Clethera Alnifolia
Clethera alnifolia, summersweet

Smithsonian Gardens’ Horticulturist Alex Dencker shared suggestions on native shrubs that make excellent substitutes for common, non-native landscape plants and help you garden with local ecology in mind.

Webinar video

Useful websites and resources

For information on pesticides, herbicides, and insecticides please contact your local Extension Agent. They are familiar with local guidelines.   

Q&A from the webinar

 Please list some deer-resistant native shrubs. 

  • Yaupon – Ilex vomitoria 
  • Fragrant sumac – Rhus aromatica 
  • Scarlet buckeye – Aesculus pavia 
  • sweet pepperbush – Clethra alnifolia  
  • eastern sweetshrub – Calycanthus floridus  
  • devil’s walkingstick - Aralia spinosa 
  • red cedar – Juniperus virginiana 
  • American holly - Ilex opaca 
  • spicebush – Lindera benzoin 
  • sweet bay magnolia – Magnolia virginiana 
  • wax myrtle – Morella cerifera 
  • red chokeberry – Photinia arbutifolia 
  • winged sumac - Rhus copalinum 
  • black elderberry – Sambucus canadensis 
  • black haw – Viburnum prunifolium

Define heavy clay. 

The Pennsylvania State Extension has a great webpage that explains different soil types: https://extension.psu.edu/soil-quality-information .  Personally, I would first look at the soil. Grab a handful. If it stays as a sticky lump rather than crumble in your hand the clay content is pretty high.  If the soil is uniformly the same color throughout that is another good indication of high clay content.   

Your thoughts on improving the soil vs. planting natives in native soil? I’ve heard that natives do well in native (unamended) soil. I’m having a hard time imagining that my “native” dense, heavy clay is a hospitable environment for plant growth. If soil should be amended, what amendments should be used, and how much? Are there alternatives to homemade compost, which we never seem to have enough of?
While it is true in principle that native plants can handle clay –plants indigenous to a region are adapted to the soil and weather conditions there — soils in many suburban and urban gardens are no longer “native” due to compaction or construction work that’s altered the land.  Heavy clay soils don’t moderate conditions very well. When they are dry they become rock-hard and tough to work with and if too wet they absorb water slowly and hold it for a long time. Plants that thrive in clay, including many natives, are tremendously hardy, and their root systems are strong enough to break through clay soils.

Look at the lay of the land and make sure the planting area will not be continuously inundated with water and that it slopes properly to allow water to evacuate if needed.

  • When you dig, the “hardpan” is the biggest concern – the depth that your shovel has not reached.  Plants like native grasses will penetrate the hard, untouched layer.  Panicum virgatum switch grass is a good example.   
  • When you plant, mix in organic matter. I add fine pine mulch (25%) mixed with compost (25%) and combine them with the garden’s soil (50%).
  • Some native shrubs that tolerate heavy clay soil: 
    • Black Chokeberry Aronia melanocarpa 
    • Red Twig Dogwood Cornus sericea  
    • Common Ninebark Physocarpus opulifolius 
    • Common Elderberry Sambucus canadensis
  • Native perennials that tolerate heavy clay soil are just as varied and diverse: 
    • Black Eyed Susan, beebalm, switchgrass

What native shrubs need a male and female plant?
Hollies and blueberries are the two best examples of plants which require male and female plantings.  Consult your local county extension service for a list of others.  

When is the best time to trim winterberry and other fruiting shrubs?
Certainly, pruning at the wrong time will disrupt flower and berry production.  Remember if the plant flowers on old wood to prune as soon as the flowers fade.  This will give the plant plenty of time for new growth which promotes new flowers in the spring.  I think the crux of your question may be “How to balance pruning with fall berry production?”  I would recommend selecting 1/3 of the shrub’s old stems or canes to remove each year.  You will always end up pruning off some flowers or berries, but this practice will limit the loss of both.

When is the best time to prune ninebark?
This shrub should be thinned regularly. Prune as winter is ending until early spring. 

What are the pollinator benefits of species vs. cultivars?
When it comes to pollinators the straight species is always superior.  Cultivars may have more interesting flowers, more intense or different colored leaves, and bigger berries that make them more attractive to humans, but they are also more unpalatable to wildlife.  However, the more “attractive” cultivars may increase awareness and use of native plants and encourage conversations about the importance of native plants.  

Please list some native evergreen shrubs 

  • Inkberry – Ilex glabra 
  • Mountain Laurel – Kalmia latifolia 
  • red cedar – Juniperus virginiana 
  • American holly – Ilex opaca 
  • sweet bay magnolia – Magnolia virginiana 
  • wax myrtle – Morella cerifera 

 Is there a native replacement for butterfly bush?  

  • New Jersey tea – Ceanothus americanus 
  • Buttonbush – Cephalanthus occidentalis 
  • sweet pepperbush – Clethra alnifolia 
  • spicebush – Lindera benzoin 
  • Virginia sweetspire – Itea virginica

Do any native shrubs tolerate flooding and shade?
Lots of shade and water is a little tough: try some of the native shrubby dogwoods. You might also try Virginia sweetspire – Itea virginica.   

 What is the difference between chokecherry and chokeberry?
Chokeberries, also known as Aronia, are multi-stemmed shrubs with white flowers, red or black glossy berries, and great red fall color. It is a tough, dependable plant with three-season interest, especially in shady, wet sites.  It works well in a naturalized landscape or garden. Chokecherry is also known as Prunus virginiana and is one of our native cherry trees.  It’s great for bees and is a larval host for loads of butterfly and moth species.  It has white flowers and grows up to 30 feet.   

 Are there any chemical treatments to deter deer?
Many deer repellents are available at your local garden center.  Basically, they all have the same ingredients: dried blood, garlic, and rotten eggs.  The dried blood invokes the fear of predators and the others simply smell and taste unpalatable.  They all work pretty well and last longer than I thought they were going to, I would guess about three months. To make it through the growing season you might need to reapply in September.   

Which plants have toxic berries?
Many plants in our gardens produce foliage or berries which are toxic including several members of the buttercup family, Ranunculaceae, that often have showy flowers like buttercup, clematis, columbine, delphinium, and hellebores. Native holly shrubs are toxic and not good to eat in any way – foliage, berries or woody stems.  

Why is it so hard to grow Kalmia?
Mountain Laurels like moist yet well-drained soil.  Look at the lay of the land to make sure the planting area is not going to be endlessly swamped with water and that it slants properly to allow water to evacuate in a reasonable amount of time.  Adding fine pine mulch (25%) mixed with compost (25%) to your garden’s soil (50%) adds acidity and organic matter. The mulch is also ‘chunky’ which provides air spaces for better drainage.   

What causes rust on serviceberry and how do you prevent it?
Serviceberries are susceptible to a few fungal diseases. Wet spring weather makes serviceberry susceptible to rust. Cedar-serviceberry rust affects twigs, buds, fruit and foliage.  The rust disease requires two hosts, a juniper (eastern red cedar) which is not damaged by the rust, and a serviceberry (apple or hawthorn).  Nothing can be done once the plant displays signs of the pathogen.  The only way to prevent rust before it has a chance to occur is to remove junipers in the area or spray the serviceberry with an appropriate fungicide. Check with your local extension agent for the proper fungicide for your area. 

 What are some shrubs for slopes, formal gardens, and hedges?
Hollies, wax myrtle (Morella cerifera), bayberry (Myrica pensylvanica), many viburnums, fragrant Sumac (Rhus aromatica), native shrubby dogwoods (silky dogwood – Cornus amomum and red Osier dogwood – Cornus sericea). 

 What are the best plants for full sun, wet in winter, dry in summer? 

“Wet feet” in the winter is always a little tricky – however you might try some of these shrubs:   

  • black chokeberry – Aronia melanocarpa 
  • buttonbush – Cephalanthus occidentalis 
  • elderberry – Sambucus canadensis 
  • eastern ninebark – Physocarpus opulifolius 
  • possumhaw – Viburnum nudum 
  • St. Johnswort – Hypericum densiflorum 
  • silky dogwood – Cornus amomum 
  • spicebush Lindera benzoin 
  • swamp azalea – Rhododendron viscosum 
  • swamp rose – Rosa palustris 
  • wild raisin – Viburnum cassinoides 
  • winterberry – Ilex verticillata 

 SHRUBS for SUN 

  • Summersweet – Clethra alnifolia
  • Virginia sweetspire - Itea virginica
  • Dwarf Fothergilla - Fothergilla gardenii
  • Witch-hazel - Hamamelis virginiana
  • New Jersey Tea – Ceanothus americanus
  • Inkberry – Ilex glabra
  • Winterberry – Ilex verticillata
  • Chokeberry 
    • red chokeberry - Aronia arbutifolia 
    • black chokeberry – Aronia melanocarpa 
  • Fragrant Sumac – Rhus aromatica 
  • Viburnum 
    • arrowwood – Viburnum dentatum 
    • possumhaw – Viburnum nudum 
  •  Eastern Ninebark – Physocarpus opulifolius 
  •  Fringetree – Chionanthus virginicus 
  • Buttonbush – Cephalanthus occidentalis 

SHRUBS for SHADE 

  • Hydrangea  
    • wild hydrangea – Hydrangea arborescens 
    • oakleaf hydrangea – Hydrangea quercifolia 
  • Mountain Laurel –Kalmia latifolia
  • Highbush Blueberry –Vacciniumcorymbosum 
  • Silky Dogwood –Cornus amomum
  • Red Osier Dogwood –Cornus sericea
  • Rhododendron spp.
    • Coastal azalea – Rhododendron atlanticum 
    • Pinkster azalea – Rhododendron periclymenoides 
    • Swamp azalea – Rhododendron viscosum  
  • Allegheny Serviceberry –Amelanchierlaevis