by Tim Kennelty
Column #2 – Dogwoods and Garlic Mustard
Good Plant/Bad Plant is a monthly feature of the TGazette, focusing on two plants in each edition - one plant that is ecologically valuable and one plant on the other end of the spectrum that is invasive or a noxious weed.
It’s May so I’m focusing on what you might be seeing out there blooming either now, or later in the month. In this edition the good plant is actually a group of plants – the native dogwoods of the genus Cornus. And the bad plant, many people just consider a common weed, but it’s actually a really destructive invasive and that is garlic mustard.
So, as always I’m starting with the good guys, the dogwoods. Dogwoods include a large group of shrubs and small woody trees all in the genus Cornus. The genus also includes a group of what might be called sub-shrubs, fast growing plants that die down to the ground in winter and then sprout back in the Spring from buds at the base of the plant. Some of these like bunchberry can actually be used as ground covers. There are about 50 different species of dogwood and many are native to our area.
What almost all native dogwoods have in common is that they provide multi-season interest with attractive spring flowers, colorful berries in mid to late summer, devoured by birds, and often brilliant fall color. Growing conditions for dogwoods depend upon the species you are planting. Most people associate the term dogwood with the commonly named “Flowering Dogwood” or Cornus florida. This is a small to medium-sized deciduous tree, often used as a specimen, because of it’s beautiful white or pink spring flower bracts, colorful fruit and attractive fall foliage. This tree – which we can often be seen in the understory of our local woods – suffers from a variety of diseases and insect pests. However, there are quite a few disease-resistant cultivars. One of my favorites is ‘Appalachian Spring’ which is said to be highly resistant to anthracnose and powdery mildew. I have two in my landscape, and I have found them to be vigorous, beautiful and disease-free.
One of my other favorite native dogwood trees is Cornus alternifolia, often referred to as Pagoda Dogwood, because of its lovely pyramidal habit. This is a beautiful tree that can tolerate a good deal of shade, with small white flowers in spring and blue/black fruit in late summer. I have a Pagoda dogwood growing just behind my screened porch and in July I just sit and watch the wood thrushes, catbirds, and cedar waxwings devour the berries, usually in one day. In fact more than 35 species of birds eat the fruit of this tree.
And let’s not forget the dogwood shrubs. Like flowering and pagoda dogwoods, shrubs such as gray dogwood, silky dogwood, round-leaved and red twig or Redosier dogwood may be a bit more wild in habit and look, but they all have great spring flowers for pollinators, attractive and nutritious fruit for the birds and many are host plants for butterflies and moths. All of these are fairly easy to grow with best results in well-drained soil and part to full sun. One way to use dogwood shrubs in the landscape is to plant a grouping of different dogwood shrub species as a wildlife hedge that will provide multi-season interest for you, as well as food and shelter for the birds. So, do yourself a favor and check out native dogwood trees and shrubs…you won’t be disappointed.
Unfortunately, we also have a bad plant to talk about, and our bad plant for May is none other than the seemingly ubiquitous garlic mustard. Garlic mustard is a non-native invasive herb that has spread through much of the Northeast and Midwest causing significant ecological damage. Garlic mustard is native to Europe and parts of Asia and is believed to have been brought here in the 1860s as a food or medicine crop. It is a biennial, meaning that it matures in two years. The first year it appears as a short rosette and in the second year it grows a tall stock with small white flowers that quickly produce literally thousands of seeds before it dies in mid-summer. The plant has a distinctive garlic odor and can be foraged and eaten.
So why is garlic mustard so bad? Like many invasive plants, it can form dense stands, or monocultures, pushing out beneficial native plants. Garlic mustard is especially detrimental because it produces thousands of seeds that can be viable in the soil for up to ten years. It’s an allelopathic plant which means it produces chemicals that can inhibit growth of other young plants. And because most insects and mammals won’t eat it, this plant can quickly become dominant in a landscape.
One of the most effective methods, especially with smaller stands of garlic mustard is hand pulling the entire plant. This is best done in spring when the ground is soft and before the plant has produced flowers or seed. If the plant is already in bloom, I simply cut off the florets. Because garlic mustard is a biennial, once the plant has flowered, it will die. Pulling or cutting is a long-term process – I feel like I’ve been pulling garlic mustard in my garden since the beginning of time. But, it ‘s well worth it if you can gain some control. With larger stands, chemical controls may be considered. There are links to more information about this below. As always it’s best to know your foe.
So, get out in your garden and plant a dogwood or pull some garlic mustard. And remember, as a gardener, you can make a difference. if you want to support wildlife in your yard, plant natives.
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.
Garlic Mustard Links: