Category Archives: Phenology

The Leaves Lingered

Though most trees are bare, the hilltop oaks still have leaves on 30 Nov 2021 (photo by Kate St. John)

4 December 2021

Last weekend many homeowners in Pennsylvania were annoyed that they had to rake leaves after Thanksgiving. A decade ago this would never have happened because the trees were bare by 5 November. Nowadays the leaves linger. Our warmer climate keeps them on the trees.

The delay in leaf drop has been increasing for at least a decade. In 2008-2012 most of the trees were bare by 2 or 4 November. In 2017-2021 the trees waited until 25-30 November. (*)

Meanwhile the height of fall color is later and lackluster. Twenty years ago we used to go leaf peeping on Columbus Day. This year the height of color in Schenley Park was on 13 November and not particularly breathtaking.

Fall color at Westinghouse Memorial in Schenley Park, 13 Nov 2021 (photo by Kate St. John)

Trees need a particular weather combination to trigger fall colors and leaf drop.

The timing and quality of color changes depend on a combination of temperatures, precipitation and sunlight. The best fall color displays occur after sunshine-filled days and cooler nights, following healthy doses of rain in the summer.

Washington Post: Fall foliage flopping: How climate change is dulling and delaying your leaf peeping

But it was way too warm in October. In fact it was the world’s fourth warmest on record.

U.S. Temperature Outlook for October 2021 issued 30 Sep 2021 by National Weather Service

The leaves lingered and finally by 30 November 2021 most of the trees were bare. Note that this date and all dates mentioned above are assessments of this same hillside in Schenley Park.

More than half of the trees are bare, Schenley Park, 25 Nov 2021 (photo by Kate St. John)

Read more about the disappointment of this fall’s foliage — and the economic impact — at the Washington Post: Fall foliage flopping: How climate change is dulling and delaying your leaf peeping.

(photos by Kate St. John, map from the National Weather Service)

Leaves and Merlins

Hornbeam seeds with spider/insect cocoons, 21 Nov 2021 (photo by Kate St. John)

27 November 2021

Nature was busy this week. Spiders or insects wove tiny white cocoons inside this hornbeam seed structure. Chickadees look for these cocoons and eat the tasty treats inside.

As predicted, Schenley Park’s gingkos lost all their leaves in a single day — 20 November.

Gingkos shed all their leaves on Schenley Drive, 20 Nov 2021 (photo by Kate St. John)

Norway maples were not far behind on the 24th.

Three trees on 24 Nov 2021: 1 bare, 2 maple fallen leaves, 3 red oak leaves waiting (photo by Kate St. John)

I went to Schenley Park golf course to find a merlin just before sunset on 23 November. Instead I found three merlins jostling for the highest perch on the highest hill. The tallest snag in this photo is not the highest perch but the dot on top is merlin #2 of 3 who is watching the airshow as 2,500 crows fly over from the Allegheny Valley to where? Crows were still passing overhead when I left.

After sunset the sky still glowed.

Cathedral of Learning, Heinz Chapel, and WQED’s transmission tower after sunset 23 Nov 2021, Pittsburgh, PA (photo by Kate St. John)

(photos by Kate St. John)

Fall Colors, Frost, and Bad Air

Colorful trees at Moraine State Park, 3 Nov 2021 (photo by Kate St. John)

8 November 2021

Last week began as a warm colorful autumn and ended with frosty mornings. This week begins with bad air.

Before last week’s frost I found splashes of fall color including this amaranth in an unusual place at Phipps Conservatory. Click here to see where this red plant was growing.

Amaranth in an unusual spot at Phipps Conservatory, 30 Oct 2021 (photo by Kate St. John)
Colorful leaves at Schenley Park, 30 Oct 2021 (photo by Kate St. John)

On 4 November the leaves glowed yellow as the sun gained altitude at Frick. When the sun melted the frost, leaves quickly loosened and dropped from the trees.

Sun through golden trees on a frosty morning at Frick Park, 4 Nov 2021 (photo by Kate St. John)

On Saturday morning at Yellow Creek State Park the frost was beautiful, ephemeral and cold. Hoarfrost decorated the weeds in the parking lot.

Hoarfrost on a grassy weed, Yellow Creek State Park, 6 Nov 2021, 9:39am (photo by Kate St. John)
Hoarfrost at Yellow Creek State Park, 6 Nov 2021, 9:39am (photo by Kate St. John)

Frost remained in a tree’s shadow but not for long.

Frost in the shadow, Yellow Creek State Park, 6 Nov 2021, 9:49am (photo by Kate St. John)

Last week I re-learned how to dress for winter. This week will be warm with highs in the 60s, lows in the 40s, temperature inversions and bad air in Pittsburgh.

Roger Day captured these views of the Mon Valley yesterday morning, 7 November, from Frick Park’s Riverview overlook. The Allegheny County Health Department has issued an air pollution warning and the state DEP has issued a Code Orange warning. Read more here.

Edgar Thompson Works in Braddock pouring smoke, seen through smog at Frick Park, morning of 7 Nov 2021 (photo by Roger Day)
Inversion: Edgar Thompson Works in the distance, Frick Park, morning of 7 Nov 2021 (photo by Roger Day)
Inversion: Kennywood seen through smog from Frick Park, morning of 7 Nov 2021 (photo by Roger Day)

Don’t breathe!

(photos by Kate St. John & Roger Day)

Pretty and Not

Bush honeysuckle fruit, Lower Nine Mile Run Trail, 23 Sep 2021 (photo by Kate St. John)

24 September 2021

In late September the most abundant fruits and flowers are often on invasive plants. Some are pretty, some are not.

Clusters of bright red berries look festive on bush honeysuckle (Lonicera tatarica) as they change from green to brown to red.

Porcelain berries (Ampelopsis glandulosa) are beautiful up close in turquoise and purple.

A few porcelain berry flowers are still in bloom.

But step back and the vine’s invasive habits are ugly as it drapes trees and hillsides. Yes, there are a couple of trees under the vine.

Meanwhile, in my opinion mugwort (Artemisia vulgaris) is unredeemable. In June it crowds the sunny edges of trails.

A thick stand of mugwort in June is not full height yet (photo by Kate St. John)

In September it’s tall and gangly with drooping green and brown stems. Are the brown bits seed pods?

No. They are ugly flowers.

Not pretty.

(photos by Kate St. John)

On The Beech

Beechdrops in bloom (photo from Wikimedia Commons)

23 September 2021

Tiny purple and white flowers are blooming this month on stems that stand a foot tall in the woods. Unless you know where to look for them, though, you’ll probably never see them. These brown plants match the ground.

Beechdrops (Epifagus virginiana) have no chlorophyll because they are parasitic on the roots of beech trees (Fagus grandifolia). To find the flowers, I find a beech tree(*) then put my head close to the ground and look sideways near the roots.

Look near the roots of beech trees for beechdrops (photo from Wikimedia Commons)

From this angle beechdrops stand out … barely.

Beechdrops (Epifagus virginiana) bloom from July to December, producing self-pollinating flowers at the base of the plant and cross-pollinating flowers at the top, though some of the top flowers are sterile.

The top flowers are pollinated by the winter ant (Prenolepis imparis) that aestivates underground when its hot and only comes out in cold weather. I imagine that’s why the July-blooming flowers are self-pollinating.

Beechdrops are so dependent on the American beech that their seeds don’t germinate until they detect a chemical signal from the tree.

Beech is really in their name. The genus Epifagus is Greek for epi = On + fagus = Beech.

On the Beech.

p.s. (*)Find a beech tree: American beeches have very smooth pale bark. See this blog post for tips on how to identify them: Winter Trees: American Beech.

(photos from Wikimedia Commons and Flickr Creative Commons license; click on the captions to see the originals)

Smart Weeds

Oriental lady’s thumb is an Asiatic smartweed, Schenley Park, 10 Sep 2021 (photo by Kate St. John)

13 September 2021

Today’s article began with a question asked three times: What is that weed? I couldn’t remember the name even though I knew each was in the knotweed family (Polygonaceae) and that a similar native species was named for Pennsylvania.

On the first question I took a picture in Schenley Park, above. On the second question, Claire Bauerle took a picture at Duff Park, below. My plant and Claire’s plant are both alien but not the same species.

Lady’s thumb (photo by Claire Bauerle)

Claire’s plant shows its name on its leaves, a shadowy thumbprint in the center of the leaf.

Lady’s thumb (Persicaria maculosa) is a Eurasian smartweed that first appeared in the Great Lakes region in 1843, has spread across the continent, and is sometimes invasive. The dark thumbprint is a simple way to identify the plant.

My plant is similar but lacks the thumbprint. Not the same species but my photo is not detailed enough for a complete identification. My guess is Oriental lady’s thumb (Persicaria longiseta) a common weed in Asian rice paddies introduced to North America near Philadelphia in 1910 and now found across eastern North America.

The third question was answered on Sunday’s Botanical Society walk on the South Side where we found the smartweed named for Pennsylvania.

Pinkweed or Pennsylvania smartweed (Persicaria pensylvanica) now grows in waste places around the world. Gangly-looking compared to the lady’s thumbs, it has longer stalks, thinner leaves, and fatter, shorter, paler flower heads.

Pinkweed or Pennsylvania smartweed mixed in with other weeds, 12 Sep 2021 (photo by Kate St. John)

Here’s a single stalk.

Pinkweed or Pennsylvania smartweed, 12 Sep 2021 (photo by Kate St. John)

It has no flower bristles like those found on Oriental lady’s thumb P. maculata.

Flower heads of pinkweed (photo by Kate St. John)

All three smartweeds have stems that connect to the stalks at knot-like ochreas. Two of them, P. longiseta and P. pensylvanicum have bristly ochreas, shown below.

Bristly ochrea on pinkweed, P. pensylvanicum (photo by Kate St. John)

Identifying smartweeds is much trickier than I’ve described so I may have misidentified the first two plants.

If I was smart I’d know what to look for and take better pictures to key them out.

(photos by Kate St. John and Claire Bauerle)

p.s. Three range maps which might not work in Chrome: P. maculosa, P. longiseta, P. pensylvanica

Fall Is Here

Misty walk at Panther Hollow Lake, Schenley Park, 10 Sep 2021 (photo by Kate St. John)

11 September 2021

The weather has been pleasant with low humidity and highs in the 70s. Chilly fall mornings produce a mist on Panther Hollow Lake.

Asters are blooming right on time …

Asters (photo by Kate St. John)

… but this hawthorn tree is confused, opening two flowers and a leaf in September.

Hawthorn tree puts out two flowers and a leaf, Schenley Park, 10 September 2021 (photo by Kate St. John)

This eastern screech-owl confirms it’s fall when he peeks from his well known roost on 4 September. Though screech-owls breed in Schenley Park, they only use this roost during the non-breeding season.

Eastern screech-owl at the winter roost, Schenley Park, 4 Sep 2021 (photo by Kate St. John)

My least favorite hot weather will return tomorrow through Tuesday, forewarned by this morning’s red sunrise.

Red sky at morn, sailors forewarn.

Sunrise in Oakland, Pittsburgh, 11 Sep 2021 (photo by Kate St. John)

(photos by Kate St. John)

Late July Flowers and Seeds

Oxeye or false sunflower, Nine Mile Run Trail, 29 July 2021 (photo by Kate St. John)

31 July 2021

In late July field flowers bloom while others develop seeds.

The photo at top of oxeye or false sunflowers (Heliopsis helianthoides) was supposed to be a documentation photo so I could study the leaves. Can you find the milkweed bug on one of the flowers?

Blue vervain (Verbena hastata) is blooming at Presque Isle State Park where I took this photo on Wednesday. Vervain flowers are so small that the plant looks boring from afar. It is well worth a closer look.

Blue Vervain, Presque Isle State Park, 28 July 2021

On Thursday Charity Kheshgi and I explored the grassland top of the slag heap at Nine Mile Run. In one area the slag is so porous that rainwater percolates straight though it, creating a desert habitat. Nonetheless we found a vibrant orange butterfly weed (Asclepias tuberosa) in bloom.

Butterfly weed at the slag heap, 29 July 2021 (photo by Kate St. John)

Namesake plant: Dwarf St. John’s wort (Hypericum mutilum) is native to North America.

Dwarf St. John’s wort, Moraine State Park, 30 July 2021 (photo by Kate St. John)

Seeds! Redbud trees (Cercis canadensis) in the city parks have a bumper crop of seed pods this year.

Redbud seed pods, thick on the branches, Nine Mile Run Trail, 29 July 2021 (photo by Kate St. John)

Nodding thistle (Carduus nutans) has gone to seed along the lower Nine Mile Run Trail where it looked like this in June (click here). We saw many American goldfinches feeding on these natural thistle feeders.

Nodding thistle seeds, Nine Mile Run Trail, 29 July 2021 (photo by Kate St. John)

Today is our last chance to enjoy July. The weather is lovely in Pittsburgh so get outdoors.

(photos by Kate St. John)

Blooming This Week in July

Nodding onion (Allium cernuum) at Phipps fence, 19 July 2021 (photo by Kate St. John)

24 July 2021

The weather came out of the northwest bringing cooler temperatures on Tuesday and Wednesday and smoke from the Canadian wildfires more than 1,000 miles away. Even when the air quality was bad this week I went outdoors. Perhaps I was fooled that it was OK since it didn’t have that sulfur smell typical of Pittsburgh pollution.

This week I went further afield than Schenley Park. Here are highlights from Frick, Schenley, Aspinwall Riverfront Park and Moraine State Park. The captions tell the story.

Horse nettle (Solanum carolinense), Frick Park, 20 July 2021 (photo by Kate St. John)
Black Snakeroot (Actaea racemosa or Cimicifuga racimosa) at Moraine State Park, 22 July 2021 (photo by Kate St. John)

Common mullein (Verbascum thapsus) has small flowers that we rarely see up close because they bloom on a six foot spike.

Common mullein inflorescence, Aspinwall Riverfront Park, 21 July 2021 (photo by Kate St. John)

We definitely notice the spike. And then the rest of the plant.

Common mullein, Aspinwall Riverfront Park, 21 July 2021 (photo by Kate St. John)

Meanwhile, my namesake plant is still blooming. This one was at Moraine State Park.

St. John’s wort (Hypericum sp.), Moraine State Park, 22 July 2021 (photo by Kate St. John)

(photos by Kate St. John)

Future Summers Will Last Half The Year

Hot summer sun (photo from Wikimedia Commons)

20 July 2021

Withering heat, parching drought, devastating floods, dangerous wildfires.

As unpleasant as this summer has been in the Northern Hemisphere we comfort ourselves that better weather will arrive with autumn in September. But even that is changing. A new study published in Geophysical Research Letters predicts that by the end of this century winter, spring and fall will retreat while summer will last nearly half the year.

For perspective on the future the researchers studied the past across the Northern Hemisphere, specifically the length of seasons from 1952 to 2011. They set the parameters for summer as the “onset of temperatures in the hottest 25% during that time period, while winter began with temperatures in the coldest 25%.” Spring and fall filled the gaps.

During those sixty years, summers got longer while the other seasons shrank. The slides below show the historical seasons 1952 and 2011 plus the study’s prediction for the year 2100. By then summer will run from May to October.

Average seasonal lengths in Northern Hemisphere, information from

For those of you who don’t like winter this sounds like a great idea but the reality will be unsettling. The long summers and short winters will continue to have extreme temperature and precipitation swings with stunning storms like those we’ve seen in recent years. Imagine the heat of July lasting three months or more.

Meanwhile pleasant days will become scarce. My favorite seasons, spring and fall, will be shorter.

Our great-grandchildren will live in a very different world.

Read more and see the large version of this animation at Northern hemisphere summers may last nearly half the year by 2100 at

(photo from Wikimedia Commons, simple pie charts by Kate St. John, embedded animation from