Bigtooth Maple, Acer grandidentatum, is native to the far southwest corner of Colorado in a place known as Sleeping Ute Mountain. It is common in canyons, northfacing slopes and along mountain streams in Utah, Wyoming and west Texas from 5000′ to 8000′. Although most often listed as a separate species, Bigtooth Maple is sometimes called Western Sugar Maple, therefore, a subspecies of Acer saccharum. Its other names are Canyon Maple and Wasatch Maple.
Even though this beautiful native tree is given an “A” rating in the Front Range Tree Recommendation List, two local arborists admitted that they hardly ever see one. And even though I was an arborist for 25 years in Boulder, I can only remember seeing one big specimen. For a Bigtooth Maple, big is 25′-30′, occasionally to 40′. Allan Taylor is a Boulder horticulturist and selector of many great natives including a hardy blue Arizona Cypress and Taylor’s Sunburst Pine. I asked him why there are so few Bigtooth Maples locally. He said, “People are afraid to plant a tree they don’t know, and growers are afraid to propagate trees that might not sell.” Allan planted one years ago in his Boulder yard that is now 25′ tall and turns a gorgeous orange-red in the fall.
In the wild, Bigtooth Maple can have a range of fall colors from yellow-orange to deep orange-red, varying with the season.
Some people, like Allan, get a tree of known red color grafted onto a native rootstock. Scott Skogerboe, head propagator at Ft. Collins Wholesale Nursery, collects seeds from the best red Bigtooths growing in Ft. Collins. Tim Buchanan, former city forester of Ft. Collins, planted quite a few along the streets that were grown from Wyoming and Utah seed. These are doing well. Scott said they are tolerant of little water, alkaline conditions and that some are single stem and some are multistem in habit. One type of Bigtooth called Manzano is considered another subspecies with good reddish fall color. Scott learned that this one in particular should be winter-watered to prevent die-back.
At first when Scott was growing them from seed, although they germinated well, they grew very, very slowly. He wondered if they needed a particular fungal partnership. On a trip to Utah, he was shown a grove of very large Bigtooth Maples, so he collected some soil from around the roots and put this soil around a 12″ specimen in his own yard. In a year’s time it grew to 7′, so he knew to spend the money to get mycorrhizae from Mycorrhizal Applications. That company was later bought by a giant Japanese chemical company who supplied a cheaper selection of species. However it is interesting to note that this megacorporation has a motto: “business interest must always be in harmony with public interest.” Scott now has found another of their formulations that works.
Allan Taylor believes that, based on his experience, Bigtooth Maple really needs no special treatment. Ken Fisher, forester for the City of Boulder says he plants a lot of trees and that he has an 80% success rate with most of them, but only a 50% or less rate with Acer grandidentatum. He has tried giving them extra water to establish and that didn’t seem to work. He does plant 2″ caliper B&B trees and he thinks thaat smaller trees might be easier to get started.
David Buckner has 45 years experience in field plant ecology with an expertise in soils. He planted a Bigtooth in Boulder 40 years ago that established well, but since he moved to a new house he has lost 3 Bigtooths after planting them. He says in nature they grow in areas with little competition and the grass keeps moving in on his new trees. Gary Meis, professional propagator of natives, said that even in nature a plant species can thrive in one location and not in another that is nearby. He, like Scott, would try taking a little soil from around a successful tree to collect the mycorrhizae that was partnering with it.
Dan Johnson, curator of native plants at Denver Botanic Gardens has a nice Bigtooth in his yard. He doesn’t do anything special for it, just good, well-drained soil, not watered more than once a week. Both Allan and Scott were quick to say that this native maple should be planted more. Ken Fisher would love to have more growing in Boulder, and David Buckner is determined to try planting another one.
I tracked down David’s 40 year-old Bigtooth, growing in the Table Mesa area of Boulder. It is now 40 feet high and 25 feet wide, multistemmed and looking very healthy. It is sited 30′ north of the house with a big spruce on the west side and another spruce nearby to the southeast. It is growing on a slight slope surrounded by vinca minor, in soil that contains some rocks. The Wasatch Maple I planted seven years ago from a 5 gallon container is growing slowly in a dry garden, but is strong. It’s leaves can burn a little in a hot July, so maybe I will try a boost of mycorrhizae and a little more water in the summer. After talking to all these experts, I might suggest amending a dense clay soil with 10-20% expanded shale, wetting the roots when planting with mycorrhizae and covering the roots with a fine mulch. Keep it watered enough for the soil to be moist but not wet until established. It may be helpful to plant it where it gets shade from the late afternoon, since it is native in mountain canyons. It is probably better grown as an ornamental than as a shade tree. With its moderate to small size, tolerance to our alkaline soils and orange to red fall color, Bigtooth Maple could be a good replacement for that ash tree.