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March 17, 2022February 14, 2025 Cathy Ludden Around the Grounds, Native Plants

The All-American Shamrock

Legend tells us that St. Patrick used a shamrock, with its three leaves on a single stem, to teach ancient Celtic peoples about the Christian trinity. There is no agreement among historians, theologians, or botanists, however, as to which specific plant is the legendary Irish shamrock.

Some believe St. Patrick’s shamrock was one of several species of clover (Trifolium spp.) native to Europe and Britain. Others claim that the true Irish shamrock is in the family Oxalis, perhaps due to a report from a 16^th Century Englishman who wrote that the Irish ate “shamrocks,” and plants in the Oxalis family were known to be edible. Adding to the confusion, the Irish word “seamróg” means “little clover.”

Today, in honor of St. Patrick’s Day, several Oxalis species are sold as shamrocks both here and in Europe, which just annoys those who insist the traditional shamrock is a clover. In 1988, someone conducted a public opinion poll in Ireland asking which plant is the true shamrock, and the results split among several plants, including two varieties of clover and at least one Oxalis, with no real majority view.

In any case, St. Patrick’s Day seems an appropriate time to nominate an American native plant as the New World shamrock. Yellow Wood Sorrel (Oxalis stricta) is sometimes called “sourgrass,” “pickle plant,” or adding to the general confusion, “lemon clover.” As a candidate for St. Patrick’s Day shamrock, Yellow Wood Sorrel certainly looks the part.

**Yellow Wood Sorrel in bloom***Photo: Ansel Oomen, Bugwood.org*

Yellow Wood Sorrel is useful, maybe even pretty if you look closely, and it is found absolutely everywhere. Yes, it is a weed! You’ve probably pulled it out of your lawn, your garden, your containers, your driveway or sidewalk — maybe without knowing or caring what it is.

Like many other weeds, Yellow Wood Sorrel grows in a wide variety of habitats – sun or shade, dry or wet, and rich or poor soil. Each of its 3 leaves has a fold down the middle. At dusk, the leaves close up and stay that way until warmed again by the sun.

The little yellow flowers have 5 petals and bloom from spring through late fall. The plant produces lots of seeds in capsules that stand upright above the foliage. When the seeds are ripe, the capsule explodes, throwing seeds up to 3 feet away!

*Oxalis stricta* leaves fold up at night like little pleated skirts
*Photo: Courtesy of Pixabay.com*

Yellow Wood Sorrel is edible, though in very large quantities it may be mildly toxic. You really should try clipping some tender leaves, or the little yellow flowers, and sprinkling them like micro-greens on top of salads, fish, or chicken. The taste is like lemon, sour and a bit bitter, but refreshing. Tender stems and leaves may be steeped in hot water (a handful of leaves per pint of water) to make a lemonade-type drink high in Vitamin C.

Bees, butterflies, and ants make use of the flowers of Yellow Wood Sorrel, and its long season of bloom means the flowers are available throughout the nectaring season. Perhaps we should be grateful that this weed provides some wildlife benefit by stubbornly popping up in even the most manicured suburban landscapes.

**Yellow Wood Sorrel is a small weedy plant that grows everywhere**
*Photo: T. Webster, USDA, Bugwood.org*

So, the next time you find yourself pulling Yellow Wood Sorrel from all the places it doesn’t belong, think of it as shamrock and then save a few leaves for your lunch. Sláinte!

THIS BLOG IS AUTHORED WEEKLY BY CATHY LUDDEN, CONSERVATIONIST AND NATIVE PLANT EDUCATOR; AND BOARD MEMBER, GREENBURGH NATURE CENTER. FOLLOW CATHY ON INSTAGRAM FOR MORE PHOTOS AND GARDENING TIPS @CATHYLUDDEN.

February 17, 2022February 14, 2025 Cathy Ludden Around the Grounds, Invasives

Evil Ivy Over Everything

We have a big problem at the Nature Center. And we are not alone.

Ivy (Hedera spp.) – English Ivy, Irish Ivy, Persian Ivy – causes enormous damage to trees, buildings, and forest ecology throughout the United States. Maybe you’ve already seen Ivy pull stucco, mortar, trellises, and rain gutters off of buildings, or cause wooden siding to rot or attract mold. At least those things can be repaired.

The damage Ivy causes in nature is much worse. It climbs trees, slowly strangling them to death by stealing light and water, and it weighs down their weakened branches until they break and fall during storms. It crawls across the ground, sending out roots to take up all available nutrition. And it smothers the ground with its evergreen leaves so other plants cannot establish or find enough light to survive.

Ivy chokes trees by stealing light, air, and water

The weight of ivy breaks trees already weakened by choking vines

Forests in our region were once populated with hundreds of different species of shade-loving plants: ferns, grasses, and a huge variety of wildflowers. Those plants fed thousands of species of insects, birds, and animals. Of course, development and too many deer have contributed to a tragic loss of these species, and so has the introduction of invasive plants. Ivy is one of the worst offenders.

A healthy forest is filled with great diversity of plants

Ivy eliminates other species on the forest floor

There is nothing wrong with English Ivy — in England! It doesn’t overrun woodlands in Europe because it evolved there, and European insects and animals eat Ivy and control its growth.

In America, there are no natural controls, no insects or other animals to keep it in check, so Ivy becomes invasive. It out-competes native plants, leaving the forest depleted and sterile. Nothing here eats Ivy, so when Ivy is all that is left in the forest, there is nothing for forest animals to eat.

Some birds eat berries produced by Ivy and scatter the seeds, which can spread Ivy from garden to forest. But humans are much more culpable. Ivy is unfortunately popular with humans because it is evergreen, grows very fast, will live in sun or shade, and can cover a lot of ground or a wall very quickly. But it is also very difficult to control once it is established. Cutting vines at the base, applying herbicide to cut stems, and digging out roots can help save trees, but diligence is required to prevent this very aggressive pest from trying again.

There is no true Ivy native to North America. But there is a beautiful native plant that makes a great substitute for Ivy. If you want a climbing vine to cover a wall or an arbor, or you’re looking for a groundcover for a shady area, try Virginia Creeper (Parthenocissus quinquefolia). It is fast growing, and it has glorious fall color. Its leaves are the host plant for the very interesting Sphinx moth – the native insect that acts as a natural control preventing this vine from taking over the forest. Virginia Creeper will wind its way up a tree trunk, but it won’t kill your trees.

Virginia creeper evolved here, and belongs in our woods – *photo courtesy of pixabay.com*

Don’t be confused by the common names of Boston Ivy (Parthenocissus tricuspidata) and Poison Ivy (Toxicodendron radicans). Boston ivy is not from Boston and it’s not an Ivy. It is an Asian vine in the same family as Virginia Creeper. Though it is not as destructive as Ivy, it actually can grow faster and taller than Ivy and completely cover a building in no time. Poison Ivy is not an Ivy either. It is a native vine and, interestingly, it is only “poison” to allergic humans and not at all to other animals. It actually has a lot of wildlife value to birds and other animals. If it’s not in your immediate area, you could consider admiring its beautiful fall color from afar!

In the coming years, the Nature Center has a fight on its hands. We want to remove Ivy from our 33 acres of woods. While some areas are only partially affected, and we work hard to keep Ivy off of our trees, there are large sections of our forest totally overrun with Ivy. We will be formulating plans for an Ivy-removal program this year, but it will be difficult and expensive. If you would like to help by making a contribution, please visit our Donate page here.

This blog is authored weekly by Cathy Ludden, conservationist and native plant educator; and Board Member, Greenburgh Nature Center. Follow Cathy on Instagram for more photos and gardening tips @cathyludden.

February 10, 2022February 14, 2025 Cathy Ludden Around the Grounds, Native Plants

Forever Green: Native Groundcovers That Stay All Winter

Given our recent weather, you may well ask, “why should I care whether a ground cover is green if it’s under a foot of snow”? Fair question!

In our milder winters, when snow comes and goes, evergreen groundcovers do offer structure and winter interest in the garden. And they benefit birds and small mammals, providing cover from predators and shelter from icy winds. But not so with ivy or pachysandra! Both are invasive, non-native plants that must be prevented from running into wooded areas where they smother everything! Fortunately, there are native evergreen groundcovers much better suited to our landscapes and helpful, rather than harmful, to the ecosystem.

We recently described Leucothoe, a native evergreen that can replace pachysandra as a ground cover under trees and shrubs and in wooded areas.

Another evergreen woodland plant we love is Christmas fern (Polystichum acrostichoides). Not truly a groundcover, because it stays in place rather than spreading itself around, Christmas fern can be planted densely to fill in a shady area. Deer won’t eat it, and it’s such a pleasure to see a green fern in the dead of winter.

Evergreen Christmas fern brightens the winter landscape

Perhaps the best known native evergreen groundcover in our region is Creeping Juniper (Juniperis horizontalis). Juniper is a versatile shrub that provides significant value for wildlife year-round. Its dense branches provide good hiding places, and its berries feed the birds. It prefers dry soil and full sun, but it tolerates some shade as long as the soil is well-drained. It spreads at a moderate rate, and effectively suppresses weeds. Juniper is also tough — it handles being buried by snowplow build-up, even with road salt! It’s a good choice for curb-side plantings and along sidewalks and driveways.

Creeping Juniper is attractive all winter along a property line

You can see another of our favorite evergreen groundcovers in the foundation planting at the Nature Center’s Manor House. Carex laxiculmis ‘Hobb,’ often sold as ‘Bunny Blue’ sedge, is a great groundcover for shade. It’s maybe more “everblue” than evergreen, so its eye-catching color is striking around and under shrubs, and even under shade trees. It will live happily with dense tree roots and spread itself slowly by short runners that sprout new little plants over time. It holds its blue-green strappy leaves all winter long. You don’t have to cut it back in the spring, but if it looks a bit ragged, you can trim the old leaves before new growth begins. Like most grasses and sedges, it is avoided by deer.

‘Bunny Blue’ sedge in winter under shrubs at the Manor House

Plant ‘Bunny Blue’ sedge with other native shade-lovers for a mix of textures. When the other plants go dormant in the fall, ‘Bunny Blue’ will hold the spot until they return

‘Bunny Blue’ sedge in summer in with Maidenhair Fern and Wild Canadian Ginger

For a sunny area, we like Waldsteinia (or Geum) fragaroides, commonly called “Barren Strawberry” because its leaves look similar to strawberry, but it doesn’t bear fruit. Waldsteinia is a deer-resistant evergreen groundcover that likes sunny dry sites and blooms in early spring with bright yellow flowers. It only gets a few inches tall, so it’s great at the front of a flower bed. We planted it last year at the very front of the Nature Center’s new Pollinator Garden. Be sure to come see it bloom this spring!

Spring growth covers bronzed winter foliage of Waldsteinia

Waldsteinia spreads slowly by shallow runners. Use it around a mailbox or lamp post, or along a sunny path. Snow cover and freezing cold do not bother it, and it is hardy to Zone 4. Its leaves may turn bronze by late winter, but new growth will cover the old in spring and form a weed-suppressing mat. And when April showers bring May flowers, you’ll want to be there.

Waldsteinia blooms in late April to early May

This blog is authored weekly by Cathy Ludden, conservationist and native plant educator; and Board Member, Greenburgh Nature Center. Follow Cathy on Instagram for more photos and gardening tips @cathyludden.

January 6, 2022February 14, 2025 Cathy Ludden Around the Grounds, Native Plants

Winter Interest that Pays Dividends

On a cold gray winter day, when the leaves are gone and the last flower is just a memory, finding some bright color in the landscape is a blessing. Discovering “winter interest” in a great native shrub that also provides food and shelter for birds and pollinators is a win-win.

In our last two blog posts, we suggested Winterberry and American Holly with their bright berries to perk up winter views. Here is another of our winter favorites:

Red Osier Dogwood in front of the Manor House

Cornus sericea, commonly called Red Osier Dogwood or Red Twig Dogwood, is a great native shrub that should find a place in the landscape just for its brilliant red bark in winter. But it’s also beautiful the rest of the year – a true four-season plant. In mid-spring, it blooms with flat sprays of fragrant white flowers. All summer, it forms a rounded shape topping out at 6 to 8 feet tall and wide.

Red Osier Dogwood is lovely in spring and summer

In late summer, pretty white berries form to feed the birds. In fall, the leaves turn varying shades of red and purple and begin to drop from the lower branches first, revealing the characteristic red bark. As the shrub matures, you can cut back the older woody stems in spring to encourage new sprouts to come up in vibrant red for the winter show.

Red Osier Dogwood has a wide native range in the United States. It grows on river banks and in wet areas throughout the northern part of the country. It’s a great choice for rain gardens or any sunny area where water collects, especially if you want a low-maintenance natural thicket. Red Osier Dogwood will send out suckers, or shoots, that will root themselves and form new plants to fill in an area. It is an ideal choice for controlling erosion or steep banks in areas that tend to flood. But it will also grow in average garden soil and can easily be controlled by cutting off suckers as they appear.

Red Osier Dogwood with Inkberry and Switch grass on the slope in front of the Manor House

And you couldn’t find a better bird habitat! Red Osier Dogwood provides nesting sites, berries for food, and a supply of caterpillars for baby birds. Like other dogwood species, it is a host plant for the beautiful little Spring Azure butterfly.

So, all these features are dividends for nature while we enjoy the winter interest in our landscape. That’s a pretty good investment!

Red Osier Dogwood and Winterberry brighten a winter day

This blog is authored weekly by Cathy Ludden, local expert and advocate for native plants; and Board Member, Greenburgh Nature Center. Follow Cathy on Instagram for more photos and gardening tips @cathyludden.

December 16, 2021February 14, 2025 Cathy Ludden Around the Grounds, Pollinators

How Can We Help?

News of threats to butterflies, bees, and song-birds is everywhere. We hear that pesticides, climate change, and habitat loss are contributing to shocking declines in bird and insect populations, especially bees needed to fertilize food crops. Scientists report that insects are disappearing. We notice that moths don’t hang around our porch lights anymore, and bugs don’t splatter our car windshields as they once did. We may notice that bird species we often saw as kids are no longer around. We worry about what is happening, but we assume the solutions are beyond our individual control.

“The Insect Apocalypse”
New York Times Magazine, December 2, 2018

The good news is we can make a big difference right in our own back yards! Simple changes in the way we maintain our property – especially in the fall – can have an amazing benefit to birds, butterflies, and bees. We just have to understand what they need and make it available. Birds and insects need food and shelter all year long. Too many of our yards offer neither.

Many of us enjoy seeing winter visitors at our bird-feeders. But birds are vulnerable if they don’t have nearby places to hide. Planting densely with native trees and shrubs, and letting them take their natural shapes, provides shelter and much safer habitat than trimming too tightly to make trees and shrubs artificially neat. Birds need insects they find in holes and crevices in the bark of trees and shrubs, even in winter. So we need to have lots of trees and shrubs all around us, not just up against the house.

Birds need places to hide from weather and predators

Our flower beds and pollinator gardens can be valuable all winter long, too. There are more nutritious seed varieties in native flowers and grasses than in commercial bird seed mixes, so we should leave flower beds uncut until spring.

Most of our native bees over-winter in the ground. Shredded bark mulch prevents burrowing bees from finding the safety they need. Other bee species nest in hollow plant stems. By leaving flower stalks standing through the winter, we can provide habitat for many bee species. At the Nature Center, we have a “bee hotel” to demonstrate that nesting behavior. But it’s easier and far more effective just to leave the stalks of flowers and grasses up all winter long for nest sites.

Artificial native bee winter habitat – note occupied rooms!

Natural winter habitat – uncut flower beds!

Beetles make holes in old tree stumps or fallen logs that are later used by cavity-nesting bees for winter. Brush piles provide winter cover for birds as well as nest sites for bees, butterfly larvae, firefly larvae, and loads of beneficial insects.

Find an out-of-the-way place and stack a winter brush pile

It’s actually easier to create essential habitat for birds and beneficial insects than to strip your yard of all the good stuff in the fall. So, don’t remove your leaves. Don’t over-prune your shrubs. Don’t cut back your flowers and grasses. Don’t bundle up your twigs and branches and put them at the curb. Relax a little instead! There will be time in the spring, after everybody has left their winter beds, to tidy up for the new season. Let’s move toward a more natural look for our winter landscapes and a better environment for the creatures sharing it with us.

We really believe that’s beautiful.

For more information on the value of keeping fall leaves on your property, see our December 2 post here.