Thursday, February 27, 2020

Project Swallowtail Plant List - Key plants for Swallowtail Butterflies

This is the first of several pages that will list native plants we are using to support native pollinators in Project Swallowtail. This page highlights species we're using to support native Swallowtail butterflies. Other pages will give more complete list of trees, shrubs, perennials, and grasses beneficial to different birds, bees, butterflies and other pollinators.

But first, let me direct you to a previous post on just this subject: Hops and Spice, Pipes and Paws - How Large a Tale will you Swallow? That post has fun with some of the history around these plants, animals, and human customs.

Our plant list for swallowtails:

  • Hoptree
  • Pipevine
  • Pawpaw
  • Spicebush
  • Sweet crabapple
  • Tuliptree
  • Black cherry
  • Pussy willow
  • Aniseroot
  • Golden Alexanders
  • Great Angelica
  • Anise, caraway, coriander, dill, fennel, lovage, and parsley

Details - see below!


Giant Swallowtail
Giant Swallowtail, Gordon Roberton CCbySA3.0

There are only two Ontario native plants Giant Swallowtail caterpillars will eat, and one of them, Prickly Ash, is a monster in the garden. Don't go there, unless you have a big property, and you want to be able to say, as Sean James does, "kiss my Prickly Ash" to annoying visitors.

Instead, we're planting Hoptree (Ptelea trifoliata). This shrub to short tree (up to 6m tall but can be pruned much shorter; 2-3 m along the shores of Lake Erie) thrives in the sandy soils found in our area, and is not too particular about light or moisture. 

Ptelea trifoliata 'Aurea' ; photo Karl Gercen
We'll be using plants grown from local seed, but if you are into foliage colors you can consider the variety "Aurea" which won a RHS Award of Garden Merit for its pale spring leaves.

I wrote about hoptrees and giants in this post which you can peek at for more details, including how to grow your own from seed.

Be sure to look online for images of Giant Swallowtail caterpillars so you can recognize them when a female has found your bush! 


Pipevine swallowtail, ©Troy Bartlett

Pipevine Swallowtail

Here's another butterfly with only a single native host, the pipevine Aristolochia macrophylla. This Appalachian species is at the northern limit of its natural range with us, although it was in much demand a century ago as a way of shading porches. The pipevines are a large family in the tropics, and they all share compounds in their leaves which are very bitter if eaten. Like the monarch does with milkweed, Pipevine swallowtail caterpillars store up these bitter compounds so that the adults are very nasty tasting for birds.

Pipevine can be a vigorous grower where it is happy. A fence is an ideal spot for it, like the big spread of it on Ward's Island near the Island Cafe, which used to harbour many of these butterflies. Most soils are OK, but the vine doesn't like to be too dry. I've seen it growing well in half shade.


Zebra Swallowtail

The only local host for the elegant Zebra swallowtail is the pawpaw tree, whose very tasty fruit is a fine
reward for pollinator gardeners in the fall.

It takes two different pawpaws to cross-pollinate and set fruit, and being a small tree they may take five years after planting to reach blooming size. But after just a few years zebra swallowtails can lay eggs on the leaves - they don't care about the fruit.

In nature, pawpaws are often found in moist soil near streams or rivers, and can tolerate partial shade. Once they reach blooming size, they send up new stalks from suckers. I trim mine off once a year, a 10 minute task.

My two pawpaws were grown from pawpaw fruit from the Niagara area, sold by a farmer in the Dufferin Grove Organic Market. I know of at least two other properties in our area with large, well-yielding pawpaws.

Spicebush Swallowtail

Spicebush swallowtail
Compare the blue hind wings of the Spicebush and Pipevine swallowtails. They are part of what biologists call a mimicry complex. Lindera benzoin - Spicebush - is the favored host plant for Spicebush caterpillars, and also for the Promethea moth. The Tiger Swallowtail and the Imperial moth also feed on the leaves.

Spicebush has small but fragrant yellowish flowers in spring and red fruit in fall, although there are separate male and female plants, so you need one of each within a few back yards of each other to get fruit. Fruit, leaves, and stems are aromatic and have been used in teas and other recipes.

Spicebush blooms more in the sun but tolerates shade very well. My bush is planted north of an old pear tree where it gets several hours of afternoon sun.

These swallowtail caterpillars can also feed on Tuliptree leaves - see the Tiger Swallowtail, below.

Male spicebush flowers - public domain
Imperial Moth, Joel Mills, CCbySA 3.0

Tiger Swallowtail
Eastern Tiger Swallowtail, Derek Ramsey CC by SA 3.0

As a child I didn't know that "Tigers" could be one of several very closely related species. The USA tiger's caterpillars feed on Tulip Trees and a fair number of other trees, the Canadian tiger replaces tuliptrees with poplars, and there is a hybrid species left over from the ice ages in the Appalachian mountains. 

To add more to the confusion, the females can either be traditionally tiger-colored or have a black form which looks a great deal like the Black Swallowtail (below).

There are about 7 or 8 host plants for the Tigers, but the ones we are featuring in Project Swallowtail have benefits for other pollinators too. These are the Tulip Tree, Black Cherry, Sweet crabapple, Pussy Willow, and our friend the Hoptree (above).

crabapple, Per Palmkvist Knudsen,
CCbySA2.5

Sweet crabapple

Malus coronaria is native to our region and an excellent small garden tree, for pollinators in spring, caterpillars in summer, and birds in fall. Full sun produces the greatest bloom and fruit set. Jam is delicious!





Tulip tree, Clement Kent CC by SA 3.0

Tulip Tree

Liriodendron tulipifera is a native giant magnolia - up to 50m/160ft in the south. An excellent shade tree, we planted it in Kathy's Garden to give shade and beauty to seven future generations, as the ash and beech and Austrian pine trees around it die over the next few years. It's valued for its wood.

Honeybees love tuliptrees in bloom, and make a flavour-rich dark honey from it. A friend gave me a jar of it from a grove in Ohio, which I save for special occasions.

Tuliptree Silkmoth, Thomas Barnes Public Domain
Tuliptrees are native to Carolinian Canada, but used to be rare in Toronto. A friend now grows them as far north as Creemore. The City of Toronto has added them to the list of trees the city will plant for free in your front yard if you ask. Several in the Dufferin Grove neighbourhood have now reached 3 stories tall - this tree can grow several feet per year when young!

 It hosts "only" 28 species of native moths, including the giant Tuliptree Silkmoth, and of course the tiger swallowtail.

Black Cherry

Prunus serotina is like sweet crabapple - flowers in spring, leaves in summer, and fruit in fall for birds. It's like tuliptree as it is a large tree with valuable lumber which can live hundreds of years. 

I had a property on the shore of Lake Huron with one enormous Black Cherry and several of its children. The big tree had been struck lightning but survived. Just down the hill to the lake grew Alternate-leaved Dogwood, whose blue or purple berries ripened just after the cherries. We had torrents of birds for those weeks!







Emperor moth. Jena-Phillippe Harmon, CCbySA 3.0
Talk about beauty: Coral Hairstreak, Eastern Tiger Swallowtail, Red-Spotted Purple, Spring Azure and Viceroy butterfly and Io, Cecropia, Promethea, and Emperor moth caterpillars feed on the leaves - it's one of the top trees in ecologist Douglas Tallamy's list of best trees for wildlife.











Pussy Willow

Pussy willow - Silk666, CCbySA 3.0
The native willow Salix discolor is a champion at supporting pollinators, and children! A few stems of "pussies" is one of the finest signs of spring. Keep them in water for a few weeks and you'll find roots on the lower stems. Plant them out in a sunny, moist spot and in just a few years you'll have pussies of your own to give away.

I watch my cut stems carefully. Pussy willows have male and female plants. If the soft white of the buds is replaced by golden pollen-bearing stamens, you have a branch from a male tree. The early spring pollen is incredibly valuable to early spring bees, including honeybees and bumblebees.

And the butterflies and moths! Another Tallamy favorite, pussy willow supports Acadian hairstreak, black-waved flannel moth, cecropia moth, Compton's tortoiseshell, cynthia moth, dreamy duskywing, eastern tiger swallowtail, elm sphinx, imperial moth, Io moth, modest sphinx, mourning cloak, polyphemus moth, promethea moth, red-spotted purple, small-eyed sphinx, twin-spotted sphinx, and viceroy. In fact, a small grove of willows is one of the best ways to guarantee seeing mourning cloak butterflies on mild days in late fall and early spring. 

OK, enough about Tigers and their hosts. One more swallowtail to go:


female black swallowtail, Kenneth Dwain Harrison CC by SA 3.0

Black Swallowtail

The black swallowtail Papilio polyxenes is probably our most common swallowtail. Males and females are both black but differ in the amount of blue (mimicking the pipevine swallowtail).




male black swallowtail, D. Gordon Robertson CC by SA 3.0
Males defend mating territories fiercely, and if you visit a hilltop in High Park in summer you may see an aerial battle between two males. 

Females search for plants from the carrot/Queen Anne's lace family to lay their eggs. Given the abundance of the invasive but well established Queen Anne's Lace (wild carrot), they don't have to look far.

If you want some native plants to feed black swallowtail caterpillars and provide blooms for other pollinators, I recommend three. 

The dappled-shade adapted Aniseroot sweet cicely (Osmorhiza longistylis) has anise-scented and flavoured leaves and springtime white flowers. 

Golden Alexanders
Derek Ramsey CCbySA 3.0

Golden Alexanders (Zizia aurea) has beautiful yellow clusters in May or June; it dies back if the soil gets dry. In addition to the black swallowtails, the solitary mining bee Andrena ziziae feeds its young only the pollen of Golden Alexanders. I have it in a spot with half a day's sun.




Great Angelica (Angelica atropurpurea) is a native perennial we should know better. Its sweet stems and roots were used for making candy, and Indigenous peoples have a number of medicinal uses for it. With golden blooms on purple stems three to six feet tall, it is a major plant in the water or rain garden. It needs moist soil and a reasonable amount of sun. Hordes of smaller pollinators will be attracted to the blooms.

Black Swallowtail caterpillar
@401rooftopgarden  - CC by SA 3.0
And then, there are all the non-native but delicious herbs that will feed black swallowtail caterpillars. Anise, caraway, coriander, dill, fennel, lovage, and parsley are some of the more common ones. On the rooftop garden of 401 Richmond in downtown Toronto, gardener Saskia Vegter found caterpillars last year, showing that apartment dwellers can attract this butterfly.














Thursday, February 6, 2020

Balcony Herbs for You and for the Pollinators

Many of us live in apartments, without a plot of earth for a garden. If you want to treat yourself and pollinators well, what should you grow in pots or planters?

My answer is Herbs. They'll be great for you in the pot, pan, or salad, and if you manage them right, full of flowers for pollinators. Further, many herbs are very tolerant of the wind and drying conditions of an upper-floor balcony, so they'll be easier for you to grow than other flowering plants.

Basil flowers - by Natalie Ward
Basil is one of my favorites. Even though I have a back yard, it's too shady these days for basil to get the full heat and sun it needs. So, I grow it in pots on the deck.

Carpenter Bee on Basil - Gideon Pisanty,
 CC by SA 3.0
Many people trim off the basil flower spikes, because it prolongs the growth of the leaves. But the flowers are excellent in salad, and very
attractive to pollinators.

If you have a big pot, I'd recommend a mix of sweet basil, lemon basil, Thai basil, and holy basil. Put it next to your patio tomatoes to remind you to use the leaves with tomato dishes!

Thyme in a pot - Greenmars, CCbySA 3.0

I never have enough Thyme!  It's highly tolerant of drying and heat. Many varieties are winter hardy. You can find half a dozen different flavors and forms, with flowers ranging from pink to pale purple to white. As with basil, if you have a long window box, try mixing several varieties together. The flowers are edible but strong tasting, so best in soups and stews.

I hope I don't need to remind you not to use pesticides on your herbs???


Coriander/Cilantro - H. Zell, CC by SA 3.0
 A fantastic group of herbs to grow from seed in pots are the carrot family herbs dill, fennel, and coriander (Coriandrum sativum). They grow easily from early spring sown seed, but they need a but more watering than thyme does. Flowers, of course, are their way of making the yummy seeds, so do double duty on your balcony. However, these annual plants die back after the seeds ripen, so plant several waves of them spaced about two weeks apart for whole season enjoyment.

Dill in full bloom - Clement Kent, CC by SA 3.0
If you use the leaves (coriander leaves = cilantro), you can pinch one of these plants several times to get it to grow more bushy. Then when you stop pinching, you'll get an explosion of flowers.




 In summer heat, the leaves can be all too fleeting. Of course, you can dry them, but my in-laws used to freeze dill  (Anethum graveolens) just after picking, to have fresh green sprigs on potatoes or fish - an Estonian favorite!


Fennel -  K√∂hler's Medicinal Plants (1887)





"Above the lower plants it towers,
The Fennel with its yellow flowers;
And in an earlier age than ours
Was gifted with the wondrous powers
Lost vision to restore." - Longfellow, The Goblet of Life, 1842

Fennel (Foeniculum vulgare) is biennial, so it doesn't bloom until the second year. In the ground it is quite hardy but in you may need to wrap the pots to bring it through our winters. Remember, Longfellow warned you it will grow tall! Bronze Fennel is an attractive variety.




A bed of Chives in June - Clement Kent, CC by SA 3.0

Bumblebees like Chives

Garlic Chives - Clement Kent, CC by SA 3.0
Chives (Allium schoenoprasum) make a good pot plant, although I find if not watered enough they get rather bitter. For the purple species, blooming is in early summer. Remove the flowers when they fade for a smaller bloom later in the summer.









Chive flowers are longish, favoring bumblebees.

At my friend Jon's cabin near northern Georgian Bay, chives have naturalized on the granite rocks where they grow in a very, very thin layer of gravel. They also grew on nearly bare granite at my parents' cabin near Thunder Bay. So I can say with complete confidence that they will be hardy in your pot on the balcony.


"He who bears chives on his breathe,
Is safe from being kissed to death."
Marcus Valerius Martialis, 80 A.D.

Martial's epigram is even more true for Garlic Chives (Allium tuberosum), whose leaves have the added flavor and scent of garlic. I used to grow these under the kitchen window for a milder addition to salads than a crushed garlic cloves, but they seeded so abundantly I had to exile them to the back of the yard. Flowers arrive in late summer, and are attractive to pollinators, but too strong-tasting to me to use in the kitchen.



Spanish Tarragon - George Hull, CC by SA 2.5
Did you know that there are many species of marigolds in Mexico? Tagetes lucida is also known as
Spanish Tarragon. It's completely unrelated to French Tarragon, which tends not to thrive on balconies. But the Spanish Tarragon marigold is happy in sun and baking heat. The leaves are good in many of the same recipes where you'd use a regular tarragon. And, in late summer/early fall, you get many small yellow flowers for the bees.




Wow - so many more herbs to go! For sunny planters I'd also recommend marjoram and oregano, both great bloomers and worthy in the pot or on the pizza. But let's turn to those of us whose site faces north, or an adjoining building.



Make mine Mint! There are many species of mint (Mentha) and most of them will tolerate some shade. They are better in pots than in the soil, because they tend to runner about and take over the garden if you let them. They are of course an essential of herbal and Mediterranean teas, and of many kinds of cooking recipes. There is spearmint, peppermint, lemon mint, chocolate mint...the list goes on.

I've put multiple mints in one pot, and this works fine for the first year. But by the second and later years one has driven the others extinct.

Flowering happens frequently, and I like to add the flower spikes to fresh mint-water for summer hot days. But, please pick them off when they are done, or your plants will tend to get woody and leggy.

There are many other herbs, of course - every culture around the world has its favorites. Try some that bloom well on your balcony, and share your herbs with the pollinators!


Friday, January 24, 2020

Hops and Spice, Pipes and Paws: How Large a Tale will you Swallow?

Smoking in a Tavern: David Teniers the Younger
What image comes to mind, Dear Reader, when I speak to you of hops and spice, pipes and paws? For me it is one of those archetypal Dutch Tavern scenes of perhaps four centuries ago. The pipes of the smokers, the dog on the floor (proving that taverns in old Holland and restaurants in present day France are more civilized than we overly prissy Canadians), the jugs of spiced wine or the mugs of hopped ale were essential elements of a school of Pays Bas artists such as Matthijs Wulfraet, David Teniers the Younger, and Gerrit Dou (a student of Rembrandt).



Self Portrait - Gerrit Dou
Let’s start with pipes, shall we? Although pipes had been used for smoking substances such as hashish in Asia and the Middle East, it’s fair to say they were invented by Native Americans, who domesticated tobacco (Nicotiana rustica). Native Americans were also one of many groups that domesticated the Calabash Gourd (Lagenaria siceraria) for containers and food, but I find no records of their using gourds as pipes. Instead, South Africans seem to have placed a meerschaum bowl inside a curved calabash holder to create the classic calabash pipe, which became a fad when adopted by King Edward VII. This is now associated with Sherlock Holmes because it is a large but light pipe easy to clench between your teeth while delivering lines on stage. But, its use postdates the naming of the Pipevine, Aristolochia macrophylla, which I will sadly concede was named in recognition of its floral form matching clay or meerschaum pipes, not Sherlock Holmes’ calabash.


The big-leaved pipevine was commonly planted in North America a century or two ago, to shade a porch or verandah and give partial privacy. The large green leaves grow exuberantly and the peculiar fly-pollinated flowers provide sculptural interest. The leaves drop in the fall, allowing winter light to reach the porch.

But it’s not for its fly pollinators that I recommend this native vine to gardeners. Instead, its third merit to me is the fact that its leaves are the sole food the caterpillars of the beautiful Pipevine Swallowtail, Battus philenor, will eat.

Battus philenor. John Abbott, 1797
There are many pipevine species in North America and the Pipevine swallowtail likes all of them. Pipevines make a toxin, aristolochic acid, that deters herbivores. But the swallowtail caterpillars take it up and store it, the same way monarch caterpillars store cardiac glycoside from milkweed leaves. The adult swallowtails also taste bad to birds.

Around the world there are many swallowtail species whose caterpillars eat pipevine plants, and share the unpalatability to birds, but the Pipevine swallowtail is our only member of the group. But although it is relatively rare, you will see other swallowtails and unrelated butterfly species that mimic the Pipevine swallowtail. This is an example of what is called Batesian mimicry, where the mimic species gets the benefit (avoiding being eaten by birds) without the cost (methods to handle and store the toxic compounds). The Viceroy butterfly is a Batesian mimic of the Monarch, and the Spicebush swallowtail is a mimic of the Pipevine.

So, from pipes to spice we go!

Spicebush swallowtail - Benny Mazur, CC by SA 2.0
Several native shrubs have the common name “Spicebush”, but here we’re interested in Lindera benzoin, which gets the common name from the aromatic fragrance of its leaves. Lindera grows in
partial tree shade but blooms more abundantly early in spring if it gets some sunlight. The dainty yellow-green flowers don’t make a huge show but are pleasant when winter is ending. This native Carolinian forest shrub should be used more in our parks and ravines, so we can enjoy the Spicebush swallowtails that will come to it.

I’m writing this during the winter holiday, when of course spiced wine has been popular since the time of the Romans. So I can’t resist a spicy diversion. In 1,390 a mediaeval cookbook (by "the chief Master Cooks of King Richard II") gave this recipe for Ypocras: “Pur fait Ypocras …grinding together cinnamon, ginger, galangal, cloves, long pepper, nutmeg, marjoram, cardamom, and grains of paradise ("spykenard de Spayn", rosemary may be substituted). This is mixed with red wine and sugar”. I have read of this drink as “hippocras” - after steeping the spices in the sweetened wine for a day, the spices are strained out through a conical cloth filter bag called a manicum hippocraticum or Hippocratic sleeve (originally devised by the 5th century BC Greek physician Hippocrates to filter water).

"...we will discuss your affairs this very afternoon,
over a Christmas bowl of smoking bishop, Bob!"
Ebenezer Scrooge offered Bob Crachit a variant on hippocras called smoking bishop which was popular in 19th century England.




But what are we to do if we want native tastes in our holiday drinks? If you are lucky enough to have a male and female spicebush plant, the berries from the female can be used as spice. If you don’t have berries, the twigs and leaves can be steeped to make a tea. When my bush is bigger, I shall make this and call it “swallowtail tea”!






Hildegarde v. Bingen,
by W. Marshall
Some people enjoy hopped ales more than spiced wines. The seed clusters of the hopvine have been used in beers in Germany at least since renowned herbalist, mystic, abbess, and composer Hildegarde von Bingen wrote of them in the 11th century AD.

Giant Swallowtail near Ottawa - Gordon Robertson
When Europeans arrived here, they found shrubs and small trees whose seed clusters looked just like hops, and named them Hop Trees (Ptelea trifoliata). They grow wild along the Lake Erie shore in places like Point Pelee and Turkey Point parks, but with climate warming now survive Toronto winters. The seed pods are more decorative than the flowers, but I want to see them in our cityscape because the caterpillars of our largest butterfly, the Giant Swallowtail Papilio cresphontes eat the leaves. I wrote about hoptrees and giant swallowtails last fall.


I’ve taken us from pipes to spice to hops, with some deviations on the way. But what about paws? Admittedly, I am dreaming about getting a puppy in the new year, but here I’m thinking of the delicious and underused native Carolinian fruit tree, the Pawpaw or Asimina triloba. Pawpaw is now being grown in Toronto by connoisseurs who value the wonderful fruit. It fits into this article because of the beautiful native Zebra swallowtail  butterfly, whose caterpillars eat only pawpaw leaves.
Pawpaw flower - Krzystof Ziarnek CC-by-SA 4.0

I first saw these  lovelies during my two year exile in Virginia. The Palace of Neurons where I worked had large grounds running down to the Potomac River. In the moister soil near the river, Pawpaws grew in abundance as an understory tree. That’s plant geek for “grows OK mostly in the shade of big trees”. Pawpaw trees are very rare in Carolinian Canada, but we know our indigenous peoples used the fruit, because there are little-known groves of pawpaw trees next to some of the canoe trade routes inland from Lake Erie. In the spring, male Zebras patrolled streams leading to the Potomac Pawpaw groves, looking for newly emerged females. In summer, second brood adults perched on blue pickerelweed flowers (Pontederia) in the
Zebra Swallowtail - Clement Kent, CC by SA 3.0
ponds.

Given the delicious fruit and the spectacular butterfly, we definitely needs more “paws” in the ravines running down to High Park and in partly shaded places in our gardens.

There are two gardening notes to the pawpaw, though. It needs to be cross-pollinated so two genetically different trees should be planted within half a block or less of each other. And, it suckers from root runners. My trees do this but I find pruning the suckers at ground level once or twice a year controls them nicely. For a very nice dive into pawpaws, go here.


So, Dear Reader, that’s my tale: of Hops and Spice, Pipes and Paws.

Clement Kent

p.s. if you missed the previous post on Project Swallowtail, please give it a look. Project Swallowtail will be increasing the host plants above in order to have more of these beautiful butterflies.

Project Swallowtail!

Giant Swallowtail - Gordon Robertson
Today  it's my pleasure to pre-announce Project Swallowtail!
Zebra Swallowtail - Megan McCarty
This initiative to increase pollinator habitat in a large chunk of downtown west Toronto is led by WWF Canada in collaboration with many other groups, including my own Horticultural Societies of Parkdale and Toronto.






Blue dots on the map show just some of the gardens and Block Ambassadors already included.


Kathy's Garden, Stanley Park - Clement Kent
What are we going to do? Simply, we're going to help your block get a much higher density of pollinator-friendly plants over the next several years, with the goal of greatly increasing pollinator numbers and health. We want to do this in a way that allows birds, butterflies, and bees to move
freely for park to park and home to home. And, we'll be using some locally rare but very visible species such as the swallowtail butterflies shown above to make it easy to see when your block has become a hotspot of pollinator diversity.

LEAF Young Urban
Forest Leaders
We're also going to involve local kids and young adults in several ways. Mobile apps to help them identify plants and pollinators will be rolled out, with awards going to young pollinator experts.

Perhaps your block will become part of a neighbourhood where collaborator LEAF helps young naturalists learn about, map, and plant an urban forest?

Or maybe your or your neighbours' kids will go to High Park to learn about native plants and animals from H.P. Nature?

Block Ambassadors

Would you like to help us enrich your block for pollinators? We need Block Ambassadors! You don't need to be a gardener or a naturalist - just someone who likes talking with neighbours and promoting this project. We'll ask you to donate a few hours a month of your time to helping your neighbours get the plants and the help they need. You can reach us at clementfkent@gmail.com [this address will change very soon now!] See our map of ambassadors in your vicinity.


Collaborators:




Tuesday, November 26, 2019

Which flowers attract the most pollinators?

People often ask me "Which plants are best for pollinators?" There's no perfect answer, but I usually urge people to plant native perennials. But, is this right from the BBB (Birds, Butterflies, and Bees) point of view?

Professor Christina Grozinger
The perfect pollinator plant depends a lot on where you are planting it. A 20th floor balcony demands different choices than a back yard flower bed.  Experienced gardeners are good at helping you decide which plants will thrive in your location, but when we throw in the BBB perspective there is simply less expertise out there.

That's why it's nice to report that a number of pollination scientists have actually tested this. No one study covers the entire range of horticultural conditions but we can piece together a pretty good set of answers by looking at half a dozen papers published this decade.

I started off down this winding garden path by reading a recent article from the University of Pennsylvania titled "More Than Meets the Eye? The Role of Annual Ornamental Flowers in Supporting Pollinators". This is an open source paper (yay, authors!) from the lab of Christina Grozinger, a well respected pollinator biologist.

Emily Erickson
I was interested in this article because it looked at annuals, which are much more likely to be found in say a window box or balcony planter than perennials. Emily Erickson, a Ph.D. student in Christina's lab, went deep rather than wide. That is, instead of looking at 25 different species of ornamental annuals, she looked at just 5 species (Alyssum, Egyptian Starcluster, Lantana, Marigold, and Zinnia) but she evaluated 5 different strains of each species. This is really important because plant breeders don't usually select for things important to pollinators: nectar and pollen. Instead breeders look for color, size, and length of bloom. Some ornamental strains of common annuals are literally castrated - they provide no pollen to avoid mussing up your flower arrangements. Not so good for many pollinators!

By looking at many popular strains of some of the most often recommended annuals for pollinators, Emily was able to say not only which species of annual attracted the most butterflies, bees, and birds but also whether it matters which strain you find at the garden center. The short answer is yes, it very much matters.

Here are the 25 ornamental annuals Emily Erickson tested for attractiveness to pollinators:
Erickson et al 2019, Figure 2. Environmental Entomology. Copyright © 2019, Oxford University Press

Could you pick the best BBB plant by eye? The results are surprising. The most attractive strain, by number of pollinator visitors, was Alyssum 'Snow Princess', and in second place Alyssum 'Frosty Knight'. Snow Princess had more than three times as many visitors as the average strain tested.

Why? Well, one factor is that those two Alyssum strains have been bred to be sterile - they don't set seed. This means sterile flowers keep on providing nectar and pollen much longer than a flower which has been pollinated and turns its energies to setting seed. Florists and garden show exhibitors know this trick - a mesh bag or old stocking tied over a spike of delphiniums or larkspurs will give many more flowers in bloom for the vase than a flower spike in which pollinators have had access.

The other three Alyssum strains are all fertile and had average numbers of visitors, except for 'Wonderland Deep Purple', which had the third lowest visitor count of the 25 strains. Strain matters!

"Egyptian Starcluster" is a more awkward name than Pentas, the scientific genus name. This species is hyped as great for pollinators, but had the lowest average visitation over the 5 strains, as well as the lowest and second lowest strains. I'd avoid it! Here are quotes from three different websites:
"Pentas is one of the best pollinator friendly plants you can grow."
"Colorful pentas, also known as Egyptian starcluster or star flower, are one of the best choices to attract pollinators like butterflies and hummingbirds to your garden."
"Vibrant blooms are a magnet for pollinators."
Zinnia 'Peppermint'. Clement Kent, CC-by-SA 3.0
 Emily Erickson noted not just the number of pollinators but the kinds as well. Alyssum had mostly bees and flies visiting, while marigolds had bees and some butterflies. Lantana had almost entirely butterfly visitors, while Zinnia had a good balance of types of pollinators. Please note that among Zinnia strains, you're best off with those that are not too doubled. In the picture from my back porch this summer on the left,  are three blooms from the seed strain 'Peppermint'. The one on the right is so doubled that the actual florets (the little yellow bits in the center) are covered up. That flower may be nice to our eyes but it will get no pollinators. The one in the middle is what you are aiming for.



Monarch on Zinnia. Clement Kent, CC-by-SA 3.0
If you buy zinnias at a store, look for a broad central region with actual florets, such as the one on the right from my garden. These really do get a great stream of butterflies, bees, and hummingbirds.

Well, it's time for me to help with dinner. Next time I blog, I'll look at scientific studies of pollinators on perennials and herbs, with some delicious advice for balcony gardeners.