Planting seeds is a satisfying way to grow trees and shrubs. Gardeners often have a special affection for plants produced in this manner.
Don’t be put off by the length of time required to grow trees and shrubs from seeds. Unless you are interested in flowering or fruiting (which may take a decade for some plants), you can expect plenty of new growth from many species of young tree and shrub seedlings. And even if years are required, shouldn’t some aspects of gardening be long-term propositions?
Seed-grown plants, unlike cuttings and grafts, are not genetic replicas of their parents. With some species, such as green ash, each seedling may be noticeably different in form or leaf color. At the other extreme is Amur honeysuckle, seedlings of which are almost identical to each other and their parents.
In the case of a tree or shrub with a wide natural range, starting with collecting or purchasing seeds from plants grown under similar weather and soil conditions will increase the likelihood that the seedlings will adapt well to your property.
Obtaining seed is just the first step. I remember one autumn day decades ago, when with high aspirations I dropped an apple seed into some potting soil in an eight-inch flowerpot. No, that seed hasn’t by now grown into a majestic old tree.
It germinated, and the tree started to grow. Then it stalled at about four inches in height. Apple seeds, like those of many other hardy trees, need special pre-treatment before they will germinate and grow.
Tree seeds planted as I planted them often do not grow at all. This behavior is not without logic. If an apple or sugar-maple seed germinated as soon as it touched ground in late summer or early autumn, the life of the tender young seedling would be snuffed out with the first frosty autumn night. Seeds that ripen in autumn usually have an innate mechanism that prevents them from growing until they have become convinced that winter is over.
The way to fool such seeds into behaving as though winter were over is by keeping them cool and moist for a couple of months. By packing seeds into plastic bags along with slightly moist peat or sphagnum moss and then putting the bags into a refrigerator, I’ve successfully grown many trees from seeds. Creating this artificial winter for seeds is known as stratification, because nursery workers chill large quantities of seeds by packing alternating layers (strata) of seeds and moist sphagnum moss into boxes.
Seeds could be sown directly in the ground outside, but this imperils them to squirrels, birds, flooding, and other natural hazards.
Seeds kept cool and moist sprout once they have accumulated a certain number of hours of chilling. The chilling requirements vary with the species as examples, one month for Chinese elm, two months for apple, two to four months for hemlock, and four months for dogwood. The optimum chilling temperature is 32 to 40 degrees Fahrenheit, and no time is put into the chilling “bank” when the temperature gets too cold, below about 32 degrees, or too warm, above about 50 degrees Fahrenheit.
A hard seed coat that water cannot penetrate is another common roadblock to germination. To make such seeds permeable (a process known as scarification), either nick them with a file or pack them in plastic bags with non-sterile soil or compost for two or three months, so microorganisms can chew away at the hard coating.
Some seeds — silk tree, honeylocust, locust, and Kentucky coffee tree are examples — germinate as soon as they are scarified. Others, such as redbud, juniper and hophornbeam, need stratification following scarification to germinate.
Not all tree seeds need any sort of treatment before they’ll germinate. Catalpa and sycamore, for example, germinate as soon as they are sown. Their seeds hang on the trees through winter. The evolutionary logic in their germination behavior may be that by the time their seeds drop to moist ground temperatures are too cold for germination. Or else it’s spring, and just the right time for germination. Seeds that ripen in the spring, such as silver maple and red maple, also need no treatments.
Once seeds are ready for planting, perhaps already sprouting, I either pot them in containers in regular houseplant potting soil, or else plant them in the ground outside. Plants with taproots, such as hickories, pawpaws and walnuts, need deep containers. Or I make them from sections cut from four-inch-diameter plastic pipe with screens wired to their bottoms.
The length of time I grow a plant in a container varies, depending on the type of plant, but I check the roots periodically to make sure to either repot or transplant to open ground before the roots become potbound.
Before planting a seedling in a permanent location, I try to picture the tree or shrub 30 years hence. That special affection one develops for woody plants raised from a seed makes it especially hard to cut such plants down, even if they are in the wrong place.
“Tall oaks from little acorns grow.” Likewise for maples, sycamores, junipers, and other trees.
In addition to collecting seed myself from local trees, I turn to www.jlhudsonseeds.net for more obscure tree and shrub seed,
My own book, The Ever Curious Gardener, offers details and techniques for growing a wide variety of plants from seed. Plant Propagation: Principles and Practices by H. Hartmann and D. Kester details principles and practices of propagation for all sorts of plants.
New Paltz writer Lee Reich, also author of The Pruning Book, Weedless Gardening, Growing Figs in Cold Climates and other books, is a garden consultant specializing in growing fruits, vegetables and nuts. He hosts workshops at his New Paltz farmden. For information, go to www.leereich.com.
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