After 150 years, Arnold Arboretum has cracked the color code

There’s a world of fall hues on our doorstep.

Red, orange, deep green, and even purple hues make foliage season at the Arboretum a glut of intense color. David Lyon

‶I love all four seasons, even mud season at times. But there’s something special about autumn,″ says Michael S. Dosmann. ‶There’s nothing wrong with getting in the car and heading up to Vermont, New Hampshire, or Maine. But we have a few trees here in Boston that people can visit as well.″

Bearing the memorable title of Keeper of the Living Collections at the Arnold Arboretum, Dosmann knows of what he speaks. Now marking its 150th anniversary, the Arboretum preserves one of the planet’s most encyclopedic collections of trees and woody plants from temperate zones. It’s no stretch to say that autumn brings a world of color.

Officially the Arnold Arboretum of Harvard University, the 281-acre preserve is home to 16,000 trees, shrubs, and vines collected from all over the world — with a special focus on eastern North America and eastern Asia. The Arboretum may be an internationally acclaimed research facility, but it’s also a public park designed by Frederick Law Olmsted as part of the Emerald Necklace system. Free and open every day, this planned woodland just steps off the busy Arborway is a powerful antidote to the stress of urban life. A sage doctor might well write a prescription that reads, ‶Twenty-minute stroll on Arnold Arboretum paths. Repeat as needed.″

A panorama of orange and yellow greets walkers along Meadow Road at the Arboretum.David Lyon

The changing of the leaves in autumn might be the Arboretum’s headiest drug of all. “There’s a lot more plant diversity growing here than in the surrounding woodlands of New England,″ Dosmann points out. ‶With that, you have some things that come into autumn color a little earlier than the surrounding oaks and hickories and maples and others that extend a little later into the season.″

One of the Arboretum’s oldest specimens is the harbinger of fall foliage. The Schlesingeri red maple, propagated in the late 1800s from a tree spotted in a neighbor’s yard by Arboretum founding director Charles Sprague Sargent, is often the first tree to show fall colors. Just after the heat of August dog days, its leaves transition from grassy green to olive green. They soon begin to show deep red tones and reach full color in September. The original specimen is planted near the Arborway Gate, right across the road from the Hunnewell Visitor Center. It’s hard to miss.

We recognize that the planting system at the Arboretum follows a pretty specific taxonomic structure — almost a spreadsheet of temperate zone woody plants. But we’ve never approached walking in the Arboretum with anything like scientific rigor. We tend to wander at random. In the fall, we’re like small children in a toy store rushing from one bright and shiny thing to another.

Graceful forms of shrubs denuded of foliage lend a structural counterpoint to the bright blotches of the surrounding fall foliage.David Lyon

This year we plan to bring a little order to our visits. Dosmann recommends three fall strolling itineraries to take in the sweep of color. One of the best-modulated walks begins at the Arborway Gate between the visitor center and the Schlesingeri maple.

‶You have one of the best laid-out systems by Olmsted where you can really appreciate the curvilinearity of the roadways,″ he says. This route passes through several well-established tree collections, providing different canopies of shade.

One of the first stands contains the katsura trees, native to China and Japan. Their blue-green summer leaves tend to turn what Dosmann calls ‶pencil yellow.″Even more remarkable is the smell. As the leaves age, they produce a volatile substance called maltol, which smells a bit like burnt brown sugar.

Meandering paths originally laid out by Frederick Law Olmsted create a constantly changing vista of fall foliage at the Arboretum.David Lyon

‶I can’t count the number of times people thought there was a food truck around the corner or somebody was selling cinnamon rolls,″ Dosmann says. ‶It smells like a bakery.″

Keep walking along Meadow Road, passing the dawn redwoods (conifers that shed their needles every year) and you approach the icons of New England fall foliage: the maples.

‶When most people think of fall color, they think of sugar maples in particular,″ Dosmann says. ‶We have sugar maples, but we also have another 65 maple species collected from around the world. You’ll be able to see tremendous botanical diversity just within the maple genus. You have fall color of every shape and hue imaginable.″

At the southern end of the Arboretum, the Peters Hill loop walk brings you to one of the highest points in Boston. The summit provides an aerial overview of the foliage with hints of the Boston skyline in the distance. But don’t get too dazzled by the distant view.

‶When you’re strolling along Peters Hill, you can see all of the hawthorns and the crabapples,″ Dosmann says, noting that the fruits themselves are pretty colorful. The Peters Hill ring road is also home to one of the most important groves of ginkgo trees in the world. The tree is practically extinct in the wild, found only in remote spots in China. The Arboretum’s collection represents one of the world’s greatest arks of ginkgo genetic diversity. The tree’s distinctive fan-shaped leaves turn pure yellow in the fall. ‶When you suddenly see those ginkgos pop — wow! — it’s mesmerizing,″ Dosmann says.

Not everyone has several hours to meander through the Arboretum, though we can hardly think of a better way to spend an autumn morning or afternoon. For a quick loop of less than a half hour, Dosmann suggests Bussey Hill. Just below the summit, hard-to-grow plants thrive in the sheltered microclimate of the Explorers Garden. It’s home to the fall-blooming Franklin trees, now extinct in the wild. The large, white camellia-like flowers bloom from late August into September. The glossy dark green leaves then turn fire-engine red. Dosmann notes that sometimes the flowers and colorful foliage overlap.

A runner's bright turquoise top stands out from the warm tones of fall foliage at the Arboretum.David Lyon

He also points to the subtle attractions of the Seven Son Flower tree, another Explorers Garden denizen. When its fall flowers are spent, he says, ‶a few remnant portions of the flower have this pinkish mauve fireworks display that persists for a month or so. You’ll see those and a zillion other things up in the Explorers Garden.″

As the foliage season winds down, Bussey Hill is also a great spot to savor the subdued majesty of the final hurrah. ‶I love the hickory collection,″ Dosmann admits. ‶You have these tall trees that reach up to the heavens. You’re walking under a tall canopy of almost pure golden yellow.″

But be careful, Dosmann jokes. ‶Sometimes the squirrels intentionally try to dislodge the hickory nuts while you are directly underneath, just to frighten you out of their territory. You might get knocked in the head by a hickory nut, but it’s worth that gamble to experience the hickory collection in autumn.″

Hikers taking a less-traveled path at the Arboretum nearly disappear in the swirling colors of the foliage.David Lyon

If you go...

Arnold Arboretum of Harvard University

Hunnewell Visitor Center

Arborway Gate, 125 Arborway

617-524-1718, arboretum.harvard.edu

Landscape open sunrise-sunset; visitor center open Friday-Monday noon-4 p.m.

Free