trees and shrubs – Maryland Grows

Invasive Ornamentals and Sterile Varieties

August 21, 2026Maryland Grows2 Comments

When it comes to landscaping, a huge decision-making point is what we find visually pleasing… and often what pleases us visually ends up being something we are not very used to seeing, meaning that we pick plants that seem more exotic to us so we can marvel at their surprising (to us) beauty. This is all good and nice, but the problem appears when we realize that many of those plants appear exotic to us because they are exotic to the region we live in! This means that if we select them to plant in our landscapes, we are actually adding to our environment species that are not necessarily native to where we live… which can have pretty drastic consequences. In today’s post, I want to talk about a potential solution that has fairly recently been proposed to the use of such plants: sterile varieties.

What’s the deal with exotic plants?

Although not all exotic plants will have negative effects on our environment, some of them do. Those that do are considered invasive species, and they can create a lot of trouble in our local ecosystems. Invasive plants tend to grow faster than other native plants, often overrunning the spaces they grow in, spreading very quickly, and eventually “choking” or outcompeting local species, which end up dying out and/or becoming unable to survive in the presence of the invasive plant. Some good examples of this behavior of invasive plants in Maryland are the Chinese and Japanese Wisteria vines and the English Ivy, all of which effectively cover trees and can eventually choke and pull them down to their death.

View of a forest with vines covering the tree trunks up into the canopy. — *In the Eastern USA, English Ivy does effectively take over forests. Photo: L. J. Mehrhoff.*

In Maryland, this issue has been recognized not just by ecologists, but also by lawmakers, who have started to regulate the selling of specific species to properly support the protection (and recovery) of our local plant communities. Among the most recent additions to these regulations are the ban on selling several bamboo species, English Ivy, exotic Wisterias, and several very invasive grasses (among other species). You can check the most up-to-date list of these species at the Maryland Dept. of Ag. website: Maryland Prohibited Invasive Plant Law and Regulations. The Maryland Department of Natural Resources also hosts a website with a lot of information about exotic species (plants and others): Invasive and Exotic Species in Maryland

So what to do if we love the plants but do not want them to spread?

Ideally, if we do not want to harm local habitats, the best decision is to refrain from planting invasive species, because they are REALLY hard to properly control and prevent their spread (especially when there is bird-mediated fruit dispersal or stolon-mediated dispersal).

The forest in spring with many mature trees and Barberry invading the understory and dominating as the ground cover — *Barrberry dominating the understory in a wooded setting. Photo*: *Leslie J. Mehrhoff, University of Connecticut, Bugwood.org*

Bright red berries the shape of water drops hang along barberry branch. — *Barberry shrubs produce many berries that birds and wildlife eat then distrubute. Photo:* *Chris Evans, University of Illinois, Bugwood.org*

An alternative, however, is the selection of varieties that are unable to spread because they are sterile or do not have proper structures to do so. These are varieties that exist for some ornamentals/exotics, and that are in some cases exempted from the regulations that I was mentioning above. Some examples are non-invasive bamboo varieties, some Berberis cultivars (e.g., varieties “Lemon Glow”, “Crimson Cutie”), and even some almost-sterile Buddleja cultivars (e.g., “Flutterby”, “Lo and Behold” varieties developed by several University programs). A note on some of these cultivars is that although some of them are labeled “sterile”, they may or may not be fully sterile. Some of them have indeed been shown to, in some cases, produce some fertile offspring (although way fewer than their fertile counterparts!).

A green field with a forest line in the background. Purple wisteria vines are growing up many trees and shrubs, toppling one over. — *Invasive Wisteria invades forests, vining themselves onto trees, pulling them down and eventually outcompeting and often killing them. Photo: M. Bakacs.*

How to go about these decisions?

Generally, when considering exotic ornamentals for our green spaces, it is worth making it a practice of first informing ourselves about their potential for invasiveness. Then, if the potential is there, another good practice is to look for potential alternatives (e.g., do we really need to plant that specific plant?, are there less-harmful varieties?, are there native alternatives that can be planted instead?, can we properly contain the plant if it spreads?).

To make these decisions, a good tool to consider is the NC Extension Gardener toolkit, where species and varieties are listed and can be filtered out by (among other traits) their potential for invasiveness/weediness. The Maryland Invasive Species Council has also put together a list of species that have invasiveness potential (independently of regulations) and are thus of concern. A new tool from the University of Maryland Extension Maryland Native Plants Project can help you search and filter for native plants, so you can potentially choose a native plant which will suit your needs and benefit our eco-system: Maryland Native Plant Finder tool.

By Anahí Espíndola, Associate Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

Think Spring! Gardening Projects to Start in February

February 24, 2026February 25, 2026Maryland GrowsLeave a comment

A tree in front of a house set in a snowy landscape featuring a broken branch due to ice and snow.

Baby, it’s cold outside. Console your green thumb by tackling some February garden projects.

Veggie Planning

Grab a sketch pad or some graph paper and plan your vegetable and flower beds. You can work out crop rotation, placement and successive crops without getting your hands dirty.

Beginning gardeners – and those that want a refresher – might appreciate this reference from our Seed to Supper webpages that take you from seed to harvest (hence the name!) Guides are also available in Spanish! ¡Las guías también están disponibles en español!

Weeding

Okay, if you want to get your hands a little dirty, pull a few weeds. Winter weeds pop up here and there and many can be vanquished with a quick dig or tug in our soggy soil.

Here’s a nice reference for weed ID and management:

Groundsel is a winter weed that can be identified from its frilly leaves that are dark green to purple and yellow flowers that quickly go to seed. — Common groundsel is a winter annual weed you can manage now by pulling or digging.
Photo credit: Betty Marose

Garden Bones

While you’re scouting for weeds, look at your garden’s basic structure – its bones. Without the distraction of leaves, it’s easier to identify areas that could use an arbor, trellis or hardscaping.

You’ll probably spy opportunities to liven up your winter landscape, too. How about a sweep of native grasses, a winterberry pop of red, or bright yellow and oh-so-fragrant wintersweet?

Carry a notepad to capture all your ideas. Wouldn’t a big container make a marvelous focal point there? And that downspout is crying out for a rain barrel, isn’t it?

a winterberry shrub full of red berries — Winterberry Holly (*Ilex verticillata*).
Photo: Stacy Small-Lorenz, UMD Extension

Pruning

January to mid-March is prime time for pruning most trees and shrubs. Make sharp cuts at an angle. Remove no more than a third of the plant. And step back often to avoid overdoing it. Here’s a good pruning guide.

February also marks the season for grapevine pruning. My collection of grapevine wreaths from trimmings ranges from petite 3-inch rings to 2-foot whoppers.

Starting Seeds

Get a jump on spring by starting some plants from seed under grow lights. Now is a good time to start peppers, onions, broccoli, cabbage, cauliflower and Brussels sprouts.

Growing plants from seeds gives you more choices for plant varieties, organic growing options, and the satisfaction of growing your own food from start to finish. Plus, you can save money. Learn how on our Staring Seeds Indoors page.

I enjoy the glow of a friend’s grow lights as I drive by her home each winter. I can see the tidy rows of sprouts in my mind regardless of the amount of ice and snow piled around me.

Seedlings emerging from soil. — Starting seeds indoors jump-starts your growing season.
Photo credit: Home & Garden Information Center

Ice and Snow Damage

Deal with that ice and snow gently. To remove snow from tree branches without damage, brush up, not down. If ice coats the branches, let it melt naturally.

Should winter’s worst snap off a branch of a tree, make a clean cut now or in early spring. Clean cuts heal faster. Call on an arborist for jobs too big to tackle on your own.

Broken branch on a tree in winter. — Make a clean cut on winter-damaged branches to minimize health impacts.
Photo credit: Home & Garden Information Center

Feeding Birds

Wintertime can be a tough time for birds, too. To ensure their springtime birdsong and bug-eating services, keep their feeders clean and well-stocked.

Tool Maintenance

Are you looking sharp? How about your tools? If you didn’t sharpen your garden tools in the fall, do it now to have them ready for spring. Here’s a reference that includes tool care tips.

See? I told you there were a dozen different ways to keep your green thumb happy this winter. Grab some graph paper, seed catalogs, notepad and pruners and get going!

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. Read more by Annette.

Gardeners Wrap Up the Gardening Season

November 22, 2024November 18, 2024Maryland Grows1 Comment

Okay, gardeners. We can see the finish line. It’s been a busy gardening season, but we are almost ready to wrap things up for the year. Almost.

October and November are the wrap it up, clean it up months. Now’s the time to give the last of your withering vegetable plants the heave-ho.

I know there is still one tomato out there, but it’s a brick. Let it go. Toss healthy plants on the compost pile and bag and trash the rest.

Are you one of those garden daredevils who cheat the season with late plantings of cool weather crops? Good for you. Just be ready with frost protection such as floating row covers or a deep layer of straw.

vegetable plant with a row cover — Floating row covers extend the growing season. Photo: UME/HGIC

Cut back any perennials that had serious disease or insect problems, but leave the rest standing to provide food and shelter for birds and overwintering pollinators and beneficial insects.

Mums have sensitive crowns – the part where the roots and stems meet– so treat them gently. After their fall show, leave them standing to increase their chances of coming back. Not all hardy mums are hardy.

Use leaves as mulch around trees and shrubs and in your vegetable and flower beds. Use a fine layer on your lawn and toss the rest in your compost pile.

Collect fallen branches to start a brush pile for wildlife. Put larger pieces on the bottom and smaller ones on the top to create cover and resting places for creatures great and small.

Yes, you can still sneak in some bulbs. Remember to plant them three times as deep as they are wide. In other words, a 1-inch daffodil bulb goes into a 3-inch hole.

You can plant trees and shrubs until the ground is frozen, too. Earlier is better to give roots a chance to get established. Just make sure you water them deeply every week.

red leaves on a tree — There’s still time to plant trees such as this native black gum *(Nyssa sylvatica)* with brilliant fall color. Photo: T. David Sydnor, Bugwood

Here’s a fact sheet that tells you how to plant trees and shrubs and lists plants that are best planted in the spring.

Also deep water any tree or shrub you planted earlier this year to send them into the winter well-hydrated. Water until we get a ground-penetrating frost, usually around Thanksgiving.

Water any newly planted trees and shrubs to help them overwinter. Photo: M. Talabac, UME

Want a live Christmas tree? Save yourself some colorful language by digging the planting hole now before the ground freezes. Drop in a few unopened bags of mulch to avoid losing Bowser or any holiday guests in there.

We’re almost to the cuddle up with cocoa season. Taking care of these few last-minute garden tasks will let us smile and sigh under the afghan, reveling in a job well done.

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension.

This article was previously published by Herald-Mail Media. Read more by Annette.

Q&A: What is a Good Substitute for Spruce?

September 18, 2024September 17, 2024Maryland Grows2 Comments

blue atlas cedars in front of a building — Blue Atlas Cedars on the American University campus in Washington, D.C.
Photo: M. Talabac

Q: I have always loved the look of blue spruces, and I see many Maryland nurseries stocking them. I’ve heard that I should consider alternatives, though. Why?

A: Although every plant has something it can be vulnerable to (pests, diseases, environmental stress) and nothing is risk-free, Colorado spruce (Picea pungens), the species with the popular blue-needled cultivars, struggles in Maryland growing conditions. As such, it is at risk for several problems that cause dieback and significant aesthetic damage. Overall, spruces as a group are not well-adapted to high summer heat and humidity, or compacted or clay-dominated soils common to urban or suburban landscaping.

No spruces are native to the state except for the tip of western Maryland, where the locally rare red spruce grows in the mountains. (Maryland Biodiversity Project notes that prior logging and wildfires reduced this already limited population.) You can see from the spruce species range maps on the Biota of North America Program website that no other spruce species grows wild anywhere near Maryland.

Due to the particularly damaging nature of the issues spruces can develop here, primarily from fungal infections — drastic needle browning and shedding, plus branch dieback — I suggest using alternatives if you want a large-statured, pyramidal, and/or blue-leaved evergreen specimen tree. This spruce decline issue is prevalent enough that it has its own University of Maryland Extension web page, “What’s Wrong with my Colorado Blue Spruce Tree?”

A substitute plant won’t necessarily look the same (it might have broader or looser branching, or won’t have blue foliage), but it can have a better chance of thriving. Your options will depend on the site conditions, including how much space you have for the plant to mature, though your best range of choices will be for a location in full sun (in summer) with good drainage and no deer browsing pressures.

Few locally native species are evergreen and large-statured, but they include American holly (Ilex opaca), Eastern redcedar (Juniperus virginiana), and Atlantic whitecedar (Chamaecyparis thyoides), the latter of which is rare, unfortunately hard to find for purchase, and limited to the coastal plain in the wild. Several species of pine grow wild throughout Maryland, but their mature habit is quite different from spruce.

Eastern redcedar tree — *Left: Eastern redcedar (Juniperus virginiana), Right: American holly (Ilex opaca). Photos: M. Talabac*

American holly tree — *Left: Eastern redcedar (Juniperus virginiana), Right: American holly (Ilex opaca). Photos: M. Talabac*

Non-native candidates include other holly species or hybrids, Japanese cedar (Cryptomeria japonica), true cedars (Atlas Cedar, Cedrus atlantica, and Deodar cedar, Cedrus deodara), and Western arborvitae (Thuja plicata). Arizona cypress (Cupressus glabra) and atlas cedar come in silvery-blue forms if you want a foliage color similar to blue spruce. While leyland cypress (Cupressocyparis leylandii) is commonly planted, it suffers from some serious shortcomings that can make it short-lived and prone to fungal branch dieback.

Arizona cypress tree — *Smooth Arizona cypress (Cupressus arizonica glabra). Photo: M. Talabac*

Whichever plants you try, use a mix of species if you’re growing them in a group, like a screen or living fence, rather than mass-planting only one species or variety. This helps the planting to resist future pest, disease, or weather stress problems, since different species have different tolerances and vulnerabilities. That way, a future issue won’t be likely to impact them all equally severely, like a fungal needle cast infection wiping-out a row of blue spruce.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. Read more by Miri.

Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension. Our horticulturists are available to answer your questions online, year-round.

Q&A: Reduce the Height of an Arborvitae?

July 16, 2024July 16, 2024Maryland GrowsLeave a comment

Arborvitae (*Thuja* sp.). Photo: Jason Sharman, Vitalitree, Bugwood.org

Q: I need to reduce the height of an arborvitae…. I might take around 5 feet off the top because it’s too big. When should I prune?

A: While late winter or early spring is generally a good time to prune conifers (needled evergreens), in this case timing won’t matter much, because the amount you want to remove is more than the plant can handle. Instead, it may be better to replace the plant with a smaller-growing option.

Most conifers, including arborvitae, do not regrow foliage when it’s lost due to heavy pruning, deer browsing, or crowding from being planted too close together or too close to a wall or fence. Unlike broadleaf evergreens (boxwood, holly, euonymus, etc.), they don’t have dormant buds along the older stems, lying in wait to grow if the branch or foliage beyond them is removed.

Once the foliage is gone and bare wood is visible, it’s not coming back on that part of the plant. This is the reason why deer-browsed arborvitae are easy to spot, developing a shape sort of like a stemmed flute glass, because the parts the deer can reach become stripped of foliage and never fill back in again, even as the out-of-reach tops get wider.

As conifers age, it’s perfectly normal for the innermost branches to become quite bare, as those older leaves shed over time. They are deliberately jettisoned by the plant because they are being progressively shaded by the outer shell of live growth, so they cost the plant more to keep alive than the meager photosynthesis energy they get back. This will be exacerbated if the plant is sheared, where the foliage tips are lightly trimmed to give the plant a more manicured look, because that makes the layer of foliage casting shade on the plant’s interior even denser.

Pruning cuts that take off that outer layer or shell of younger growth on the branch tips will result in permanent bare areas. Once the foliage is gone from that inner wood, it will not regrow, even if sunlight now reaches the interior due to pruning cuts. This also applies to the main leaders. Reducing the height of a tall arborvitae will stunt the top growth and give it a permanent gap or flat-looking top. If this isn’t really visible from where you typically view the plant, then it’s not necessarily a problem (assuming the pruning cuts seal-over well and don’t develop wood decay). Otherwise, nothing will give the plant its former shape back.

Fortunately, there are lots of compact and dwarf conifer varieties on the market these days. A couple conifer types, like yews, will be able to rejuvenate after heavy pruning. Even so, it’s still best practice to select a plant that should fit in a given space in the yard without relying on pruning to make it fit.

I acknowledge that there are many gardeners that inherit poorly-chosen plants in their new yards, but if or when it comes time to replace them, research your options to make sure you won’t run into the same problem down the road. Plants never really stop growing, though older specimens can slow down. Due to a reduced growth rate, dwarf and miniature cultivars will stay much smaller over the same amount of time as their full-size counterparts, even though some dwarf cultivars can also get larger than you’d expect a few decades after planting.

Lilac Rejuvenation by Pruning

June 26, 2024June 25, 2024Maryland Grows2 Comments

Each year, the spring and summer seasons seem to go faster and faster, and 2024 is no exception. If you have a lilac shrub, you can probably still imagine the sweet fragrance and beautiful flowers from a few months ago. I get several questions each year about lilacs, so the blog today is going to answer some of those inquiries!

A few years ago, we decided to begin excavating for our new garage in late summer, and unfortunately, had to move a lilac shrub. The transplanting was not as high of a priority as it should have been, and the shrub suffered tremendously the following year. We gave it a season to see if it would recover, but ultimately, it was too damaged. At that point, we decided to try rejuvenation pruning and cut everything back to 6” above the soil line in hopes that the shrub would come back and have a better overall shape and appearance. We had nothing to lose as the plant was suffering, not growing, and not flowering.

*A lilac that was transplanted at the wrong time of the year and damaged. Photo: A. Bodkins, UME*

Question: What is rejuvenation pruning?

Answer: Lilac rejuvenation pruning involves cutting the entire woody shrub back to a few inches above the soil surface. This can be done if a shrub is really scraggly or if you want to change its shape entirely. Last summer, my parents had to do a construction project behind their very large, 20+-year-old white lilac, and they had to cut it back to the ground. It seems to be rebounding just fine, though!

University of Nebraska-Lincoln Extension guidance recommends doing rejuvenation pruning in late winter or very early in the spring.

*March 8th: First sign of life on the rejuvenation pruning. Photo: A. Bodkins, UME*

a lilac bush that was pruned severely now has new green leaves — *June 4th: Regrowth progress. Photo: A. Bodkins, UME*

Question: My lilac has not bloomed for the last several years. What could be wrong? It used to be beautiful each spring!

Answer: Lilacs need full sun to bloom. Often in people’s landscapes, as trees mature, lilacs get less sun than they once did, leading shrubs that once produced abundant, full blooms to have limited to no blooms.

Question: Why did my lilac bloom in the fall?

Answer: Environmental stress can cause out of season blooming. Some examples include drought, excessive heat, defoliation from pests, heavy pruning, insects, or diseases.

Question: What time of year should I prune my lilac?

Answer: Many spring-blooming, woody shrubs will set the flower buds for the next season’s growth in late spring or early summer, so be sure to prune for shaping and maintenance purposes as soon as the shrub is finished blooming for the current growing season.

For more information on lilacs, see the Home and Garden Information Center’s page, Lilac: Identify and Manage Problems — particularly the sections on diseases, insect pests, and heat-tolerant and powdery mildew-resistant varieties.

Remember, you can always contact your local University of Maryland Extension office or use Ask Extension to get answers to all your gardening questions.

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland. Read more posts by Ashley.

Q&A: What Screening Plants Fit in a Small Space?

March 18, 2024March 14, 2024Maryland Grows1 Comment

a row of small evergreen arborvitae shrubs near a brick building — ‘Emerald Green’ Arborvitae screening a property line. Photo: Miri Talabac, University of Maryland Extension

Q: I have limited space in a tiny city front yard and would like to block some of my view of the street. What types of evergreens would work well but not get too wide?

A: The width of the mature plants is the tricky part, since many upright evergreens mature at least 3 to 5 feet wide at their base, and not many are trimmable to keep them smaller. Plant options will depend on whether you have full sun or some shade from nearby trees or the house itself. Few city yards have issues with deer (though some do), so I’ll assume for now that browsing is not a factor.

Soil compaction is a common challenge, and poor drainage (is a roof downspout nearby?) can exacerbate root stress and cause plants to fail. If the site drains reasonably well and receives full sun in summer, your choices include slender-growing cultivars of widely-used evergreens. (Alas, there are very few native options to fit these criteria.) Examples include arborvitae (Thuja), juniper (Juniperus), yew (Taxus), Japanese plum yew (Cephalotaxus), boxwood (Buxus), and holly (Ilex).

Yew as well as broadleaf evergreens like the boxwood and holly can be pruned relatively easily to manage size, since they rebound well. Even so, it’s best to select cultivars that will mature close to the size you can accommodate without having to prune, both to save yourself the task and to reduce plant stress.

For the rest of those listed plants, especially other conifers (needled evergreens), pay close attention to expected mature size on the plant tag and make sure you have room, taking into account overhead utility lines. Take that stated size with a grain of salt too, since older plants keep growing and will not plateau at a set height forever.

Yew, Japanese plum yew, boxwood, and holly will handle a fair amount of shade and still look good, though the less sun they get, the less dense they might stay (or growth will slow). None of these species are super fast-growing (otherwise they’d get much too large for the space), but boxwoods and the upright yew varieties are among the slowest in pace. Even so, planting small, young specimens will be easier on both you and the plants (especially if shade tree roots are infiltrating the area), and they will catch up.