Standing Under The Bigleaf Maple
Bigleaf maple, known scientifically as Acer macrophyllum, is a stately deciduous tree native to western North America. Join native plant gardener Jerad Bryant as he explores why this tree isn’t widely planted in landscapes, and discover why it should be.
Bigleaf maple trees sprout flowers and foliage during early spring.
There are a million reasons to plant a tree. Thomas Fuller says it best when he said “He that plants trees loves others besides himself.” A tree is an investment for the future because it provides shade, resources, and artistic inspiration to all who watch it as it matures. The tree planter may never see their tree reach maturity, and that is exactly why planting a tree is as much for the self as it is for the community.
Certain trees are rarely, if ever, planted into residential and commercial landscapes. One such tree, the Pacific Northwest native bigleaf maple, has a bad reputation in gardens. Its scientific name is Acer macrophyllum, and it is a beautiful tree that offers plentiful resources for local ecosystems. It also grows softwood that easily breaks. Every time a rough storm or strong gust of wind comes through, bigleaf maples often crack and break, dropping huge chunks of their canopy onto the ground below.
Perhaps this is why there are barely any bigleaf maple tree cultivars. Because the tree struggles to sell commercially and is mainly used for timber, there is less of an incentive to breed new cultivars from it. Some do exist though, like Acer macrophyllum rubrum with red new growth, and A. macrophyllum kimballi with triple samaras (the winged seed pods).
In the forest, this phenomenon of branch breakage is wonderful! Deadwood on the forest floor is a boon for insects, fungi, and bacteria. They ravenously devour the wood, and they leave soft, fertile humus for other trees and shrubs to germinate in. Maybe a few plants or animals get damaged as the tree’s branches fall, but other than that the damage is minimal.
Near a home, or at a park, a falling tree branch may cause structural damage, and it may hurt people if they are close by. This is often the reasoning behind not planting a bigleaf maple in the yard or landscape. I wonder though, how much of this is fear-mongering, and how much of it is true?
Should You Plant A Bigleaf Maple?
We must consider other factors before deciding to reject bigleaf maple in the landscape outright. First of all, in a forest setting, trees often lean on each other, and their roots are intertwined underneath the topsoil. When a storm comes through, this network of trees relies on each other for support, and they are stronger together than they are alone. It may be difficult to do this in a small garden, however planting multiple trees close to each other can simulate forest conditions. As the trees mature, they lean on each other aboveground and belowground.
Bigleaf maples grow giant leaves that reach 12 inches wide!
A second reason, and I think the main reason behind the bigleaf maple smear campaign, is that these trees grow to be ginormous specimens! They often reach heights of 75 - 100 feet and widths of 50 feet as they mature over 200 years. In the small garden, this tree dwarves shrubs, houses, and yards. The eventual large mature size may be scary for homeowners, however, it is also the reason why this tree is loved and treasured by us humans and by wildlife.
In the forest, this large tree attracts mosses, lichens, and ferns that love growing on its ridged bark. If you look up in a Pacific Northwest forest and see a deciduous tree covered in green moss, it is most likely a bigleaf maple. Licorice fern, Polypodium glycyrrhiza, uses this tree as a host and spreads profusely on it in the fall, winter, and spring. The huge leaves for which the tree earned its name are rich in nutrients, and they provide food for a wealth of microfauna in the soil. Birds and rodents love the winged samaras holding the seeds, and you’ll often see squirrels munching on the seeds.
Whether or not to plant a bigleaf maple depends on your situation and how much space there is in the landscape. For commercial landscapes and park plantings, this tree is a great way to invite the forest back into urban settings. Animals, bugs, fungi, and bacteria will thank you for giving them a tree with ample natural resources. For small gardens, streets, and areas close to buildings, bigleaf maples are an excellent choice but may require additional maintenance to keep the area safe. Pruning, annual trimming, and shaping allow this tree to grow big and strong in these urban settings. If you are unsure whether you should plant one or not, consider speaking with a licensed arborist or a native plant nursery worker and determine if your area is hospitable to Acer macropyllum.
Gardening Underneath Bigleaf Maple
Landscaping under this tree proves difficult, especially with non-native plants that haven’t evolved alongside bigleaf maples. Try selecting Western sword fern, trillium, and Oregon grape to grow under this tree. These plants tolerate the shade cast by the tree, and they manage to grow despite the bigleaf maple sucking up all the water in the soil in the summertime. Other shade plants like hostas and bleeding hearts struggle to grow under this tree with the intense shade it casts and a lack of adequate soil moisture. Select native dry shade-loving plants, and you’ll have an elegant garden below the graceful stature of this amazing native tree.
Bigleaf maple is polygamous, and grows male and bisexual flowers. This cluster has mostly male flowers.
Sexual Reproduction
This tree repopulates forests using a very clever strategy called polygamy in plants. As the name suggests, polygamy in trees involves trees having multiple partners that they share pollen with. It also implies that the tree has a combination of male-only, female-only, and bisexual flowers at the same time. Bigleaf maples have many male flowers and a few bisexual flowers with male and female reproductive organs.
This flower cluster has bisexual flowers with protruding stigmas.
What does this mean for the grower? Well, it means that your tree produces seeds that are a mix of many bigleaf maple trees’ genetics. In the wild, this strategy leads to new evolutionary advantages as the trees readily create new genetic sequences in their DNA for adaptations to the local environment. Let’s say the climate keeps warming. As bigleaf maples experience this warming, they may pass down genes that allow for increased heat tolerance in the summer. Although a hypothetical situation, this simulation shows that this tree has the tools it needs to readily adapt to its changing surroundings. It is further reflected in the tree’s wide range, as bigleaf maples grow from Southern California up through British Columbia, and even in parts of southern Alaska.
Look closely at these flowers, and you’ll see that a few have protruding stigmas. The majority of flowers are filled with anthers covered in pollen. All it takes is a few gusts of wind or a bunch of traveling insects, and that pollen goes deep inside the stigmas’ styles to fertilize the flower’s ovules. Then, winged samaras develop, and they helicopter down to the ground when the seeds are ready for germination.
Propagation
If you garden in the Pacific Northwest, propagating a bigleaf maple is like propagating a weed. Its seeds germinate readily and rapidly, and the seedlings mature quickly. In the spring, wait for bigleaf maples to drop their samaras. Then, collect samaras with viable seeds inside them. Sow the samaras in pots with potting soil or a mineral-based mix, and water well. Seeds germinate in their first year, and they mature quickly. Transplant mature seedlings into the garden once they have plenty of roots.
This tree also sprouts readily from cuttings and cut stumps. To propagate via cuttings, take softwood cuttings in the winter and keep them cool. Then, in the early spring, take them out of cold storage and plant them in pots with potting soil. Add a humidity dome in areas with low humidity levels. Keep the cuttings moist, and they should sprout roots within a few weeks. Transplant rooted cuttings into the garden, and watch them mature into beautiful big trees.
Final Thoughts
If I owned a half-acre, I would plant a bigleaf maple and watch it mature over my lifetime. I love this tree and have settled with watching the ones grow near me by the Willamette River. Until I can plant my own, I ask you, “Can you please plant one for me?”
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