Invasives Archives - Page 2 of 2 - Nature Center at Greenburgh

June 9, 2022February 13, 2025 Cathy Ludden Around the Grounds, Invasives, Pollinators

The Trouble With Double

One beautiful spring morning, we stood under our Kwanzan cherry tree and noticed that something was missing: pollinators! Not one bee or butterfly was visiting the tree, even though it was loaded with flowers. Not far away, a blooming crabapple tree was literally humming with pollinators! What accounted for the difference?

We realized that the cherry tree has “double blossoms.” Its flowers have been modified by humans to replace all of its pollen-bearing stamens with flower petals. The flowers are beautiful – but only to people. There is no pollen or nectar for bees or butterflies. The flowers of the crabapple, on the other hand, were loaded with pollen and nectar. And the pollinators were all there for breakfast!

**The stamens are missing completely in these sterile double blossoms**

**The stamens in these flowers are ready for pollinators**

Flowers are the reproductive organs of plants. Pollen contains the genetic material that must be transferred from the (male) stamens to the (female) pistil for pollination (fertilization) to occur. In most flowers, the petals form an outer ring and the stamens are just inside, forming a second ring around the pistil. The flower’s colorful petals, its fragrance, and the sweet juice called nectar all are designed to attract pollinators. As pollinators sip the nectar located at the base of stamens, and collect pollen to feed their offspring, they “accidentally” transfer pollen from flower to flower and deposit it on the pistil where pollination happens. Successful pollination results in seeds, which then grow to produce more plants.

But sometimes nature makes little mistakes. Sometimes a plant will develop extra flower petals where the stamens should be. This is not a good thing for the flower, because with fewer stamens there is less pollen, which reduces the chances of pollination and, therefore, reproduction. In nature, plants that continue to develop too many petals instead of stamens eventually would fail to reproduce.

For hundreds of years, however, horticulturists have been fascinated by this “mistake” of nature. Humans enjoy flowers, and we tend to think bigger and fuller flowers are better. So, when horticulturists discover a flower that has extra petals where stamens should be, they can select that plant for special treatment. They can propagate the plants with extra petals and, eventually, even develop plants with so many extra petals they have no stamens (or pollen) at all! Without stamens, of course, those plants are sterile. They cannot develop fruit or seeds or reproduce themselves.

Roses are a good example. Natural roses have 5 petals surrounding a circle of many stamens carrying pollen.

**A simple rose with 5 petals, stamens with pollen, and pistil in the center**

Roses frequently make the “mistake” of trading stamens for extra petals.

**Note the under-developed petals in the ring of stamens**

Over centuries, horticulturists have selected these “mistakes” for intentional manipulation to create roses that are more interesting to people.

**In fully double roses, extra petals replace virtually all of the flower’s stamens and pollen is scarce or non-existant**

Today we have thousands of flowering trees, shrubs, perennials, and annuals that are popular specifically because they have double blossoms. But this comes with a cost to pollinators. Butterflies need nectar. Bees need nectar and pollen to feed their offspring. Butterfly and bee populations are declining under pressure from loss of habitat, pesticide, and limited food sources. We can help with our garden choices.

**Double peony with no stamens, pollen, or nectar**

**Double trillium with no stamens or available pollen**

**Double sunflower – native, but not useful for pollinators**

**Single peony with stamens and pollinator**

We humans love our double blossoms, but if you’re making a choice, think about providing a big variety of native single-blossom flowers for our pollinator friends!

**A buffet for pollinators in the Nature Center’s meadow**

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.

April 7, 2022February 14, 2025 Cathy Ludden Around the Grounds, Invasives

Let’s “Switch Grass”

Do you have this ornamental grass in your yard? If so, it may be time to switch grass!

Miscanthus sinensis, or Chinese silver grass, is a too-popular ornamental grass so problematic that New York State has regulated it as an invasive species. Switch Grass (Panicum virgatum), on the other hand, is a native ornamental grass that is a perfect substitute. Maybe it’s time to switch?

Ornamental grasses have become increasingly popular as modern tastes have shifted to more naturalistic garden designs. Grasses bring year-round interest, movement, structure, and seasonal changes of palette that enhance every garden. Unfortunately, at least this one non-native grass has created an ecological problem.

**Invasive *Miscanthus sinensis* offered for sale on line**

Sold under the names Chinese silver grass, zebra grass, maiden grass, and porcupine grass, Miscanthus also has many cultivars, including “Morning Light,” “Flamingo,” “Ghana,” “Adagio,” and over 100 others. Despite being identified as invasive by New York and other states, it is still being sold, and is still spreading itself everywhere. It is invading natural areas because it has no biological controls on this continent.

Switch Grass is just as attractive as Miscanthus, just as easy to grow, and just as diverse. An original denizen of America’s prairies and meadows, it has deep roots and is both drought tolerant and deer resistant. It is increasingly available in a huge variety of sizes, shapes, and colors. And Switch Grass is the host plant for very cute native butterflies called, “skippers.”

**Skipper butterflies lay their eggs on Switch Grass**
Photo: Pixabay

**Switch Grass is a beautiful native plant**

Switch Grass is gorgeous through all four seasons, and its versatility is on full display at the Greenburgh Nature Center. The cultivar “Heavy Metal” is steel blue in summer and grows up to 5 feet tall. It is equally impressive in winter when it provides texture, movement, and contrast to evergreen shrubs.

*Panicum virgatum* ‘Heavy Metal’ frames our patio in summer

**The golden tones of ‘Heavy Metal’ contrast with Inkberry and Red Twig Dogwood in winter**

Another Switch Grass cultivar, ‘Shenandoah,’ is 3 to 4 feet tall and has a graceful vase shape that complements both shrubs and perennials. Because it hosts skipper butterflies, it is a great addition to pollinator gardens. Like all Switch Grasses, it enjoys full sun and tolerates poor soil. No supplemental water, no fertilizer, no worries.

***Panicum virgatum*** **‘Shenandoah’ in the Pollinator Garden at the Nature Center**

When we planted the Gerrie Shapiro Memorial Pollinator Garden at the Nature Center last June, we started with tall Switch Grasses as the center “spine” of the garden. Along with ‘Heavy Metal,’ we planted ‘Northwind,’ a Switch Grass cultivar that stays tall, narrow, and straight all season long. These two native grasses support tall flowers that would otherwise flop over when in full bloom. Switch Grass evolved supporting tall wildflower companions in American meadows and prairies, so it’s perfect for that job.

**Tall Switch Grasses define the structure of the new garden**

**A month later, ‘Northwind’ Switch Grass supports tall flowers**

One of our favorite smaller Switch Grasses is ‘Ruby Ribbons.’ At only 3 feet tall, it’s a good choice for smaller gardens. It has multi-colored leaves in shades of red and purple all summer long, and just gets prettier in the fall. Even smaller is ‘Cape Breeze.’ At less than 2 feet, it makes a great edger along the garden path.

And if you want to see what Switch Grass looks like in its natural habitat (almost) come visit our Meadow! After spring mowing, Switch Grasses start showing new growth. By late June, they fill out the Meadow terrain. And in the fall, clouds of tiny seeds hover above the Switch Grass stalks, feeding flocks of birds then and all winter long.

**Switch Grass in the Meadow in the fall**

So, are you ready to switch grass?

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.

December 1, 2021February 14, 2025 Cathy Ludden Around the Grounds, Invasives

Turning Over an Old Leaf

As we learn more about the critical relationships between plants, insects, and birds, the best advice we are getting about fall leaf clean-up is … don’t!

In the old days, suburbanites taking care of their lawns raked (yes, raked!) fall leaves into giant piles to be burned. The familiar scent of burning leaves was everywhere – and we released tons of carbon sequestered in those leaves into the atmosphere.

So anti-burning ordinances were passed, and we started using gas leaf blowers to form the leaf piles, or bagging leaves for municipal workers to collect – all at taxpayer expense. Municipalities started spending millions to ship leaves out of the county. Enterprising souls then turned our leaves into compost to sell back to us. Not a good deal for us.

Bagged leaves to be collected at taxpayer expense

Leaves at the curb clog storm drains, a municipal headache

Since that routine makes neither economic nor ecological sense, we started hearing campaigns urging us to use mulching mowers. The idea was to chop leaves into tiny pieces and leave them on the lawn to enrich the soil. That method is a big improvement, and it definitely works — it’s great for lawn health and municipal budgets.

But we have learned that chopping up leaves has an unanticipated cost. Native bees burrow into the ground under leaf litter to survive the winter. Eggs and larvae of butterflies, moths, fireflies, and many other insects hang on to leaves, or hide under them, until warm weather returns. If we chop up or remove leaves to clear the ground in our yards, we are unintentionally destroying insects that baby birds need for food in the spring, as well as insects we need and enjoy.

Many insects need fall leaf litter to survive winter

Mourning cloak butterfly emerging in March at the Nature Center

The best use of fall leaves – and the best place for them – is under the trees that dropped them. Trees and all other forest plants evolved growing with a thick layer of leaves in the winter. Dead leaves nourish the soil and everything that lives in it. Leaf litter on your shrub and flower beds protects the roots of your plants and protects early buds from freezing and loss of moisture.

Of course, you’ll want to blow (or better, rake!) leaves off of driveways and paths, and either mulch or clear leaves that fall on lawn. But the best place to put them is in your shrub and flower beds and under your trees. A loose, 6-inch deep layer of leaves will not hurt your shrubs and perennials – quite the opposite. If there are still too many leaves, create a leaf pile in an out-of-the-way area, or add leaves to a compost bin. In spring, once the weather is warm and insects have had a chance to emerge, you can mulch the remaining leaves and return them to the lawn or flower beds, or even put them out for removal with spring clean-up.

Use your leaves to protect trees, shrubs, and perennials

Pro tip: Less lawn and more garden makes leaf clean-up a cinch! If your trees are surrounded by garden beds rather than lawn, nature does the work for you!

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.