Friday, December 17, 2010

Under the Norway Maple

One of the most common trees in the residential setting is the Norway Maple, Acer platanoides. It was first introduced into the United State in 1756 by John Bartram. It is well adapted to the climate in the Northeast and grows well under a wide range of growing conditions, making it a preferred tree in urban and suburban landscapes. It’s tolerance of for almost any environmental condition, ability to grow in the shade, prolific seed production and overuse in the landscape has led to this becoming a dangerously invasive species in the Northeastern US.

Working in residential landscapes I often encounter the difficulty of working around this species. Its dense shade and greedy roots that suck moisture out of soil make it difficult to underplant. While many consider the Norway Maple as allelopathic (producing compounds that retard the growth of other plants), there are studies that indicate that this is not the case. (One study found no experimentally measurable allelopathic effects from Norway Maple.)  I think the problems encountered under a Norway maple are mainly due to the shade it casts and the dense network of roots that scavenge moisture and nutrients from the soil.

Norway Maple stump 6 years after a native species
restoration at Mount Auburn Cemetery

This photo shows the best method for dealing with a Norway Maple. Despite my disdain for this tree, I have not taken that step on my own property, yet. Since there is not another tree in the area to provide shade around the house for the hot afternoon sun I am hesitant to open up the canopy that much. Instead I have been exploring which native plants will grow under its canopy.

To get some ideas, I tried to learn about what grows the natural forest community along with Norway Maple in its native range (Europe and Asia). I thought I could find native equivalents to those European species. This tree is naturally found in mesic deciduous forests and mature riparian communities. While I did not find a definitive description of the other plants in this community (I’m sure that information is out there) I did get some clues from a site on the Plant Formations in the Central European BioProvince.  One shocking conclusion jumped out.

Many of the perennials and shrubs that grow in forests along with the Norway Maple are also invasive, or have tendencies toward invasiveness, in North American forests. These include goutweed (Aegopodium podagraria), fig buttercup (Ficaria verna), Tartan honeysuckle (Lonicera tartarica also L. xylosteum), yellow archangel (Lamium galeobdolon), and lily-of the valley (Convallaria majalis).  So I would be hesitant to recommend any new non-native species with the possibility of making a bad situation worse. However there were some others that are better behaved such as sweet woodruff (Galium odoratum), European ginger (Asarum europaeum), Siberian squill (Scilla sibrica), Tartan dogwood (Cornus alba) and fumewort (Corydalis solida) and some really neat plants like common hazel, Corylus avellana (from which comes ‘Harry Lauder’s Walking Stick’ ). 

In my own testing, I have been selecting native plant species that are tolerant of dry shade. So far I have found a number of natives that survive but do not flourish. It seems to be a general trend that all plants grow smaller and slower in that environment. However, there are a few that are more than holding there own. My plant list is as follows:

Smooth Aster and Showy Goldenrod,
both about 1/2 size of those
in other parts of the garden
American Bellflower (Campanulastrum americanum), American Pennyroyal (Hedeoma pulegioides), Smooth Aster (Symphyotrichum laeve), Heartleaf Aster (Symphyotrichum cordifolium), Virginia Creeper (Parthenocissus quinquefolia), Wafer Ash (Ptelea trifoliata) , Wild Bleeding Heart (Dicentra eximia), Witchhazel (Hamamelis virginiana ).

Holding their own:
Male Fern, still green after a couple of frosts.

Male Fern (Dryopteris filix-mas), Christmas Fern (Polystichum acrostichoides), Rosey sedge (Carex rosea), Alumroot (Heuchera villosa), Barren Strawberry (Waldsteinia fragariodes), Hairy solomon’s seal (Polygonatum pubescens), Largeflower bellwort (Uvularia grandiflora), Rosinweed (Silphium integrifolium), Showy Goldenrod (Solidago speciosa), Twinleaf (Jeffersonia diphylla), and Possumhaw Viburnum (Viburnum nudum).  This particular Viburnum was selected to improve pollination of the 'Winterthur' Viburnums nearby.

Promising, but still early:
Allegheny vine (Adlumia fungosa), Black Huckleberry (Gaylussacia baccata), Black-eyed Susan (Rudbeckia hirta), Inland Sea Oats (Chasmanthium latifolium), Lowbush Blueberry (Vaccinium angustifolia), and Pennsylvania sedge (Carex pensylvanica).

Failures, faded away or died outright:
Canada Mayflower (Maianthemum canadense), Fetterbush (Leucothoe fontanesiana), Foamflower (Tiarella cordifolia), Green and Gold (Chrysogonum virginianum), and Squirrel Corn (Dicentra canadensis). (When I moved the Leucothoe to a different shady location, without the root competition, it perked up after a couple of weeks.)

Plants that should work, planned for next season:
Labrador violet (Viola labradorica) and Maple-leaf viburnum (Viburnum acerifolium),

In addition to using plants that are strong competitors that can get their share of moisture there are some maintenance practices that will help the understory plants. Limbing up and thinning the canopy to let in more sunlight has helped a lot. Also, new plants should be irrigated deeply to get them established as well as under droughty conditions (mid-summer). Returning leaf mulch to the understory area helps to build the soil.

I’d like to hear what other natives have worked for you under Norway Maples, or ones that have failed desperately.


Heather said...

Great post.
We had a 'Crimson King' Norway Maple in our yard (not as large as yours) that we cut down right away. I have been removing 4-6 foot saplings in the rest of the yard from this tree.
I have since planted Nannyberry Viburnum, Dwarf Bush Honeysuckle (Diervilla lonicera), Zig zag Goldenrod and a small Hackberry tree in around the stump.
I love Maple Leaf Viburnum - had some when we lived on the east coast. I think you might have luck with this next year. I just did a post on Pennsylvania sedge which you mentioned. Also look for the other wood sedges that are tolerant of dry soils.

Laurrie said...

You didn't mention one species that does well under a Norway maple: utility boxes. That's what I have smack under mine (which is a Crimson King to boot, and there are hundreds planted around my neighborhood, all dark purple monsters). Your studies are fascinating! I am enjoying your experimental method for figuring out what will work under this tree, as I have the challenge of planting something under mine. (Not native, but very dry-shade tolerant are epimediums... )

THB Farm (Ellen S) said...

Curtis, good experiments for those who are unable to remove their Norway Maple, which is really the only solution that makes sense, but may not be affordable. We had 8 of these (street trees) on our last property and I was sooo frustrated with how their roots will travel far and wide for any decent soil so that it can suck the moisture and nutrients from it. Every year I would pull hundreds of the seedlings out from under the shrubs and gardens...probably why I ended up getting tendinitis in my wrists! In the end, we had to move to get away from those norway maples (just kidding) but to this day I wish we had removed them all. Interesting that the norway maples are just about the only plants that still survive there.

kathy said...

thanks for the information. i plan to try the plants you claim are spreading. hopefully they'll work for under my norway maple too.

kathy said...

thanks for the helpful and hopeful information. i plan to try some of the plants you mention that are spreading under your tree. hopefully they'll work for me too.

Curtis said...

I just added some Canadian Anenome to the area under the Norway Maple. I have heard that it has been succussful for others. It is known to be a vigorous spreader.

Anonymous said...

This is very helpful. In our own yard the Woodland Aster is prolific near the maples, pennsylvania sedge grows right over the roots and these plants all seeded themselves. We planted a Redbud on the southside of a large Norway Maple under its branches. It is actually doing very well. A Rhodedendron planted very small within the shade of 5 Norway Maples is growing. Sadly, tiarella, hobblebush, Queen of the Prarie and Black Eyed Susans all planted on the south side also died within a season.
We are experimenting with Celadine Poppy and Mayflower this year.

Anonymous said...

Thanks for posting the comments. I have a yard which has natives and non-natives, and Norway Maples I inherited. I am cutting most down, but trying to grow a shade garden under one in a somewhat moist area. The area gets runoff from my neighbors yard, my driveway and downspouts.

1. Hydrangea serrata - non-native. I got these as root divisions, and these are doing great about 4 ft from the trunk.
2. Hydrangea macrophylla - not doing so great. Small and not flowering.
3. Tiarella - straight species, or sugar and spice. I forget. Small but alive about 4 ft from the trunk.
4. Mountain laurel - doing really well about 3 feet from the trunk! It was dying from a fungal disease in the old location under pines, but it is green and healthy looking under the evil norway maple. go figure.
5. Heucheras - Small but alive for several years 5 ft from trunk.
6. Impatiens pallida - I got these wild. Grow well under/near these maples as long as they get enough sun, and probably water.

7. Creeping jenny - nonnative and probably invasive, but it grows right up to the trunk.
8. Squaw Weed - grew about 3-4 feet from the trunk of the limbed-up crimson king ok.
9. Fleabane Daisy - Also wild and my FAVORITE wildflower which came w/ the property. I just sprinkled seeds. It grows right up to the trunk and doesn't even seem to need extra water.

Hopefully mine will continue to do OK. I've also planted christmas fern (under) and ilex opaca (nearby about...8ft away) in the shadow of the maple. I am also growing an itea virginica about 6 feet away, but agian...the maple is in the path of my runoff, and I've made it into a somewhat rain/shade garden.

I do occasionally throw organic fertilizer or planttone in the area, and I use pine bark mulch.

Hopefully my experience will be helpful!

I was searching because I have a maple in a full-sun area, but I need evergreens around it for privacy. I may have to end up cutting the thing down.

Curtis said...

Thanks for sharing this information. That is a pretty nice list of plants. I planted a Norway Spruce under my Norway Maple when I moved in 18 years ago. In that time it grew very slowly to about 12'. It started to take off after the Maple canopy was thinned out. There may be some Norway Spruce cultivars that could fit you evergreen needs, you just need to manage their growth.

Anonymous said...

Great work, thank you for sharing. We have a norway maple in front. The spring natives bloodroot and trillium are happy. Snow-on-the-mountain thrives even a few feet away (but it can really take over). oakleaf hydrangea is growing well on north side of the maple.

Good Oak said...

I'd love to hear an update of what is working well 3 years later... just a quick list could be very informative!

Curtis said...

We moved last fall, but as of that time I can give a brief update. The Waldsteinia and and Rosey Sedge were overgrown by other plants, especially the Virginia Creeper. The Adlumia and Gaylaccasia did not continue either. The blueberries have survived, but don't get enough light to produce fruit. I did find that the Chrysogonum did come back in a different location under the tree where it has less competition. All the other plants list have continued to do well.

Julia Bunn said...

Very grateful for this list and your experience! Its always such a temptation to say down with that Norway but prudence would advise otherwise. Just get the new Trees growing so when the right time comes, then. Glad to get acquainted with your Blog. The Spirited Gardener

Peter Caesar said...

I've found that a prostrate cotoneaster, a creeping euonymus and a hemlock shrub have historically done well in a bed on the north side of my house that has always been dominated by the roots of a nearby Norway Maple.