Suppose you have a favorite tree and you’d like to have another just like it. Can you grow a new one from seed? After all, nature does it all the time.
Yet a tree in the forest bears tens of thousands of seeds every year — millions over its lifetime — and only a handful of them will ever become mature trees.
Before you try to grow trees from seeds or nuts such as acorns, research the particular techniques that are needed for the tree species. (Beth Botts/Morton Arboretum)
“A seed has to overcome a lot of obstacles to sprout and survive,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “If you’re going to grow a seed into a tree, you need to help it by providing specific conditions that are different for every species of tree.”
Seeds sprout in particular ways that depend on where and how each species evolved. “You can’t treat them all the same,” she said.
If you’d like to try starting tree seeds, begin by learning about the species, how it reproduces and what its seeds need. Here are some things to think about:
Timing. Learn when your tree drops its seeds and when you need to plant them. For example, a silver maple sheds seeds in late spring, while white oaks drop acorns in late summer or early fall. In both these species, seeds will only sprout if they are planted within a few weeks. “Depending on the tree, there may be a narrow window for planting, or you may need to hold onto the seeds for months,” Yiesla said.
Maturity. Only seeds that are fully mature will germinate. “For each species, there’s a best time and method to harvest seeds,” she said. For example, to harvest most pine seeds, snip cones from the tree in late summer when the cones’ scales are still closed, but the seeds enclosed by the scales are ripe. Once the scales dry out, they will separate to free the seeds.
Cold. Many trees that are native to cold climates, such as walnut, cherry and juniper, have seeds that mature in fall but need to spend time in the cold in order to germinate. This chilling period is called cold stratification. The length of cold needed varies by species.
Seed coats. Some seeds, such as those of black walnut and Kentucky coffeetree, have hard shells or seed coats that must be penetrated for the seed to sprout. This may be done by soaking the seeds in water or by using a tool to nick a hole in the seed coat.
Tap roots. In some species, such as hickory and some kinds of oak, the seedlings will develop a main root that grows down, called a tap root. In other species, such as birches and maples, seedlings grow a wider network of fine root fibers. “Tap-rooted trees are more difficult to transplant,” Yiesla said. Over time, even in tap-rooted species, most tree roots will spread out horizontally just beneath the soil.
Quantity. “You’ll need to start a lot of seeds to get a few plants,” she said. “That’s how trees do it.”
Animals. Think about protecting your seedling bed or collection of pots from animals that will dig for the seeds or nibble the fresh young growth. “In a forest, most tree seedlings end up as animal food,” she said.
Variation. Trees you start from seed will only be like their parents if they are straight species, not cultivated varieties. That’s because seeds are made through sexual reproduction, which introduces genetic variation. Cultivars such as the Honeycrisp apple or the Royalty flowering crabapple tree must be propagated by grafting, not grown from seed, to maintain characteristics such as flavor or abundant flowers that make them distinctive and marketable.
“It can be fun and satisfying to grow a few trees from seeds,” Yiesla said. “It can also be challenging. Your chances of success are much greater if you’ve investigated the needs of the tree you’re trying to grow.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
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