Growing techniques from seeds

Seed planting is a satisfactory method of growing trees and shrubs. Gardeners often have a special affection for plants produced in this way.

Don’t be alarmed by the long time required to grow trees and shrubs from seed. Unless you are concerned with flowering or fruiting (which can take a decade for some plants), you can expect a lot of new growth from many types of tree seedlings and small shrubs. Even if it takes years, shouldn’t some aspects of gardening be long-term propositions?

Plants grown from seeds, unlike cuttings and grafts, are not genetic copies of their parents. In some species, such as the green ash, each seedling may differ markedly in shape or leaf color. At the other end is the Amur honeysuckle, whose seedlings are almost identical to each other and to their parents.

In the case of a tree or shrub with a wide natural range, starting by collecting or purchasing seeds from plants grown in similar climate and soil conditions will increase the likelihood that the seedlings will adapt well to your property.

Getting seeds is just the first step. I remember one fall day decades ago when, with high ambitions, I dropped an apple seed into the fertile soil of an eight-inch diameter flower pot. No, that seed has not yet grown into a majestic ancient tree.

It sprouted, and the tree began to grow. Then stop at about four inches high. Apple seeds, like the seeds of many other hardy trees, need special pre-treatment before they can sprout and grow.

Tree seeds planted as I planted them often do not grow at all. This behavior is not devoid of logic. If an apple or sugar maple seed germinates as soon as it hits the ground in late summer or early fall, the life of the delicate little seedling will end with the first frosty night of fall. Seeds that ripen in the fall usually have an innate mechanism that prevents them from growing until they are convinced that winter is over.

The way to trick these seeds into acting as if winter is over is to keep them cool and moist for a few months. By packing the seeds in plastic bags with slightly damp peat or sphagnum moss and then placing the bags in the refrigerator, I have successfully grown many trees from seed. Establishing this artificial winter for seeds is known as stratification, because nursery workers cool large quantities of seeds by packing alternating layers (layers) of seeds and moist sphagnum moss into boxes.

Seeds can be planted directly into the ground outside, but this exposes them to danger from squirrels, birds, floods and other natural hazards.

The seeds remain cool and moist and germinate once they have accumulated a certain number of cooling hours. Chilling requirements vary by species eg one month for elm, two months for apple, two to four months for hemlock, four months for dogwood. The optimum cooling temperature is 32 to 40 degrees Fahrenheit, and no time is placed in the cooling “bank” when the temperature gets too cold, below about 32 degrees, or too warm, above about 50 degrees Fahrenheit.

The hard seed coat that water cannot penetrate is another common obstacle to germination. To make these seeds permeable (a process known as scarification), either cut them with a file or pack them in plastic bags with non-sterile soil or compost for two or three months, so that microorganisms can chew through the tough layer.

Some seeds—the silk tree, honey locust, locust, and Kentucky coffee tree are examples—sprout once scratched. Others, such as red bud, juniper, and walnut ray, need stratification after scarification in order to germinate.

Not all tree seeds need any type of treatment before they germinate. For example, catalpa and sycamore sprout as soon as they are planted. Their seeds hang on trees during the winter. The evolutionary logic in their germination behavior may be that by the time their seeds have fallen to the temperatures of the moist earth they are too cold to germinate. Otherwise, it is spring, which is the right time for germination. Seeds that mature in the spring, such as silver maples and red maples, also do not need treatment.

Once the seeds are ready to be planted, and may have already germinated, I either pot them in containers in regular houseplant soil, or plant them in the ground outside. Root-rooted plants, such as walnuts, papayas, and pecans, need deep pots. Or make them out of sections cut from four-inch plastic tubing with wire mesh on the 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 they are repotted or transplanted into open ground before the roots become pot bound.

Before I plant a seedling in a permanent place, I try to imagine the tree or shrub in 30 years. This special affection that one acquires for woody plants obtained from seeds makes these plants particularly difficult to cut, even if they are in the wrong place.

“Tall oak trees grow from small acorns.” The same applies to maple, sycamore, juniper and other trees.

In addition to collecting seeds myself from local trees, I head to www.jlhudsonseeds.net for more seeds of obscure trees and shrubs.

My own book, The Ever Curious Gardener, provides details and techniques for growing a wide range of plants from seed. Plant reproduction: principles and practices By H. Hartmann and D. Kester details propagation principles and practices for all types of plants.

New Paltz writer Lee Reich is also the author of Pruning book, weedless gardening, growing figs in cold climates And other books. He is a garden consultant specializing in growing fruits, vegetables and nuts. He hosts workshops at his New Paltz farm. For information, go to www.leereich.com.