By Mark and Ben Cullen
Of all nature’s miracles, trees seem most profound.
Standing under a towering native silver maple in the park across from Ben’s house, it’s hard to imagine these mighty specimens starting from a tiny maple key like the thousands we drag our feet through each spring.
Most nursery-grown trees we buy do not start life this way. They are usually grown from cuttings, which jumpstarts their growth in the early years. Propagating trees from cuttings is reliable and expedient, but it does limit genetic diversity of our tree species. In our view there is nothing so miraculous as watching a tree seedling push through the soil and mature into a strong, woody specimen.
There are other benefits to starting trees from seed. If the seed is locally sourced from a native forest, the genotype will be adapted to its specific region. Unlike a tree grown from a cutting or grafted, the genetics of a locally seed sourced tree is unique and adapted to its growing zone.
Seed collection
The thrill of the hunt is one reason to collect seeds, and it is free. Now is the perfect time of year to be looking for tree seeds – they are abundant and ripe for harvest for many hardwood species such as oaks (acorns), maples and walnuts as well as shrubs such as juniper and dogwood. A ripe seed should pluck off the plant easily. Standing on a mound of snow may provide better access than later in the season. If you find a tree seed on the ground that has started to germinate, so much the better. Mark is harvesting dozens of young black walnut and Burr oak trees that were sown by forgetful squirrels.
A few things to keep in mind: arboretums and botanical gardens are out of bounds for seed collection, as their seed stock are often depended upon for research. In the wild, the foragers rule of thumb applies, take no more seed than you need.
From seed to seedling
Prepare seeds for propagation by cleaning them. Winged seeds of elm, linden, maple, ash and birch should be left whole – they land in the ground in one piece and the seeds are evolved to push through these soft shells. For chestnut, butternut and walnut, think like a squirrel – remove the husks. For seeds embedded in fruit, such as most “berries” (dogwood), the seeds need to be removed from the fruit to germinate.
Breaking dormancy is required to get most hardy trees and shrubs to germinate. In nature, this happens over the course of winter – deep, damp cold followed by warm spring temperatures encourages seeds to germinate. When we mimic this process, it is called stratification. Red oak and sugar maple are two reliable species to start with as they respond well to a basic treatment.
Soak the seeds or acorns in water at room temperature for 48 hours, then transfer them to a well drained plastic pot or seed starting tray containing a mix of 50 percent wet sand and 50 percent peat moss. Or look for “seed and cutting mix” at your garden retailer. Put the container into the fridge, not the freezer, and leave it for 90 to 120 days, mimicking a winter.
Planting the seed
Now that you’ve done the work of stratifying your seeds, move them to a container with potting mix and plant the seed about twice as deep as the seed is thick. If you have a cold frame, this is a perfect use for it – keep the containers in the cold frame until you have decided where to plant your tree in the garden. Otherwise, put the seedlings under lights or in a window where you might start veggie seeds. This will give them a head start for the growing season.
Plant out come spring
This time of year, many seeds make attractive seasonal decorations, for the mantle or the dinner table. A bowl of chestnuts, acorns, the seed heads of bittersweet vine and pinecones are all good choices.
Mark Cullen is an expert gardener, author, broadcaster, tree advocate and Member of the Order of Canada. His son Ben is a fourth-generation urban gardener and graduate of University of Guelph and Dalhousie University in Halifax. Follow them at markcullen.com, @markcullengardening, and on Facebook.
