Pardon the Interruption…

Can a garden plant connect us to a past so unimaginably distant that Earth itself was unrecognizable?

If we interrupt our routines, just for a moment, we can consider a plant that links us to an ancient time. Osmunda claytoniana, commonly known as “Interrupted Fern,” looks perfectly at home in a modern garden, yet it is essentially the same plant it was over 200 million years ago! Even before the first T-rex appeared, Interrupted Fern inhabited lush woodlands on proto-continents that later splintered, collided, and drifted apart.

A fossil found in Antarctica tells the story. In the late Triassic period (252-201 million years ago), the land mass that is now Antarctica had a temperate climate. There, growing near a stream in a shady forest, an Interrupted Fern became encased in sediment and then fossilized. The fossil reveals a plant that is virtually indistinguishable from Interrupted Ferns growing in gardens and forests in the Northeastern US today! Most plant and animal species found on Earth in the Triassic became extinct millions of years ago. Of those that survived, most have undergone so many mutations and evolutionary changes that they are virtually unrecognizable. But Interrupted Fern has continued – essentially without interruption!

Osmunda claytoniana is called “Interrupted Fern” because of its unusual and readily-identifiable structure. While most ferns carry their spores on separate stems or on the undersides of leaves, Interrupted Fern sends up fertile spore-bearing fronds from the center of the plant with feather-like clusters of “sporangia” in mid-stem. As the spore clusters ripen and drop away, the mid-section of the frond is “interrupted” leaving bare space between the leaves.

Spore-producing structures interrupt the leaves on fertile fronds
Close-up of spore-bearing sections
As spores mature, they dry up and drop away
The fertile fronds are left “interrupted” between leafy sections

Interrupted Fern is a great landscape plant. It emerges in early spring and remains fresh and upright throughout the summer, making an architectural statement in the garden. The fronds typically reach about 3 feet in height, and form an attractive vase shape. The fern expands its territory from the rhizome slowly, over a decade or so, eventually forming a clump. Once established, a clump of Interrupted Fern can be very long-lived. Thriving examples have been found in gardens abandoned for over fifty years. A colony of a naturally-occurring hybrid between Interrupted Fern and its close relative, Royal Fern, in Virginia is thought to be about 1,100 years old.

A 30-year-old clump of Interrupted Ferns looks great under mature trees along a driveway in suburban New York

Though it once lived in Antarctica, Interrupted Fern is found today only in Eastern and Central US and Canada. It does best in rich, moderately damp acid soil in full to part shade, but it grows taller (4-5 feet!) with more sun. Hardy in Zones 3 to 7, it is not palatable to deer – or dinosaurs, apparently. It provides cover to small birds and mammals, and makes an excellent underplanting for trees, especially at the edges of wooded areas where leaves are allowed to remain in place, enriching the soil.

Osmunda emerging in spring

Interrupted Fern dies back to the ground in late fall, leaving a mounded crown at the surface of the soil and a network of fine roots below. The rhizome can be dug for transplanting with a sharp spade in early spring by cutting the roots 4 to 6 inches from the crown and settling the crown in the new spot at the same height, spreading the roots out under a light layer of soil. Leaf mulch or compost are much better than bark mulch for keeping the soil moist and cool. In spring, the fronds emerge covered with long, fuzzy hairs and unfurl over a week or so. Once established in a suitable spot, Interrupted Fern really needs nothing more from humans!

From dinosaurs to automobiles, a living fossil in the modern world

As we worry about climate change, destruction of habitat, and the alarming loss of plant and animal species in what scientists are calling the “Sixth Great Extinction,” there is some comfort in observing this lovely plant that has seen more than one apocalypse and managed to survive unchanged. This ancient fern may just survive it all.

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A Perennial Star

It won’t be long now…the show is about to start! 

Each spring, excitement builds as Eastern Bluestar (Amsonia tabernaemontana) breaks ground and gets ready for its performance, which happens in three acts! Amsonia is a 3-season performer. From May through November, this native plant is a star.

Eastern Bluestar emerging in May

The overture starts in mid-spring when shiny green leaves emerge wrapped around deep blue flower buds. The buds ride along as the leafy stalks rise to a height of 30 to 40 inches. Soon, the real show begins as the pale blue stars that give the plant its common name open, attracting a huge variety of pollinators.

The flowers rise with the growing stalks
 Pale blue stars cover the plant by late May

The second act lasts all summer long – four full months! Amsonia is a clump-forming perennial that functions almost like a shrub. In time, the plant expands slowly from the base, but does not spread easily either by rhizomes or seed. The glossy foliage looks fresh all summer, reaching about 3 feet tall and almost as wide, and mixes well in a garden border, or even in a meadow planting. The stems may be cut back a bit after flowering to keep the plant’s compact form, or allowed to arch out in a looser shape.

Amsonia tabernaemontana at the New York Botanical Garden paired with Zizia aurea for a dazzling native combo
 Amsonia in the foreground with meadow plants in mid-summer

In Act Three, Amsonia turns bright yellow, and the fall color lasts for weeks! It looks great combined with evergreens and fall berries, or mixed with contrasting foliage colors. The plant goes dormant and dies back to the ground in winter after 7 months of extraordinary performance.

In November, Amsonia’s brilliant yellow contrasts with the purple foliage of Ninebark (Physocarpus opulifolius) at the Nature Center

Native to moist woodland edges, and along streams and ponds from New York to Florida and west to Texas and Illinois, Eastern Bluestar is happy in Zones 3 through 9. Though its natural habitats are moist areas with well-drained soil, it is quite drought tolerant once it is established, and is reported to tolerate clay as well. It prefers full sun in the northern part of its range, but appreciates some afternoon shade in warmer regions. 

Young plants may take a few seasons to get established, but Amsonia is a long-lived perennial. After a few years, the base of the plant becomes quite woody and difficult to divide, but left alone, it comes back year after year for a decade or more. And Amsonia is pest resistant – it has white latex sap that deer and other critters avoid. Gardeners with latex allergies may also wish to avoid it by wearing gloves. 

It’s surprising that Eastern Bluestar isn’t better known among today’s gardeners since even its name dates back to Colonial times. Amsonia was named for a physician and amateur botanist, John Amson, who lived in Williamsburg, Virginia and once had a very famous patient. In 1758, George Washington was worried that he had contracted “consumption” (tuberculosis) during the French and Indian War. Fearing the worst, he visited Dr. Amson for advice. The good doctor reassured General Washington that he had nothing more than a common cold and was not going to die. To honor the esteemed Dr. Amson, the botanist John Clayton named the perennial flower “Amsonia” shortly thereafter.

If you go shopping for Amsonia tabernaemontana, you are likely to run into a few other Amsonias, and there can be some confusion here. A variety called Amsonia tabernaemontana var. salicifolia is native to the southeastern U.S. and has slightly narrower leaves than the northern species. It is often sold in nurseries in the Northeast, and is difficult to distinguish unless they are viewed side-by-side. There is no particular reason to avoid salicifolia unless you are in the Northeast and trying to plant strictly local native species.

Amsonia ‘Blue Ice’ with taller Eastern Bluestar in the background

A more perplexing issue is presented by Amsonia ‘Blue Ice,’ which is being widely sold and is becoming increasingly popular. A few years ago, a commercial grower with a greenhouse full of Amsonia tabernaemontana noticed some plants in the crowd with slightly larger and darker blue flowers and foliage more compact than the species. Horticulturists first classed ‘Blue Ice’ as a “selection,” a naturally-occurring variation with desirable characteristics that is then cultivated for sale by stem cuttings. Further study, however, has suggested that ‘Blue Ice’ is of “uncertain parentage,” which sounds a bit scandalous and could mean that ‘Blue Ice’ is a hybrid or an accidental introduction or something else altogether. At present, although the genetic mystery rules out the plant for purists, it really is a lovely garden perennial. ‘Blue Ice’ stays under 2 feet tall, which is great in smaller gardens.

Amsonia hubrichtii

There is another popular species of Amsonia called Amsonia hubrichtii or Threadleaf Bluestar, which is native only to Arkansas and Oklahoma. Although it is a fine garden plant, and is regularly sold outside its native range, you will maximize ecological benefits in your own area by planting the species that is native there. 

For most of the Eastern US, and much of the Southcentral US, Amsonia tabernaemontana, our own Eastern Bluestar, is the true perennial star. Let the show begin!

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After the Deluge

If you’ve ever enjoyed the sight of rain drops clinging to every leaf of a tree after a storm, you have observed one of the ways trees manage stormwater. 

Forests intercept rainwater in the tree canopy, and slow its fall to the forest floor where it is absorbed and filtered before any excess gradually moves to streams. A forest can absorb at least 12 inches of precipitation per hour before surface water begins to move toward natural channels. In urban and suburban areas, with limited tree canopy, heavy rainfall hits the ground immediately and accumulates on impermeable surfaces, causing flooding.

Frequent flooding makes stormwater management a top priority

As rainstorms increase in frequency and intensity, flooded roads, neighborhoods, and basements have become critical problems for municipalities and residents. Storm water run-off from impermeable surfaces too often exceeds the capacity of urban and suburban systems. Engineered solutions to flood control are complicated, expensive, and controversial, so urban planners are increasingly considering “green infrastructure” – essentially, managing stormwater by changing how we landscape.

Trees not only remove carbon dioxide from the atmosphere, feed and shelter wildlife, and reduce energy demand for cooling, they are also the most cost-effective way to manage stormwater. Trees and related landscaping can keep excess water off of roadways, and out of your basement.

Trees manage stormwater in several critical ways. If you’ve ever sheltered from rain by moving under a tree, you’ve experienced “interception.” The tree canopy catches rain and holds raindrops on every leaf, twig, stem, and branch until they evaporate after the storm. A mature evergreen can intercept more than 4,000 gallons of rainwater in a year. In a suburban setting, a single deciduous tree intercepts 500 to 760 gallons per year. And a recent experiment demonstrated that even a small flowering tree can intercept 58 gallons of storm water during a ½ inch rain event, or about 67% of the rain that falls on its canopy. Intercepted stormwater never even touches the ground, so it cannot become run-off or cause flooding.

Interception: even in winter, bare tree branches intercept stormwater and hold it for evaporation
The heavily-textured trunks of mature trees slow water down as it falls (“stemflow”) and hold rain until it evaporates

Rainwater that is not intercepted by the canopy and hits the ground is called “throughfall.” Tree roots, which typically spread at least as wide as the tree canopy and are concentrated in the top 18 to 24 inches of soil, break up compacted soil so that more throughfall infiltrates and is absorbed by the ground. Ground water is then taken up by tree roots, transported to the leaves, and used in photosynthesis. That water ultimately is released back into the atmosphere in a process called “evapotranspiration.”

Tree roots absorb water directly and also make soil more absorbent

Trees consume or “transpire” an enormous amount of water. A single mature oak tree can transpire more than 40,000 gallons of water per year! Homeowners who take down mature trees may be shocked to realize that all of that water becomes run-off and a source of flooding when the tree is gone. 

A tree surrounded by pavement or lawn takes up less water than a tree in the forest or a tree accompanied by other plants. Leaf litter, groundcovers, and understory plants dramatically increase the ability of the soil to absorb stormwater. By increasing organic matter and leaf surface under trees, both the amount of stormwater held, and the amount available to the tree for evapotranspiration, are increased significantly.

By contrast, lawn grass is barely more effective than pavement at reducing stormwater run-off. The roots of turf grass are only about 2 inches deep and do not retain much water. Mowing, removing lawn clippings, and using leaf blowers all have the effect of compacting lawn and reducing organic matter in the soil, further reducing its ability to take up water. Automatic irrigation systems, programmed to top-water lawn every couple of days without regard to rainfall, add to run-off problems.

Lawn grass is not effective for stormwater control
The force of stormwater run-off on lawn is even enough to erode paving

Worse, in most communities, storm drains do not channel run-off into sewage treatment facilities, but directly into local waterways, so the chemical fertilizers and pesticides typically applied to lawns are transported by stormwater run-off to our waterways. Pesticides, applied to lawn annually at 10 times the rate used by farmers, are a leading source of water pollution, contaminating groundwater, freshwater streams, rivers, and coastal waters. Lawn fertilizer, washed into storm drains, causes algae blooms and excessive weed growth in waterways.

Storm drains route stormwater directly into streams, rivers, lakes, and the ocean
Stormwater run-off carries toxic pesticides from lawns

Suburban residents can make their yards into “green infrastructure” by reducing lawn and planting densely with native trees and other plants. Parking lots, road medians, church and school grounds, apartment complexes, and any place with lawn or paved surfaces can be added to green infrastructure by planting native trees and landscape plants wherever possible. The best way to prevent stormwater run-off from flooding your basement, blocking your street, and reaching our rivers is to capture it in your own yard with the beautiful trees and plants native to our area.

Dense planting reduces stormwater run-off on a suburban driveway

Seasons in the Meadow

Meadows change. All landscapes change, of course, even the most formal manicured gardens. But native plant meadows are wilder, less predictable. Nature has a freer hand where plants are allowed and expected to reproduce naturally, and where humans impose less control over conditions. In each season since the initial planting of our native Meadow (see last week’s blog post here), we have been surprised, sometimes frustrated, and always fascinated by the changes we see. Our challenge is to accept as many of nature’s changes as we can, while preserving the value of the Meadow for nature itself.

In the Northeastern US, which was once almost entirely forest, naturally-occurring meadows are typically “successional.” They occur when a storm or fire opens a spot in the forest and more sunlight allows grasses and wildflowers to emerge. Eventually, woody shrubs and tree seedlings settle in, grow taller, cast shade, and the forest returns. Unfortunately, in modern times, any newly opened ground is immediately colonized by invasive species, plants from other parts of the world that out-compete native plants because they have no natural insect or animal controls here.

So, maintaining a designed meadow in the Northeastern US requires effort to prevent invasive plants or forest from claiming the space. The incredible value of a native meadow as habitat for insects, birds, reptiles, and mammals makes that effort totally worthwhile. 

Guy Pardee of Suburban Natives, LLC mowing the Meadow in early April

We begin each year in the Meadow by mowing to prevent tree seedlings from developing, and to allow sun and water to reach new growth. The timing of mowing is important. We need to wait for over-wintering insects, including native bees and caterpillars, to emerge from their hiding places in leaves and hollow stems, usually in late March or early April. The Meadow is cut to the ground, leaving plant debris in place to add nutrition to the soil and to protect emerging growth from late frosts.

Seedlings of White Pine, sumac, and birch appear every spring, trying to re-forest our Meadow
Plant debris is left on the ground after mowing

Spring mowing also allows us to check the Butterfly Arbor and the trees in the Oak Circle for any winter damage. And it’s a good time to look for and remove invasive species before they can hide among the native plants.

Ivy trying to invade the Meadow

A few weeks after mowing, when the first spring flowers emerge, we see that the Meadow has changed again. Each year there are surprises, and occasional disappointments, as plants appear and disappear. We are delighted when native plants volunteer in places they were never planted – a true indication of a healthy landscape! And, sometimes, we notice that flowers we love have disappeared as they reach the end of their life expectancies, or lose ground to stronger plants.

Whorled loosestrife, Wild Sarsaparilla, and Appalachian Sedge are native plants that volunteered at the Meadow edge
Prairie Smoke, a spring bloomer, sadly disappeared from the Meadow after a few years
Photo: Travis Brady

By June, the Meadow is in full bloom. Coreopsis, Penstemon, Baptisia, and many other flowers greet visitors — including butterflies, bees, and countless other pollinators! 

Baptisia blooms in early June
Penstemon and Coreopsis in mid-June

Throughout the summer, the Meadow continues to change – not just seasonal changes, but changes in plant populations. Years after the original seeding, plants have appeared and bloomed for the first time as slow-growing seeds finally matured. And the number and location of plants in the Meadow changes every year.

An uncommon plant, Castilleja coccinea, was included in the original seed mix planted in 2014, but only appeared and bloomed for the first time in June 2021
Joe Pye Weed was not a big presence in the early years of the Meadow, but after one rainy summer, it became prolific

Throughout the growing season, some weeding is necessary to keep invasive plants out of the Meadow. Even some native plants are too aggressive to leave uncontrolled, or they would soon dominate. We make careful edits, avoiding use of herbicide, and quickly fill in weeded areas with container-grown native plants. 

Canada goldenrod is a beautiful native plant, but can out-compete everything else, so we cut it back before it goes to seed

Autumn is the most dramatic season in the Meadow. Late-blooming flowers and grasses change the scene daily with a profusion of color. Seed pods from faded flowers attract songbirds in large numbers, and bees scramble to stock up for winter.

Early September on the Arbor path
Late September flowers
Bumblebee on Echinacea
Switch grass in October
Milkweed seed pod
Photo: Travis Brady
Late October view of the Butterfly Arbor

Meadow plants are left standing all winter to provide seeds for birds, cover for animals, and winter hiding places for insects. There is a lesson here for all of us as home gardeners: a little mess, a little bit of wild in the landscape, can be as beautiful as it is beneficial for living things.

As the light changes with the seasons, the Meadow changes, too. It really is a different place each time we visit!


How We Made a Meadow

It was a weed-infested patch of land just steps away from the busiest commercial corridor in Greenburgh. A little less than 2 acres, it had been neglected for decades. But it was flat, sunny, dry, and open. Perfect for a meadow!

 Overwhelmed with invasive weeds
Meadow site cleared

After an initial clearing, we got a better look. There were some nice native birch trees, an ancient stand of bayberry, and several old apple trees remaining from what had once been an apple orchard. 

We were very lucky to meet a talented landscape architect who offered to donate his design services to the Nature Center. Bill Boyce of Biosphere Landscape Architects brought his expertise in natural landscape restoration to the project. He designed a space that would retain the best features of the site, while adding places for education and contemplation. Our guiding principle was to create and preserve a diverse habitat of native plants for insects, birds, and other animals.

Bill Boyce of BiosphereLA
Bill’s design plan

We knew that the most natural look for the meadow would require planting from seed, carefully selected for site conditions, using a large variety of native wildflowers and grasses. For that, we turned to Larry Weaner of Larry Weaner Design, the foremost authority in the Northeastern US on designing and planting native meadows. Larry formulates custom seed mixes using a complex formula based on seed germination rates, aggressiveness of various species, length of time each species takes to germinate and establish roots, and many other factors. Like Bill, Larry was kind enough to contribute his time and expertise for the Nature Center’s meadow project. 

Larry Weaner, expert on meadow design and planting

In December of 2014, we cleared the site again, much more thoroughly, removing as many roots of the weedy invasive species as possible, but leaving a few valuable native plants. Bill marked off the areas to be seeded, and we carefully hand-cast Larry’s specially-formulated seed mix.

Final thorough clearing and marked off planting areas
Hand casting seed in the new meadow before rolling to press seed into bare soil
Bill Boyce, Cathy Ludden, Larry Weaner, and Travis Brady did the final clearing and hand-seeding in December 2014

Bill’s design included an Oak Circle, which we hoped would become a calm space for meditation, as well as contribute the immense ecological value of native oak trees. Bill also designed a Stone Classroom, where our staff naturalists could work with students on-site in the meadow.

Newly-planted Oak Circle
The Stone Classroom

It takes at least 3 years for a seeded meadow to establish. Soon after plants emerge in the first spring, the meadow is mowed to about 6 inches in height. The idea is to cut back returning invasive species, which grow faster, giving the native seeds time to germinate without being overwhelmed. Two additional mowings the first summer, at increasing heights, keep invasive weeds under control as the new native plants develop roots.

First season meadow is kept short to allow new seeds to germinate, Spring 2015

In the second season, the meadow is mown once in the spring, and once more in mid-summer. The third year, the meadow is mown only once in the spring, as it will be annually thereafter.

Baby native plants appear in the meadow

In the winter of 2016, Bill Boyce constructed our Butterfly Arbor, taking his design inspiration from the wings of a Monarch Butterfly. He allowed native sumac shrubs to remain near the Arbor to soften the edges of the design.

The new Butterfly Arbor in April 2016
Design inspiration

The Arbor has removable doors and is specially designed to allow netting to be suspended inside for our annual butterfly exhibit

Preparing for the butterfly exhibit, Spring 2016

The native plant meadow at the Nature Center is now 8 years old. It has matured, but it still changes each year and in every season. It has become the very special place we hoped it would be. It is filled with life and beauty.

Monarch visits Swamp Milkweed
A diverse array of wildflowers

The meadow is a wonderful place for education and contemplation.

The Stone Classroom in use
The Oak Circle is a peaceful spot

The meadow is a joyful place to explore for people of all ages.

Next week in Around the Grounds we will discuss meadow maintenance and how changing seasons affect the meadow.