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Good Plant / Bad Plant

by Tim Kennelty

Taghkanic resident, Tim Kennelty is a Master Gardener and Master Naturalist volunteer through Cornell Cooperative Extension, and is the co-host of Cornell’s weekly Master Gardener podcast, Nature Calls: Conversations from the Hudson Valley.

Column #6 – Asters and Tree-of-Heaven

It’s that time of year when some plants are waning and others are just beginning to show their beautiful blooms. If you’re supporting pollinators, you’ll want have plants that bloom throughout the season, even into October. Our good plant for this month is an autumn workhorse and our bad plant may look pretty right now, but beware!

In this edition we have two “A” plants – one good and one bad. The good plant is the beautiful and beneficial late blooming Aster, and the bad plant is one that some people think is beautiful, but is really a nasty character – Tree-of-Heaven or if we’re talking Latin – it’s “A” name is Ailanthus altissima.

So, let’s start with the good plant, the genus Aster. I must confess that what we think of as our native asters like the commonly called New England or New York fall blooming asters are no longer in the botanical world referred to as “Asters.” Every five years the International Botanical Congress meets to update the naming nomenclature for plants. A few years ago they decided that Eurasian and American asters were different enough to be classified with different genuses. Thus the roughly 180 American or New World asters were forced to find new names under different genera. I tell you this only because if you go to the nursery looking for Asters, you’re may need to look under their Latin name Symphyotrichum. Don’t despair though because most nurseries still refer to these beautiful plants as asters, and for simplicity sake, so am I.

Ok., enough about naming. Why am I even talking about Asters? It’s because they are such great garden plants. If you want vibrant color in shades of purple and pink and even white and you want to support pollinators, you really should think about adding asters to your garden. Both New England and New York asters are native to the Northeast and thrive in a wide range of growing conditions. In general they prefer full sun and well drained soil and are relatively easy to grow. New England Asters have full, plump blooms and woody stems, while New York Asters have smooth leaves and thinner stems.

There are many, many cultivars and sub-categories of asters ranging in height from one to six feet. Most, however, are perennial, have daisy-like, colorful flowers and bloom anytime between August and October. I’ve even had asters in my garden blooming at Thanksgiving. Asters can be nibbled on by rabbits and deer so you should keep that in mind when siting them in your garden. Some of my favorite cultivars are: “Purple Cloud,” “Kickin Carmen Red,” and “Alma Potschke,” but there are countless others and I think it’s safe to say there’s a cultivar for every taste.

Besides being beautiful, asters attract and support many late season pollinators in the garden. And in the winter, don’t cut them back, as they provide food and shelter for many bird species and small mammals. They’re even a host plant for Painted Lady and Pearl Crescent butterflies. In fact, Doug Tallamy includes asters on his “Keystone Species List” – which is a group of plants that are the most important for supporting wildlife. So, if you need some beautiful late season color and you want to be kind to the birds and bees, plant some asters in your garden.

Now for the really bad actor – the inappropriately named Tree-of-Heaven or Ailanthus altissima. And of course, when I say “bad actor” it’s not the plant’s fault that it is an invasive pest in our area. For any invasive, non-native plant some human brought it to our shores thinking it was beautiful, a food source or had medicinal value. Tree-of-Heaven which is native to China was first introduced in Philadelphia in the late 1700s. Thereafter, it was widely planted in urban areas from New York City to Washington, DC. At the time, it was thought to be an attractive ornamental tree that was fast-growing and tolerated a wide variety of conditions. By the early 1900s attitudes towards this plant began to change because of it’s weedy nature and foul odor. Today it is thought to be a highly invasive plant. More about that in a minute.

Tree-of-Heaven is a fast-growing deciduous tree that can reach heights of 80-100 feet. Its leaves have a central stem with multiple lance-shaped leaflets on either side. When crushed the leaves have a strong, offensive odor. Some describe it as rotten peanut butter. This tree’s leaves closely resemble those of two natives – black walnut and sumacs. I have all three on my property and it can be confusing. The main difference is that both black walnut and sumac leaves are serrated while tree of heaven leave margins are smooth. And when in doubt, take a sniff for that foul smell.

Like many invasive plants, Tree-of-Heaven has multiple reproductive strategies. Female trees can produce more than 300,000 seeds that are wind dispersed. Individual trees spread through aggressive root suckering. A new sprout can emerge as much as 50 feet from the tree. In addition, leaves, roots and bark of the tree contain allelopathic chemicals which inhibit establishment of native plants. So, as you can imagine this plant can be highly destructive to native ecosystems, pushing out valuable plants and often forming monocultures. This plant has one more bad trait and that is that it is primary host of the Spotted Lantern Fly. This is a highly destructive, invasive insect which is on the verge of establishing itself in our area.

So, if you identify Tree-of-Heaven in your yard, what should you do? If you have small shoots, they can be pulled when the soil is damp, but make sure you remove all of the underground shoot or the plant will resprout. For larger stands cutting or mowing is usually ineffective because the plant will quickly produce a large number of resprouts. For effective control you will probably need to use herbicides. As always, use caution and read all labels and follow instructions. I’m including links about this plant with more information on identification and control.

That’s it for another edition of Good Plant/Bad Plant. And as always, if you want to support wildlife in your yard, plant natives.

Note that this will be the last edition of Good Plant/ Bad Plant for the season. GP/BP will return in the Spring with more plant heroes and villains. In it’s place will be a new column about print and online resources for gardeners. So, be on the lookout in October for the first edition of Tools of the Trade.


Tree of Heaven

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