup then goes where the temperature is warm, around 75 degrees. After one to two weeks, I peel apart the paper towels and count the number of seeds with little white root "tails". If the percentage is low, the seed packet from which the seeds came gets tossed into the wastebasket or compost pile. (I don't give them away!). Or, I might use the seeds and adjust their sowing rate accordingly.

No one knows exactly what happens within a seed to make it lose its viability. Besides lack of germination, old seeds undergo a slight change of color, lose their luster, and show decreased resistance to fungal infections. There is more leakage of substances from dead seeds than from young, fresh seeds, so perhaps aging influences the integrity of the cell membranes. Or, since old seeds are less metabolically active than young seeds, the old seeds leak metabolites that they cannot use.