Pansies Out/New Plants In

If you filled your containers with pansies early this spring, they have provided lots of color but are starting to get a bit long in the tooth. It is time to pull the pansies out and plant containers for summer show.

Soils for containers must be well aerated and well drained while still being able to retain enough moisture for plant growth.  Don’t use garden soil in your containers, it is too heavy and won’t drain properly.  Purchase a soilless mix designed for use in containers.  For succulents, herbs and perennials, select a coarse soilless mix with more bark, perlite or sand because these plants need good drainage and you don’t want the mix to retain moisture over long periods of time.  For tropical and foliage plants, choose a media with more peat and less coarse material as these plants tend to prefer moister growing conditions.  Moisten your media slightly before planting by filling a tub with media, adding water and mixing.  Remember, containers must have a drainage hole.

Think of your container garden as a living flower (and foliage) arrangement.  Include a tall plant in the center or back of the container.  Select filler plants to provide interest and use cascading plants to soften the edges.  Consider plant requirements when planning combination containers.  Use all shade plants for shady locations and sun-loving plants on a sunny patio.  If you use a combination of sun-loving and shade-loving plants in a single container, there will be no appropriate exposure for the container.  Also, think about moisture requirements.  Don’t combine plants that like it moist with plants that require good drainage.  You can combine shrubs, perennials and annuals, but the annuals will need to be replaced the following year.  Depending on the size of the container and exposure, the shrubs and perennials may overwinter in the container.  Tropicals are fun to add in a combination container, but you will need to bring them indoors to survive the winter.  If you combine a shrub and a tropical, you will have a conundrum—bring it in and the shrub will suffer; leave it outdoors and the tropical will die.

Ornamental sweet potato vine (Ipomoea butatas) is a great annual to use for summer containers.  You can get chartreuse and black varieties that make a bold statement with flowering plants.  They are spillers, that soften the edge of the container. Another good chartreuse plant for container gardens is hakone grass (Hakonechloa macra). Its arching, mounding habit will flow over the edge of the container.  Euphorbia Diamond Frost (Euophorbia hypericifolia ‘Inneuphe’) is a great plant with a small white flower that blooms in profusion from spring to frost.  It is a great filler in a container planting.  Another good filler is sweet alyssum (Lobularia maritima). I planted some in a container near my carport and every time I get out of my car, I notice the sweet smell. Coleus comes is so many wonderful foliage colors these days and will do a great job of filling out a container.

For the tall statement plant in your container, consider papyrus (Cyperus papyrus) if you can keep it moist. Another moisture loving plant for the background is soft rush (Juncus effusus). For a dry container, use an ornamental grass like purple fountain grass (Pennisetum setaceum) or Mexican feather grass (Nassella tenuissima).  You can even use the” impossible to kill” snake plant (Sansevieria laurentii) or ti plant (Cordyline fruticosa), both common houseplants.

Dusty miller (Jacobaea maritima) comes in different leaf forms and adds an eye-catching silver to the mix.  All these plant suggestions and I haven’t even touched on flowers!  Go to your local garden center and chose the flowers you like in the colors that match your outdoor décor.

Once you have selected your container, growing media and plants, fill the container (almost full) with media.  Arrange the plants on the surface and play with the design until you are happy with the combination.  Remove each plant from its plastic pot and loosen the roots, especially if they are circling within the container in which it was grown.  Add a bit more media and water thoroughly.  Watering after planting settles the media and eliminates air pockets.  You may need to water several times to insure the media is thoroughly moist.  Make sure water drains out of the hole in the bottom of the pot.  A waterlogged container will not thrive unless you are growing water plants.  Remember to water container plants frequently throughout the summer.  Soilless media dries out more quickly than garden soil.  Fertilize containers a few times during the summer.  Annuals and tropical will need more frequent fertilization than shrubs and perennials.

Simple container showing off the beauty of coleus.

Nice color palette in a container grouping at Longwood.

Papyrus in containers at Chanticleer.

Spring has Sprung

One of the things I love about spring are the fleeting perennials that bloom in early to mid-spring and then disappear–the spring ephemerals.  An ephemeral is a plant marked by a short life cycle.  Desert ephemerals take advantage of short wet periods in arid climates.  Mud-flat ephemerals grow in short periods of low water in human disturbed habitats.  Spring ephemerals are perennial woodland plants that grow in early spring, quickly bloom and produce seed.  As the temperature warms into late spring and summer, the foliage yellows and dies back leaving only underground structures (roots, rhizomes, bulbs) for the remainder of the year.  Then, next spring the cycle repeats itself.  These small herbaceous plants take advantage of sunlight reaching the forest floor that will be blocked as soon as forest trees leaf out fully.

One of the first spring ephemerals to bloom is the skunk cabbage (Symplorcarpus foetidus).  Skunk cabbage, you say?  I didn’t know skunk cabbage had a flower.  These flowers are subtle, blend in with the forest duff, and bloom extremely early (February-March) before most people have thought about entering the woods.  If we get a warm late winter day, in can be fun to go looking for the skunk cabbage flowers.  Find a moist woodland and look carefully.  Now, though, is the time skunk cabbage really shines.  The huge, almost chartreuse leaves brighten up the forest and make big sweeps in wet areas.  They do go through an awkward period as the foliage dies back, but don’t we all at one time or another.

My favorite spring ephemeral story is one I tell on myself. When I moved into my current property and was the proud owner of a bit of piedmont woods, I wanted to plant native plants and help the forest along to be all that it could be.  At the University of Delaware Botanic Garden Plant Sale (April 27 this year at the College of Agriculture and Natural Resources in Newark) I bought a flat of trout lilies to plant in the woods.  Trout lily (Erythronium americanum) has a small yellow flower with recurved petals.  It gets its name for the small mottled leaves that look like the skin of a brook trout. That afternoon, I proudly trudged down into the woods with my flat of a dozen trout lilies to find hundreds (maybe thousands) of them blooming in the stream valley.  It seemed ridiculous to add my freshly purchased twelve to nature’s bounty already thriving.  I could have planted them closer to the house in a landscape bed, but I didn’t have the moist conditions they need to thrive in a bed, so I took the plants back and let someone else find a good home for them.

Another favorite spring ephemeral is Virginia bluebells (Mertensia virginica). Virginia bluebells also grow in colonies in stream valleys, but you can plant them in moist garden beds. Soft magenta buds open to tubular sky-blue flowers.  They last a few weeks but are so cheery while in bloom they are worth the short appearance.

Bloodroot (Sanguinaria candensis) is a great spring ephemeral because the foliage is interesting after the flower is gone. Flowers have 8-12 delicate white petals surrounding bright yellow stamens.  Each flower is borne on an individual stalk before the leaves unfold. Once the flowers die back, you can easily spot the distinctive large basal leaf with five to seven lobes.  Bloodroot seeds are spread by ants. The seeds have a fleshy organ, called an elaiosome, that attracts ants.  The ants take the seeds back to their nest, where they eat the elaiosome and the seeds fall into the nest debris, ready to germinate next year.

One of the biggest threats to spring ephemerals in the mid-Atlantic woodland is an invasive plant called lesser celandine (Ranunculus ficaria). It is also a spring ephemeral but comes from Eurasia.  It emerges earlier than our native spring ephemerals and is so vigorous it forms a dense carpet in the woods, shielding our native plants from the sunlight and competing for resources.  Some of the invasive plants in our woodlands confuse native insects.  Garlic mustard (Alliaria petiolata) looks a lot like our native cut-leaf toothwort (Cardamine concatenata).  So much so that West Virginia white butterflies, whose only food source is native toothwort, mistakenly lay their eggs on garlic mustard.  When young larvae emerge, they feed on garlic mustard leaves and most die.

One of the best places to see spring ephemerals is Mt. Cuba Center in Hockessin, DE.  Their Annual Wildflower Celebration is Sunday, April 28.  If you go you can enjoy a magnificent display of spring ephemerals at their annual celebration of the season. Stroll through the native plant gardens at the peak of their glory; enjoy live music, gardening demonstrations, family programming, and more. A variety of food selections are available and, in response to requests from Mt. Cuba Center’s visitors, a selection of native plants will be available for purchase, while supplies last.  If you miss the Wildflower Celebration, you can still visit Wednesday to Sunday from 10 AM to 4 PM (April through November), but hurry before the ephemerals disappear.

If you want to purchase native plants for your woods or anywhere is in your garden, try the UDBG Plant Sale at Ag Day on Saturday, April 27, Delaware Nature Societies’ Native Plant Sale at Coverdale Farm Preserve on May 3 and 4 and Brandywine Conservancy on May 11 and 12.  Of course many local garden centers also carry native plants.

Skunk cabbage flowers peaking out from a patch of moss. Photo credit: Sue Barton

Virginia bluebells in a Landenberg garden. Photo credit: Rick Darke

Close up of Virginia bluebells. Photo credit: Rick Darke

Stop Those Invasives!

We are on the brink of Callery pear bloom in early April. Our roadsides and abandoned fields will soon explode into a sea of white blossoms.  This may look “pretty”, but if you understand ecology and the impact these aggressive trees have on our ecosystem, you are more likely to feel anger than see attractiveness. Pyrus calleryana ‘Bradford’, the first Callery pear cultivar, has a weak branch structure with V-shaped branch angles that split after 15 to 20 years of growth. Narrow branch angles prompted the breeding and release of many more cultivars such as ‘Cleveland Select’, ’Chanticleer’ and ‘Aristocrat’. In the past, Bradford pear was almost sterile and produced only a few fruits, but with so many newer cultivars in the landscape, they can now cross pollinate and produce an abundance of fruit. Fruit are small and inedible but are carried by birds who drop seed in roadside ditches, easements and natural areas.  Many of these invasive flowering pears have thorns and aggressively choke out native trees, like serviceberry that once bloomed along wood edges in early spring. Do not plant Callery pears and consider removing and replacing any growing on your property with a native small flowering tree, such as dogwood, fringe tree, serviceberry, or redbud.

Japanese stilt grass (Microstegium vimineum) is another problem plant in our region.  It is an annual grass that has become the default groundcover for roadsides, much of our wood edges and even established woodlands.  It thrives in shady sites but will also grow in the sun.  Japanese stilt grass germinates in the spring, about two weeks before crabgrass, but doesn’t flower and produce seed until early fall.  It is a sprawling grass that roots at the nodes and can completely cover other low growing plants. Our first opportunity for control is to treat known areas of stilt grass with a preemergent herbicide, much like we control crabgrass.  The difference is that when we control stilt grass, the herbicide should be applied two weeks earlier than for crabgrass control.  You can also control Japanese stilt grass by mowing it in September as it starts to flower but before seeds ripen.  You can prevent a new crop of seeds from developing and growing the following year.  The trouble with this strategy is there is so much stilt grass seed around that seed can easily blow into an area you have mowed.   Stilt grass is easy to pull, so it can be removed from landscape beds, but that strategy isn’t practical for the lawn or large areas of roadsides or woodlands.  Work has begun on biological control (Japanese stilt grass is kept in check with insect pests in its native regions) but beneficial insect release is many years away.

These are just two examples of invasive plants that are changing the environment in which we live.  Think long and hard before planting a known invasive plant in your landscape and consider removing the ones you already have.  For a list of plants on the Delaware Invasive Species List, visit

Invasive pears along Delaware’s roadside.

Close up of Japanese stilt grass flowering in the fall.

Plan for Planting

Early March is time to start planning for the spring planting season, the perfect time to rethink your landscape.  I recently read a blog about a great concept.  The blog author, Jim Anderson, credits native plant speaker, Gerould Wilhelm, with a simple synopsis—plants live in communities in the wild and should also in urban and suburban plantings.  This is not the first time I’ve heard this recommendation.  Years ago, Paula Shrewsbury from the University of Maryland did some research on why azaleas get bad lacebug infestations if they are in sunny locations.  Since azaleas prefer a partially shaded site, she supposed azaleas in a sunny location might be stressed and send out an attraction signal to lacebugs making the azaleas more susceptible to attack.  Her research did not support that hypothesis, but it showed something else. Azaleas growing in the shade are part of a complex community that supports more insects, some of which are lacebug predators.  So, it is the complexity of the landscape in the shade that provides biological control of lacebugs resulting in less damage to the azaleas.

In a complex community, like a forest or a multi-level landscape bed (ground layer, shrub layer, understory tree and canopy tree layers), some roots die every year.  Those dead roots provide organic matter to improve soil structure and provide channels in the soil for needed air and water to flow to plant roots.  If you were a tree, would you rather live as a part of a community with other plants where you get watered and feed by the plants around you or would you rather live in a ring of wood mulch and a shallow-rooted lawn that often forms a barrier to rain and air exchange.  Easy choice, right?

In Gerould’s talk he goes on to describe a project at a school in which a first-grade class plants a native tree in a large circle (3-4-foot diameter).  The grass is removed, and native plants associated with that tree are planted.  If the kids planted a bur oak (Quercus macrocarpa) they could surround it with associated native plants like wild geranium (Geranium maculatum), Jacob’s ladder (Polemonium reptans) and Pennsylvania sedge (Carex pensylvanica).  Each year, the class (now second graders) can expand the circle and plant more native plants.  Eventually, by about fourth grade, the circle would be big enough to accommodate shrubs or small trees.  Imagine a school yard in which each class of first graders progressing through the school was working on its own “tree circle.” By eighth grade, the students would understand the concept of community.

I saw the concept of community in a vivid example last summer when I was biking with a friend in Newark.  There is a street where narrow backyards back up to the road.  Each homeowner treats their backyard differently, but because they are all lined up, they are easy to compare.  To some people, the perfect aesthetic is a clean, neat mowed lawn from the back of their house to the street.  Others though, opt for a complex community growing in their backyard.  Everyone has the right to their preference and to treat their backyard as they wish.  But, when more people chose the community concept, our suburban landscape does a better job of providing the ecosystem services we need to survive.  It also results in “happier”, healthier plants.

Suburban back yard with neat mowed back yard.

Suburban back yard with complex community of trees, shrubs and ground cover.

Delaware Plants of 2019

Every year the Delaware Nursery and Landscape Association selects an herbaceous plant (usually a perennial that dies back to the ground each winter) and a woody plant (usually a tree or a shrub) to designate as Plants of the Year.  Plants are selected that will thrive in Delaware’s conditions and that have few disease and insect problems.  If sited properly, these plants are guaranteed to succeed.  These plants are often underused in the Delaware landscape.  So, if you purchase one of these plants, you will be a trendsetter in your neighborhood.  The 2019 selections were just announced at the Delaware Horticulture Industry Expo in Dover.

Common Ninebark – Physocarpus opulifolius

Common ninebark is an excellent native shrub for year-round interest. White flowers appear in dense, spirea-like clusters in spring, and give way to clusters of reddish-pink capsules. The clusters eventually turn brown and persist into the winter. The leaves are yellow in the fall. Named for its unusual bark which peels in strips to reveal several layers of reddish to light brown inner bark, ninebark is a popular ‘winter interest’ shrub. Arching branches give this shrub as mounded habit and in groups it makes an excellent hedge and provides good erosion control. Bees are frequent pollinators of ninebark. Ninebark grows in full sun to partial shade and has few disease or insect problems.  It can be cut back to the ground in late fall for complete rejuvenation.

Golden Ragwort – Packera aurea

Packera aurea has the unfortunate common name of golden ragwort.  It is none-the-less a vigorous and useful native perennial that thrives in moist shady (or sunny) locations, naturalizes rapidly and produces a long and profuse spring bloom. Flat-topped clusters (corymbs) of yellow, daisy-like flowers create blankets of yellow in the early spring landscape. Once it flowers, it is best to cut off the spent flower heads, so you can enjoy the dense groundcover of heart-shaped, toothed, dark green leaves that often have a purplish tinge beneath. Synonymous with and still frequently sold as Senecio aureus.

Visit a garden center in Delaware this spring and pick up one or more of these great plants for your garden!

Golden ragwort makes a carpet of yellow in the spring landscape.

Pruning 101

Now that the leaves have fallen, it is time to pick up your pruning shears, loppers and pruning saws.  The best time to prune trees and shrubs is when they are dormant.  You can easily see branches to determine which to prune and plants have stored food in their roots, stems and branches so they will not re-sprout from pruning cuts now.  Prune trees when they are young for several years to establish an appropriate shape and you won’t need to continue pruning as they age. Pruning is truly and art and a science.  Prune to shape trees and shrubs to grow in their natural habit, but also prune properly to avoid spreading decay throughout the plant.

There are two important pieces of information to remember about the way trees grow.  First, branch tissue and trunk tissue are separate.  Second, trees never heal, but then can compartmentalize and seal wounds.  They seal wounds by growing callus tissue around the cut.  Decay spreads most easily vertically in a tree, so it is critical to cut only branch tissue and not allow decay to enter the trunk. When cutting a branch, always prune outside the branch collar (swollen area at the base of a branch).  Never cut flush with the trunk as you will be cutting into trunk tissue and opening the tree for spreading decay.   Forget about using a wound dressing, they only inhibit the tree’s natural callus response to a pruned branch.

Start by pruning any dead, dying or diseased branches.  These branches can be pruned at any time of year.  Next, look for rubbing or crossing branches.  Rubbing branches may create a wound that will be open for insect and fungal entry.  Crossing branches can eventually become rubbing branches as they grow.  Remove branches that are growing back into the center of the tree and keep branches growing outward.  Finally, remove water sprouts and root suckers.

Use the appropriate tool for the job.  Pruning shears are handy but shouldn’t be used on branches larger than ½ inch in diameter.  Lopping shears give you more leverage and can prune slightly larger branches.  For branches greater than ¾ – 1 inch, switch to a pruning saw. Pole pruners can be used to prune branches that are too high to reach but be careful of overhead wires when using pole pruners.

If branches are large, use three pruning cuts to prevent the weight of the branch from peeling back bark and allowing the wound to enter trunk tissue.  Start by undercutting the branch about 4-5 inches away from the trunk.  Then saw through the entire branch outside that undercut, removing most of the weight of the branch.  Make your final cut just outside the branch collar.

Hedge clippers should only be used for pruning shrubs maintained as a formal hedge.  Always prune the top narrower than the base to light reaches all the branches of the hedge.  There is no shrub that should be pruned into a ball, despite what you see in the landscape around you!  Prune individual shrub branches just above a node or bud to reduce the size and maintain natural shape.

Some shrubs respond well to rejuvenation pruning.  Redtwig dogwood, for example, can be cut back to 4-6 inches above the ground and allowed to regrow new branches that will be vigorous and more brightly colored.  When you want to encourage new growth, prune late in the winter just before growth starts.  If your goal is to reduce plant size, prune in the summer when most of the plant’s resources are depleted.  For blooming shrubs, prune after the shrub flowers.  Some shrubs bloom on new wood and will respond well to a dramatic pruning.  Other shrubs bloom on old wood and removing too many branches will dramatically reduce flowering.

Red twig dogwood responds well to rejuvenation pruning and will grow bright red new twigs for the following winter.

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