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Learn more about the plants and gardens at the Chicago Botanic Garden.

What’s black and white and spread all over? Zebra mussels—but they’re no joke.

If you noticed more aquatic “weeds” and algae growing in the Garden Lakes this year—or that our beloved Smith Fountain was MIA after mid-summer—read on to find out why.

Invasive plants and the problems they pose have been the topic of frequent postings here on the Chicago Botanic Garden’s blog. Now we have another invasive species to tell you about—and this time, it’s an animal: zebra mussels.

PHOTO: Adult zebra mussel (Dreissena polymorpha).

Adult zebra mussels (Dreissena polymorpha) are about the size of your thumbnail.

Like many invasive plants and animals, zebra mussels’ native range is a faraway place; in this case, eastern Europe and western Russia. In the past 200 years, they have spread throughout all of Europe and Asia. Here in North America, the first account of an established population was in 1988 in Lake St. Clair (located between Lakes Huron and Erie), likely arriving here as tiny hitchhikers in the ballast water of a single commercial cargo ship traveling from the north shore of the Black Sea.

Somewhat remarkably, over the next two years they had spread throughout the entire Great Lakes. Just a year later in 1991, zebra mussels had escaped the Great Lakes and begun their march across North America’s inland waters. (Watch an animation of their spread). Today they are found in at least 29 states.

A zebra mussel may live up to five years and produce up to one million eggs each year—that’s five million eggs over their lifetime. A freshwater species of mollusk, they prefer to live in lakes and rivers with relatively warm, calcium-rich water (to help support their shell development). They feed by filtering microscopic algae from the surrounding water, with each adult zebra mussel filtering up to one liter of water per day.

Though tiny in size (adults are typically ½ to 2 inches long), their ecological and economic impacts can be enormous. Adult zebra mussels prefer to attach to hard surfaces such as submerged rocks, boat hulls, and pier posts—but they also cling to water intake structures as well as the interior of most any pipe that has flowing water in it (such as drinking water supply and irrigation system piping). From an ecological perspective, zebra mussels’ removal of microscopic algae often causes the afflicted waterway to become much more “clear.” While this clearer water may otherwise seem like a good thing, the now-removed microscopic algae is an important food source for many native aquatic animals. The clearer water also allows sunlight to penetrate deeper into the water, thereby stimulating much more rooted aquatic plant growth.

Nearby, zebra mussels were first identified in 2000 at the Skokie Lagoons, just south of the Garden. In 2013 and again in 2014, just a few zebra mussel shells were found at the Garden on the intake screens for our irrigation system’s South Pumphouse. Since so few mussels were found, we were hoping that the Garden’s lakes were simply not a hospitable place for the zebra mussels to flourish. Unfortunately, that thinking all changed in 2015….

PHOTO: Waterfall Garden label covered in zebra mussels.

These zebra mussels, only a few months old at the time, completely covered this plant label that had inadvertently fallen to the bottom of the Waterfall Garden’s upper pool.

At our Waterfall Garden, 1,000 gallons per minute of lake water are pumped to the top of the garden, after which the water flows down through the garden’s channels and then back into the lake. When Garden staff drained the Waterfall Garden for cleaning in June 2015, there were no apparent zebra mussels present—but by September 2015, the entire bottom of the Waterfall Garden’s upper pool was completely encrusted with attached zebra mussels. Needless to say, we were more than a little alarmed.

Realizing that the Garden’s lakes could indeed support massive growth of zebra mussels, the Garden’s science, horticulture, and maintenance staff quickly came together to devise a remediation strategy that would protect two critical components of the Garden’s infrastructure from “clogging” by zebra mussels: our irrigation system (which utilizes lake water to irrigate nearly all of our outdoor plant collections) and our building cooling systems (three of our public buildings extract lake water to support their air conditioning systems).

PHOTO: One of the Garden's lake water filtration systems.

Automatic backwash filters like the ones pictured here will be added to each of the Garden’s three pumping stations that withdraw lake water to irrigate nearly all of our outdoor plant collections.

The Garden’s zebra mussel remediation team drew upon the best scientific expertise available in North America, which confirmed that there is no scientifically proven approach for removing all zebra mussels from a body of water. The team explored all potential options for eliminating zebra mussel impacts on our infrastructure, and ultimately settled on two approaches: first, the installation of automatic backwash filters to keep even the tiniest of zebra mussels from getting into our irrigation system (the youngest zebra mussels are about 70 microns in size, or about the width of a human hair), and second, the installation of conventional closed-loop “cooling towers” on the three Garden buildings that currently use lake water for air conditioning (thereby discontinuing all withdrawals of the lake water for building cooling). Final design of the backwash filtration systems and the cooling towers is currently underway, and our intent is to have everything installed and operational by spring 2017.

PHOTO: The Garden’s aquatic plant harvester cuts and removes excessive aquatic vegetation and algae from the Garden lakes.

The Garden’s aquatic plant harvester cuts and removes excessive aquatic vegetation and algae from the Garden lakes.

If you visited the Garden in 2016, you probably witnessed some of the zebra mussels’ ecological impacts to our lakes. Mid-summer lake water transparency in our lakes typically is about 3 to 4 feet—but in 2016, this increased dramatically to about 6 feet (likely due to the zebra mussels’ filtering abilities described earlier). This clearer water resulted in much great submerged aquatic plant growth in our lakes, and our aquatic plant harvester struggled to keep up. Many visitors commented that there was much more aquatic “weed” growth in the lakes this year—and they were correct.

In fact, there was so much aquatic plant growth in our lakes this summer that the water intake for Smith Fountain in the North Lake became clogged and the pump burned out. Look for a repaired Smith Fountain (with a more clog-resistant intake) to reappear next spring.

PHOTO: The Smith Fountain (which is illuminated at night) is an acclaimed feature in the North Lake.

The Smith Fountain (which is illuminated at night) is an acclaimed feature in the North Lake.

While there currently is no known way to eliminate zebra mussels from freshwater lakes and streams, Garden researchers intend to utilize the new aquatic research facilities in the emerging Kris Jarantoski Campus to explore experimental approaches, such as biological control agents, to potentially lessen the zebra mussels’ ecological impacts to our 60-acre system of lakes. Stay tuned.

©2016 Chicago Botanic Garden and

Leaves are green. There are very few exceptions in healthy living plants, and most of the exceptions are partially green with red, yellow, orange, or white patterns; or they look white, but upon closer inspection they are actually whitish, bluish-green, and not pure white. The pigments that give all leaves their color are essential for the plant’s ability to harness energy from the sun and make sugars in the process we know as photosynthesis.

But every once in a while, a completely white seedling sprouts from a seed. This happened with some basil I grew a few years ago. 


PHOTO: this picture shows two seedlings, one has two green seed leaves and the other is white and only half as big.

The green and albino seedlings came up at the same time, but the albino seedling never grew true leaves, and eventually withered and died.

My albino basil survived only a few days. Without any chlorophyll—the green pigment necessary for photosynthesis—this seedling was doomed. That is the case with all albino plants. The gene mutation that gives rise to albino plants is fatal to the plant, because without the ability to make sugars, the plant runs out of energy to live.

So when I was perusing the online Burpee seed catalog and came across “variegated cat grass” I was curious. VERY curious, and perhaps you are, too.

PHOTO: a potted plant of white grass leaves.

How can this albino plant survive? (Photo permission from W. Atlee Burpee Company)

I had several questions: 

  • The term “variegated” implies that the leaves would be striped or multicolored, but in the picture it appears that there are all white leaves. What will this grass actually look like?
  • How long will it take to sprout?
  • How easy it to grow?
  • Is there enough green on those leaves for the grass to survive or will it die off like my basil?
  • If it does survive, how long can I keep it growing?

And most importantly:

  • Would this make an awesome science activity for students in the classroom and at home to investigate the importance of chlorophyll in plants?

There was only one way to find the answers. I ordered the seeds and grew some variegated cat grass in our nature lab at the new Learning Center. You can do this in your classroom to find answers to my questions and your own. 

Before I give you directions for growing cat grass, you may be wondering:

What IS cat grass?

The cat grass you may have seen sold in pet stores is usually a type of wheat, or Triticum. Our “variegated cat grass” is a type of barley (Hordeum vulgare variegata). Both are cereal grains that have been cultivated as food for hundreds of years. Both are sold commercially as cat grass because some cats like to chew on the leaves. Not being a cat owner, I don’t know if cats actually like this stuff, but apparently it sells.

Variegated barley was the result of science experiments on genetic mutations in barley seeds in the 1920s. The hybrid barley seeds have been packaged and sold by different seed companies because…well, they’re attractive and intriguing—they caught my attention.

How to plant cat grass, barley, wheat, or any grass seeds

You need:

  • A container that will hold soil at a depth of at least 2 inches; drainage holes are best, but not necessary
  • Variegated cat grass seeds (sold as “cat grass, variegated” and available at Burpee and other seed suppliers)
  • Potting soil
  • Water
  • A warm, sunny location for your plants


PHOTO: Twelve plants have sprouted, one green, three green and white striped, and the rest all white.

In less than a week, a few more than half of the twenty variegated cat grass seeds planted in this 4-inch pot grew to 4 – 6 inches tall. The taller plants are ready for a trim.

Fill the container with moist potting soil. Spread seeds on the surface of the soil. Cover seeds with a thin layer of moist soil and tamp the soil down so that most of the seeds are covered. It’s all right if you can see some of the seeds through the thin layer of soil. Place in a warm, bright location. The seeds will sprout in a few days, but may take a week depending on the room temperature.

If students plant their own individual pots, have them place 20 – 30 seeds in each 3-inch container. The seeds I bought came 300 to a pack, so that means you need at least two (maybe three) packs to have enough for everyone in the class.

PHOTO: most of the grass is all white, but there are nine or ten all or partially green leaves.

Half of the 100 seeds planted in this 8-inch pot have sprouted, and more should be coming up soon.

You can also use the whole pack in a 8- to 10-inch container, or even spread more seeds in a foil baking pan filled with soil to grow a carpet of grass. The more densely you plant the seeds, the closer the plants will grow together and it will look and feel more like a healthy lawn. A sparser planting makes it easier to observe individual plants. It’s up to you how you want to do it, really.

Keep the grass in a warm, sunny location. Water when dry, but do not allow it to dry out. When the grass leaves are more than 3 inches tall, use a sharp pair of scissors to trim them to a uniform height just as you would mow a lawn. This will prevent the grass from going to seed and keep it alive longer. You can plant new seeds in the same planter to revitalize in two to three weeks when it starts looking a little tired.

Now the REAL science part: 

Whether you make a single classroom planter or have each student plant her own pot, observe your variegated cat grass for the next four to six weeks, or even longer. Keep it watered and trimmed. Measure its growth. Take photos or sketch it to record how it grows and changes. Ask your own questions and try to find answers, and ultimately reach a conclusion about what happens to white plants. If you and your class are really interested, plant some more cat grass and change the procedure to test your own ideas. It’s that easy to do plant science in your classroom.

Want more albino plant science? Read on.

More activities for inquiring minds

You can experiment with other genetically modified albino seeds available through science supply companies.

PHOTO: A packet of genetically modified corn seeds and instruction booklet

Seed kits enable you to investigate different genetic traits, including the albino mutation.

Carolina Biological Supply Company sells hybrid corn that will grow white leaves and stems. I have planted these seeds and they work pretty well, but require a bright window or light and a warm environment to sprout successfully. A classroom kit contains soil, planting trays, and 500 seeds for a classroom investigation, and costs about $100. You can order just the seeds in packs of 100 genetic corn seeds that are all albino (90 percent of the seedlings will grow to be albino) for $18.50, or a green/albino mix—which means about 75 percent of seedlings will be green and 25 percent white, for $10.50. The latter enables you to compare the mutation to the normal strain. 

PHOTO: Ten white corn seedlings are a few inches tall.

Five days after planting, albino corn seedlings are beautiful, but ill-fated.

Nasco sells seeds and kits to investigate albino plants. Their “Observing the Growth of Mutant Corn Seeds” kit serves up to 40 students and costs $62.50. Nasco also has albino tobacco seeds with 3:1 green to white ratio, 1,200 seeds for $12.05. Tobacco seeds are smaller, and therefore more difficult for little fingers to handle than corn or barley. I have never tried growing them, but that might be my next science project this fall.

PHOTO: eight inch glass planter with green grass and label that says: Cat Grass (Barley).

After a two months, my densely planted variegated cat grass is thriving at the nature lab, even though it no longer resembles the catalog photo.

The answer to my question? Yes! This is an awesome science activity for students because it’s easy and demonstrates something really important—in fact, something essential to our existence!

You don’t need to purchase the fancy kits to investigate why plants are green. You can get a lot of good science learning out of a pack of variegated cat grass. All you really need to do is look around you and notice the colors in nature. Do you see white leaves anywhere? If you do, then there is probably a science investigation waiting for you.

©2016 Chicago Botanic Garden and

Under a grey fall sky, the English Walled Garden was blooming with color, activity, and life. Rain-glazed flowers drew tiny hummingbirds, and fountains sang. It was a special day. John Brookes, the English landscape architect who designed the suite of gardens was there for a visit, something that has happened only once every few years since the beloved site was dedicated in the summer of 1991.

PHOTO: Clematis bloom through a wall in May in the English Walled Garden.

Clematis blooms through a wall in May in the English Walled Garden.

Although the garden has grown and changed since that time, it has remained true to the original concept Brookes created. “There’s an intimacy about it that I think people like,” said Brookes, who strolled the space with a small team of Garden staff members. “I don’t think there’s another area that has this range of plant material in it,” he added.

Before entering the garden, Brookes paused to soak in the entrance plantings along the west wall, evaluating the shape, color, and size of each shrub, flower, and vine. The vibrant section had been replanted since his last visit, but he nodded as if in agreement as he swept his eyes over the arrangement.

He was next drawn to the perimeter of the garden that overlooks the Great Basin. The border of the space and the height and shape of trees and shrubs were his first priorities there and throughout his tour. Neatness was fundamental in his view, as he looked for carefully arranged edging such as boxwood bushes. However, in places such as the daisy garden, he encouraged the horticulturists to allow for wild messiness, and for tall, abundant blooms that create a relaxed feeling.

As he walked from one garden room to the next, he admired splashes of color and white flowers that brought a light touch to the many deep green plantings and shady areas. He looked over the shoulders of a cluster of art students who were painting their own vision of the space, and nodded with approval.

PHOTO: Sunlight shining through apples in spring bloom create dappled shade over foxglove in the English Walled Garden.

Sunlight shining through apples in spring bloom creates dappled shade over foxglove in the English Walled Garden.

PHOTO: The yellow blooms of Magnolia 'Elizabeth' are a beacon of spring in the English Walled Garden each year.

The yellow blooms of Magnolia ‘Elizabeth’ are a beacon of spring in the English Walled Garden each year.

PHOTO: Blooming through late fall, the morning glory vines captivate visitors to the English Walled Garden.

Blooming through late fall, the morning glory vines captivate visitors to the English Walled Garden.

PHOTO: Preparing to bloom, morning glory vine creeps up the wisteria arbors of the English Walled Garden in midsummer.

Preparing to bloom, morning glory vine creeps up the wisteria arbors of the English Walled Garden in midsummer.

Again and again, he paused, considered, discussed, and nodded, occasionally spotting a new addition to the garden, or the absence of a plant that had once lived there. Always, he was looking for brightness in the form of blue, yellow, and white flowers, silvery accents, and varied vines against red brick walls. Sitting beside a trickling fountain, he noted the importance of the many water features. “It brings it alive,” he said. Water “brings light down into the garden because you get a reflection. It’s the sound, really,” he added.

PHOTO: John Brookes, the landscape architect who designed the suite of gardens known as the English Walled Garden.

John Brookes, the landscape architect who designed the suite of gardens known as the English Walled Garden.

Returning to the perimeter of the garden, he stopped to take in the view from beneath an English oak that was planted by Her Royal Highness Princess Margaret in 1986, when ground was broken for the garden.

Brookes’ design was inspired by several gardens in England, including the gardens of Russell Page and the Great Dixter gardens.

Returning to the tour, Brookes and the team of Garden staff anticipated the arrival of mums and asters in the coming days. Like a proud parent, Brookes said that the garden has “just grown and matured,” since it was first planted. “It feels like a real garden more than a show garden.”

A brightly colored butterfly swept by as if to say “thank you,” while a photographer snapped a photo of a hummingbird and several women in wide-brimmed hats gathered on benches to chat. A vision come to life.

©2016 Chicago Botanic Garden and

As fall approaches and the leaves begin to change, the Chicago Botanic Garden bids adieu to our beautiful summer blooms until next year. The air starts to get crisper (and your summer plants will too), but September isn’t the expiration date for color and excitement at the Chicago Botanic Garden—and it shouldn’t be in your garden either.

We asked Tim Pollak, outdoor floriculturist, and Cindy Baker, manager of horticultural services, for their favorite fall-blooming perennials that will make your landscape pop this season.

PHOTO: Phlox paniculata 'Barfourteen' Purple Flame® garden phlox.

Purple Flame® garden phlox (Phlox paniculata ‘Barfourteen’)


Phlox paniculata
Garden phlox

Look no further for a long-blooming and beautiful native perennial that provides a whole palette of color options for your garden. Phlox cultivars add shades of showy pink, lavender, or white in clusters of delicate-looking flowers. Their sweet fragrance will attract late-season butterflies and hummingbirds to your own backyard. Garden phlox are generally hardy plants and will grow well in sun or shade. Plant in midspring with a layer of mulch to retain soil moisture for maximum flower production.

PHOTO: Panicum virgatum 'Dallas Blues' switchgrass.

Switchgrass (Panicum virgatum ‘Dallas Blues’)

Panicum sp.

Ornamental grasses may not seem like an obvious choice for garden excitement but they can help to create texture and movement. Switchgrasses are an environmentally smart choice as they are native to tallgrass prairies in the United States. Cultivars are variable in color with red to light golden blooms and deep green to blue blades. Switchgrasses are low maintenance and will tolerate nutrient-poor soils, but plant in full sun to keep plants upright and blooming all fall. Because they can grow up to 8 feet in height, consider planting toward the back of your beds and place smaller plants in front.

PHOTO: Callicarpa japonica 'Leucocarpa' (Japanese beautyberry).

Japanese beautyberry (Callicarpa japonica ‘Leucocarpa’)

Callicarpa sp.

This small shrub has something to offer year-round; it blooms in the summer, then its flowers are replaced by small berries that last until winter. Depending on the species, Callicarpa can have shiny white or bright purple berries—both are a big hit with birds. All species have long, arching branches that cascade outward but with pruning, the shape is variable. Beautyberry should be planted in rich soil and pruned in early spring but otherwise requires little attention throughout the year. Ensure your shrub receives adequate moisture for maximum fruit production all fall long.

PHOTO: Rudbeckia hirta 'Autumn Colors'.

Black-eyed Susan (Rudbeckia hirta ‘Autumn Colors’)

Rudbeckia cultivars
Black-eyed Susans and coneflowers

With familiar daisy-like flowers that will bloom through all of fall, it is no wonder that species of Rudbeckia are a fall favorite. Petal colors can range from shades of bright yellow to orange-gold, and some cultivars have flushes of red on the petals. Rudbeckia will respond well to deadheading or alternatively, leave the dried flower heads on the plant to attract migrating birds to your garden. This will also allow the flowers to reseed because not all cultivars of Rudbeckia will act as perennials in colder climates.  These flowers are low maintenance if planted in well-drained soil.

PHOTO: Imperata cylindrica 'Rubra', or Japanese blood grass.

Japanese blood grass (Imperata cylindrica ‘Rubra’)
Photo by Jim Hood, via Wikimedia Commons

Imperata cylindrica ‘Rubra’
Japanese blood grass

Japanese blood grass is another low maintenance ornamental grass. Usually smaller in stature than switchgrass, it introduces a dramatic splash of deep red into your landscape. Although nonnative and normally a fiercely invasive plant, this cultivar does not produce seed and spreads slowly. This grass is best used as a border plant in well-drained soils.

©2016 Chicago Botanic Garden and

In the past year, more than 181 million people learned about Spike, Alice the Amorphophallus, and Sprout—the Chicago Botanic Garden’s titan arums (Amorphophallus titanum) that entered a bloom cycle—through various media sources.

Now even more people may have the chance to learn about the unique corpse flower from seedlings sowed at the Garden that have been shared throughout the United States.

It all began about 12 years ago when the Garden procured titan arum bulbs and seeds, which we carefully cultivated until they were ready to flower. With the bloom cycles of Alice and Sprout, we wanted to try to pollinate our plants. In nature, titan arums are pollinated by carrion beetles. Since such insects don’t exist at the Garden, we needed to do the work ourselves. As Spike, Alice, and Sprout are thought to be very closely related (with very similar genetic makeup), we speculated that fertilization with pollen from our first titan—Spike—to Alice would not occur: they were “self incompatible”—a term that often describes a plant species that is unable to be fertilized by its own pollen. So in addition to Spike’s pollen, we looked for genetically different pollen. Fortunately, the Denver Botanic Gardens also had a titan arum (“Stinky”) in bloom last year, and they sent us some of Stinky’s pollen, which we used to pollinate Alice.

After the pollination, Alice developed large, plump red fruits. These fruits were harvested and cleaned, and Deb Moore, part of the Garden’s plant production team, sowed the seeds. The result: about 40 quick-growing seedlings—each a single titan arum leaf

We decided to keep a few seedlings for our own uses, but we really wanted to share these young plants with the broader botanical community. We contacted institutions in the American Public Gardens Association to see if any would be interested in acquiring an Amorphophallus titanum.

We had great response. Seedlings were sent to 27 institutions (see Google map above), including the Cincinnati Zoo and Botanical Garden; the JC Raulston Arboretum at North Carolina State University; the Botanic Garden of Smith College in Northampton, Massachusetts; Ganna Walska Lotusland in Santa Barbara, California; the University of Idaho Arboretum and Botanical Garden in Moscow, Idaho; Smithsonian Gardens in Washington, D.C.; University of California-Davis Department of Plant Biology; and of course, three seedlings went to the Denver Botanic Gardens to grow alongside Stinky. 

©2016 Chicago Botanic Garden and