As autumn falls across the East Coast, the leaves begin to change color. Leaf-peeping season, though more popular farther north in New England, is an annual tradition in Pennsylvania that brings to mind apple cider doughnuts, plaid shirts, and cozy bonfires.

And Pennsylvania is a great place for it, thanks to the region’s deciduous forests. Maple leaves turn vivid red; ginkgo leaves turn bright yellow. Aspen, ash, and sumac trees each show their own shades.

“In North America, and especially in eastern North America, we are at the hot spot of the world in terms of having stunning red leaves in the fall,” explains Jake Grossman, a visiting assistant professor in the biology department of Swarthmore College and a visiting researcher at the Arnold Arboretum of Harvard University.

Why do leaves change color in the fall?

Grossman says that we still don’t totally know, though there are emerging theories. “It has been proposed recently that the red leaves are an adaptation to help plants deal with the long-term challenge of excess light in the fall,” he explained. Let’s get into the science.

In the fall, trees respond to colder temperatures and bright sunlight by sucking up as much nitrogen from the leaves as possible to conserve energy, taking with them chlorophyll, the compound that makes leaves green. Without that, other colors emerge.

Fall colors are split into two categories, because leaves turn yellow and orange for one reason, and red for a completely different one.

If the leaves turn yellow or orange, it’s because they contain compounds called xanthophylls, which protect against the harmful effects of too much light. Yellow and orange fall foliage can be found on a wide variety of trees in Pennsylvania, including ginkgos, lindens, elms, and bald cypresses.

Red leaves, on the other hand, are caused by the production of anthocyanins, which some scientists believe evolved specifically to protect plants from over-radiation. “We think of plants as loving light, but they actually are always balancing that against getting over-radiated with sunlight,” explained Grossman. The red color, as has been suggested, is a sort of sunscreen. Trees that have leaves that turn red in the fall in Pennsylvania include maples, red oaks, and black cherries.

When does fall foliage peak in Pennsylvania?

Peak foliage can be a moving target, made even more unpredictable by climate change. Over the last 50 years, peak foliage has moved later and later, sometimes extending longer as the leaves change more gradually.

When peak foliage happens, and what it looks like, will likely continue to change in the future. “With temperature increases, you normally see a dulling of all colors,” said Tanisha Williams, the David Burpee post-doctoral fellow in botany at Bucknell University in Union County. “If the days are really warm, trees may continue to produce chlorophyll, which are going to mask those colors; … we could basically miss a fall.”

According to Inquirer staff writer Anthony Wood, warm overnight temperatures are contributing to a slower-than-usual start to foliage season in the Pennsylvania region and up to Northeast states like New Hampshire and Vermont.

» READ MORE: Fall foliage in the Philly area may suffer from the unusually warm and wet weather

You can help track fall colors where you live by joining Nature’s Notebook, a website managed by the National Science Foundation, where you can contribute to data collection for scientists like Grossman.

These days, Pennsylvania sees peak foliage in mid- to late October. Because of the rainy summer we saw this year, Pennsylvania’s Department of Conservation and Natural Resources is predicting a particularly vibrant season, with peak foliage in mid-October. Each week, the DCNR releases a report with information about the status of foliage across the state. You can follow along on the DCNR’s website.

Whether your interest in fall foliage is scientific or you prefer to get taken in by the pure art of the fall landscape, here are some of the best places, in, around, and within a weekend’s trip of Philly for viewing fall foliage.

Where to see fall foliage in Philly

The Rodin Museum

The outdoor section of the Rodin Museum’s collection is a beautiful place to take in both fall foliage and the museum’s spectacular sculptures, which combine to create an experience unlike any other in the city. Although the museum is ticketed, the gardens are open to the public year-round and are speckled with linden and silverbell trees, which have leaves that turn a striking yellow in autumn.

📍2151 Benjamin Franklin Pkwy., 📞 215-763-8100, 🌐 rodinmuseum.org, 📷 @philamuseum

The Navy Yard

The Navy Yard received its Level I arboretum accreditation in 2018, achieved in partnership with the Pennsylvania Horticultural Society. The historic homes and buildings around the space are surrounded by similarly historic trees — visitors can enjoy the leaves of hundred-year-old sycamores, which turn bright orange and yellow, red oak, which turn bright red, and even sour gum trees, which turn a combination of orange, reddish, and even sometimes purple. These older trees form a nice backdrop for some of the more recently planted varietals. Walk along the Riverfront Greenway for the prettiest views.

📍4747 S. Broad St., 📞 215-843-9273, 🌐 navyyard.org, 📷 @navyyardphila

Laurel Hill Cemetery and West Laurel Hill Cemetery

Most people think of Laurel Hill and West Laurel Hill as historic cemeteries, but they are also an accredited arboretum, with many native and non-native trees. While both have fall foliage, arboretum manager Aaron Greenberg says the best colors are at West Laurel Hill, where visitors can enjoy long alleyways flanked by sugar maples, which are known for their bright red leaves, and by ginkgo trees, which have leaves that turn a distinctive yellow color then drop. Don’t worry, even if you miss the color, Greenberg says the carpet of leaves remains a seasonal wonder. For more professional guidance, join Greenberg on one of his annual foliage tours, scheduled this year for Oct. 24 and Nov. 7. Peak foliage is typically the end of October through the beginning of November, but follow their social media for updates.

📍3822 Ridge Ave., and 225 Belmont Ave. in Bala Cynwyd, 📞 215-228-8200 and 610-668-9900, 🌐 thelaurelhillcemetery.org and westlaurelhill.com, 🕐 April 1-Oct. 31, 7 a.m.-7 p.m., Nov. 1-March 31, 7 a.m.-5 p.m.

» READ MORE: A guide to historic cemeteries and graveyards in the Philadelphia region

Wissahickon Valley Park

The Wissahickon spans 1,800 acres in Northwest Philly and is one of the city’s most popular and accessible escapes into nature. The park has more than 50 miles of hiking trails, but for the best foliage, use the Lavender Trail to wind your way along an oak- and tulip tree-lined stream.

📍Valley Green Road, 📞 215-247-0417, 🌐 fow.org, 📷 @fowissahickon, 🕐 Daily, 6 a.m.-6 p.m.

Fairmount Park

For a new perspective on the leaves, visit Martin Puryear’s Pavilion in the Trees in West Fairmount Park, near Shofuso Japanese House and Garden. The elevated, covered deck gives you the opportunity to admire trees from among the branches, getting you up close and personal with the changing leaves.

📍Reservoir Drive, 📞 215-683-3600, 🌐 myphillypark.org, 📷 @myphillypark, 🕐 Daily, dawn-dusk

Awbury Arboretum

Start your visit to the Awbury Arboretum at the Francis Cope House, which is surrounded by old-growth trees, including a bright red maple that produce brilliant color. Then follow the Germantown arboretum’s self-guided heritage tree tour to see trees like a burnt-orange bald cypress, several American lindens, and an award-winning river birch. Admission is free but consider donating to support Awbury’s ongoing children’s programs and other community partnerships.

📍1 Awbury Rd., 📞 215-849-2855, 🌐 awbury.org, 📷 @awburyarboretum, 🕐 Daily, dawn-dusk

Bartram’s Garden

In addition to a famous Franklinia tree that William Bartram saved from extinction, the historic collection at Bartram’s Garden includes what is believed to be the oldest male ginkgo tree in North America, which offers bright yellow foliage in the fall, as well as the Bartram Oak, a hybrid of two types of oak trees that produces a variety of yellow to orange hues in the fall. The Bartram’s mile trail also offers a riverside view overlooking the city for a longer walk or short bike ride.

📍5400 Lindbergh Blvd., 📞 215-729-5281, 🌐 bartramsgarden.org, 📷 @Bartramsgarden, 🕐 Daily, dawn-dusk

Where to see fall foliage outside of Philly

Scott Arboretum of Swarthmore College

Scott Arboretum includes the campus of Swarthmore College, as well as the adjacent Crum Woods. Visitors can compare the color and timing of fall foliage on native trees like sugar maples, which turn red, with non-native, more exotic trees like the Norway maple, which turns yellow, says Grossman. The campus is open to the public for visitors who would like to visit independently, and the arboretum also organizes regular tours, including dedicated fall foliage tours starting in October. Find more information here.

📍500 College Ave., Swarthmore, 📞 610-328-8025, 🌐 scottarboretum.org, 📷 @scott_arboretum, 🕐 Daily, dawn-dusk

» READ MORE: Five fall hikes near Philly

Tyler Arboretum

The Tyler Arboretum has a diverse collection of curated trees, much like the one at the Scott Arboretum, ideal for comparing and contrasting native and non-native foliage, says Grossman. The difference is that Tyler also has 17 miles of hiking trails that go through 550 acres of wooded area, so you can take in both curated gardens and a natural forest. If you’re interested in more fall colors than just those on trees, check out the arboretum’s collection of late-season flowers, which bloom annually in the barn garden.

📍515 Painter Rd., Media, 📞 610-566-9134, 🌐 tylerarboretum.org, 📷 @tylerarboretum, 🕐 March-October, Mon.-Fri., 8 a.m.-6 p.m., Sat.-Sun., 8 a.m.-8 p.m., November-February, Mon.-Fri., 9 a.m.-4 p.m., Sat.-Sun., 9 a.m.-5 p.m., 🎫 $15 for adults, $13 for seniors, $9 for children, young adults, military and students, and free for children under 2

Valley Forge National Historical Park

Explore American Revolutionary history at Valley Forge by driving the 10-mile loop of the encampment, which includes stops at the visitors center, the National Memorial Arch, Washington’s Headquarters, and more, all while surrounded by beautiful autumn views. For the best foliage, though, hike to the peak of Mount Misery or Mount Joy, both of which offer broad vistas of the surrounding colorful fall foliage.

📍1400 N. Outer Line Dr., King of Prussia, 📞 610-783-1077, 🌐 nps.gov, 📷 @Valleyforgepark, 🕐 Daily, 7 a.m.-sunset

Washington Crossing State Park

Get up above the foliage for a bird’s-eye view at Bowman’s Hill Tower, which gives you views as far as 14 miles on a clear day. Or, take a kayak down the Delaware River surrounded on all sides by fall colors as part of the historic park’s Fall Foliage Float. The park’s naturalist will join the group to point out interesting trees and history.

📍1112 River Rd., Washington Crossing, 📞 215-493-4076, 🌐 washingtoncrossingpark.org, 📷 @washingtoncrossingpark, 🕐 Daily, 8 a.m.-8 p.m.

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Nockamixon State Park

In upper Bucks County, Nockamixon State Park offers more than 5,200 acres of protected land surrounding the lake — the largest in Southeastern Pennsylvania. Trees like maples, white oaks, and staghorn sumacs begin changing color in early October, and visitors can spend a day hiking, biking, kayaking or even horseback riding, while those needing a bit more nature can rent a (heated) cabin or reserve a campsite for an overnight stay.

📍1542 Mountain View Dr., Quakertown, 📞 215-529-7300, 🌐 dcnr.state.pa.us, 🕐 Daily, sunrise-sunset

Ridley Creek State Park

In addition to natural landscapes and striking waterfalls, Ridley Creek hosts formal gardens around its visitors center. Take a walk past the Hunting Hill Mansion, an English-style country manor built in 1789, which, when surrounded by changing fall foliage, has a haunting atmosphere that feels seasonally appropriate.

📍1023 Sycamore Mills Rd., Media, 📞 610-892-3900, 🌐 dcnr.state.pa.us, 🕐 Daily, sunrise-sunset

Jim Thorpe, Pa.

The Pocono Mountain town of Jim Thorpe celebrates the season with its annual Fall Foliage Festival. This year’s, which will take over the historic town each weekend from Oct. 9 through 24, features live music, street food stalls, and rides on the Lehigh Gorge Scenic Railway, which takes a 16-mile loop along the Lehigh River and into Lehigh Gorge State Park, with scenic views of foliage the whole way. Those seeking outdoor adventure can opt to ride the train to White Haven, Pa., then return by bike on a 25-mile, downhill ride through car-free, tree-lined trails. Jim Thorpe also sits at the base of Mount Pisgah, a 2,260-foot summit which offers views from above or below. Keep an eye out for peak foliage with the Pocono Mountains Live Cameras, one of which looks over the town.

🌐 jimthorpe.org, 📷 @visitjimthorpepa

Bald Eagle State Forest

Bald Eagle State Forest makes up close to 200,000 acres and more than 300 miles of trail acres in Central Pennsylvania, encompassing several swaths of old-growth forests that show off intense color in the fall. The variation in elevation — from the Susquehanna Valley to the Allegheny Mountains — creates variety in the type and intensity of foliage and offers several higher-altitude overlooks for seeing the patchwork of color created by the fall foliage.

🌐 dcnr.pa.gov

Promised Land State Park

The forests at Promised Land are made up of many maple, cherry, birch, beech, and oak trees, providing a cacophony of bright reds, golds, yellows, and oranges. The two lakes in the park make the color that much more compelling — take in the reflection from the water by renting a kayak, canoe, or peddle boat at Promised Land Boat Rental. Campsites and rustic cabins are available for overnight stays.

🌐 dcnr.pa.gov

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