Gardens are Great!

In this crazy time of limited travel and socializing, one thing we can engage with fully is our garden.  This pandemic has brought out the ultimate in cocooning to the benefit of many home landscapes.  More time on your hand? More opportunity to spread mulch, weed and prune.

When spreading mulch, be sure to use an organic mulch that will decompose, adding nutrients and improving the structure of your soil. My preference is leaf mulch, but bark mulch or well composted yard waste is OK, too.  Avoid dyed mulches. The dyes can be toxic to plants and dyed mulches are usually made from un-composted wood high in carbon that can pull nitrogen from the soil as it decomposes.  Plus, mulch dyed red is just unnatural looking and has no place in a landscape.  Also, be careful to rake old mulch before adding new mulch to prevent a hydrophobic crust that prevents water from reaching the soil and ultimately plant roots.  Add only a small layer of new mulch to your garden beds.  Mulch should be no thicker than 2-3 inches including both new and old mulch layers.  Do not pile mulch up around the base of tree, despite what you see in public landscapes or neighbors’ homes.  Mulch mounds are a ploy by unskilled landscapers to make you buy more mulch. Mulch mounds promote a moist environment around tree trunks and cause decay, allowing the entry of insects and disease organisms.  Some people think they are preventing weeds by piling on the mulch, but a thin layer will prevent most annual weeds from germinating and perennial weeds, like dandelions, can grow though any thickness of mulch.

Most pruning should be accomplished in late winter and early spring before trees and shrubs leaf out.  But some shrubs that bloom on old wood are better pruned right after flowering.  Also, some plants will have dieback and it is hard to see which branches require pruning until the tree or shrub has leafed out fully.  Now is the time to carefully prune dead branches back to the nearest live branch.  That can be tedious work, but your trees and shrubs will look much better when cleared of the dead branches.

Weeding can be an undesirable task or an absolute pleasure depending on your frame of mind.  If you have a comfortable pad for your knees, a good weeding tool (like a narrow trowel or a hori hori), a pair of well-fitting garden gloves and a bucket for placing your weeds, I can think of nothing more satisfying than making your way from bed to bed and pulling weeds in your garden. Be sure to pull out the entire plant, including the roots.  If you pull the top of the weed, you have only solved the problem temporarily.  Some plants may even grow back more vigorously when their foliage is removed.

The long, cool spring has been great for many plants.  Blossoms on spring blooming trees (other than saucer magnolia that got hit by our late frosts) have lasted much longer than normal.  Now that we are getting some warm days, you can start putting foliage plants outdoors and pot up containers of annuals and mixed tropicals. Take some time to walk around your garden and notice the subtle changes that occur daily as well as the “wow” aspects of your garden that are unmissable (like this sweep of golden ragwort – Packera aurea).

The bright yellow sweep of golden ragwort (Packera aurea) is much prettier than its name.

Lessons from Brazil

In January, I led a study abroad to Brazil for UD with my colleague, Anna Wik—what an experience!  We took 14 students to the Amazon region and stayed in floating lodges to learn about the flooded rainforest ecosystem (Varzea). The water rises 12 meters during the rainy season and animals must find refuge in the trees (including the elusive jaguar).  After the Amazon, we traveled to Rio de Janeiro, where we studied the work of Roberto Burle Marx.  This famous landscape architect died in 1994, but not before leaving a legacy in Brazil and throughout the world.  What can we learn from him today?  Lots! He is credited with being the first landscape architect to celebrate the native plants of his homeland.  When he started designing landscapes in Brazil, most landscapes were comprised of European plants, but Burle Marx loved the bold textures of native tropical flora and used them in his designed landscapes.  The benefits of using native plants in planned landscapes are well-known now but not always practiced.

Roberto Burle Marx approached landscape design as a painter and used the landscape as his canvas.  The renovated Cavanella’s landscape just north of Petropolis is a fantastic example of the brush strokes he painted with plants.

Cavanella’s gardens designed by Roberto Burle Marx with a home designed by Oscar Niemeyer taken on a recent visit by a UD study abroad.

Burle Marx had a passion for plants and discovered many new species and cultivars, some of which bear his name.  In his sitio (ranch) about one hour outside Rio, he displays many of those plants, but his gardens also include built features in which he reused recycled materials – another current trend.  His home landscape sports a retaining wall constructed of granite from Victorian buildings torn down in Rio in the 50’s to make way for modern buildings that had taken over the public’s desire.  This reuse of existing materials is an important component of sustainable landscape design today.

Recycled Victorian granite built into a retaining wall at Roberto Burle Marx sitio in Brazil.

The UD students on this study abroad not only walked through Roberto Burle Marx designed gardens, but biked through the famous Flamengo Park, also designed by Burle Marx, and intended to provide people of Rio de Janeiro a place to relax and enjoy nature in the midst of one of the biggest cites in the world.  The park uses groupings of trees and shrubs as well as rolling topography to create private spaces for people to enjoy a wide variety of outdoor activities.

In the US, we are proud of Central Park in NYC, but Rio de Janeiro boasts 2 of the world’s largest urban parks. Tijuca Park was once denuded for timber and then planted to sugar cane followed by coffee.  When the soil could no longer sustain crops and started to wash down the mountainside, Brazil replanted the forest and it is enjoyed today by many people and animals. Unfortunately, it was planted to mostly non-native species, so Brazilians cope with some of the same invasive plant problems we face in the US.

Roberto Burle Marx has a special place in the hearts of gardeners in the Delaware Valley, because his only landscape design installed in the United States is at Longwood Gardens.  The Cascade Room at the end of the Acacia walkway and past the orchid display features waterfalls and bromeliads and was designed by Burle Marx near the end of his life.

The Cascade Room at Longwood Gardens during the 2019 Christmas display with its bold bromeliads.

Our students learned much about landscape architecture and the culture of Brazil.  What are the take home messages for all gardeners?  Celebrate native plants of your region.  Be artistic in your planned landscapes (in whatever form you wish to express yourself).  Reuse and recycle materials to make sustainable landscapes.  And finally, create gardens that people can enjoy.  Touché’ Roberto Burle Marx, your legacy lives on in the minds of many and especially in the 14 UD students who are wiser after this winter session for having learned about your work.

For more information about horticulture in Delaware visit and follow me on Instagram at sbartonhort.  The Sue Barton blog has a calendar of events that includes many interesting meetings, workshops and webinars for interested gardeners and landscape professionals.  Check it out!



Why Landscape Design?

As we cross over from summer into fall, there is still time for planting, but there is also lots of time to think about revising your landscape next year.  Maybe you think your landscape is perfectly acceptable, like those around you and simply not in need of any revision.  That may be the case, but there are also several reasons why you might want to consider a landscape renovation.  Do you ever renovate the inside of your house?  How old is your kitchen?  How about bathrooms? When was the last time you bought new curtains, a new rug or applied a fresh coat of paint?  We take many home renovations for granted, without every really thinking about renovating the outdoors.

Think about whether your landscape truly provides spaces for you to enjoy the outdoors or is it simply a decoration of the front of your house? An effective landscape creates outdoors rooms in which you and your family can live, especially now in Delaware when the outdoors is such a pleasant place to be! But, creating outdoor rooms doesn’t just happen. You need a floor—a nice lawn area, patio or deck.  You need walls—shrubs or small trees that block some views and accentuate others.  And you need a ceiling—large trees that overhang your room and provide a sense of enclosure.

Another reason to renovate your landscape is to make sure your outdoors is providing the ecosystem services you need to live.  Ecosystem services include clean water and well-managed water.  Does the water that falls on the roof of your house or your driveway stay on your property and infiltrate, where it can become cleansed by flowing through the soil and making it to the groundwater?  Or does water flow off your property into storm drains carrying debris and other pollutants to our surface waters? You can design your landscape to keep all the water on site and allow it to infiltrate to water your plants and slowly recharge the groundwater of Delaware.

Another important ecosystem service is clean air.  Plants take in carbon dioxide and give off oxygen, of course, but they also remove undesirable particulates from the air.  While turfgrass is a plant and does give off oxygen, it is not as good at supplying oxygen and removing particulates as a more complicated multi-layered landscape.  If you have lawn plus groundcovers, perennials, shrubs, small trees and large trees, you are intercepting and cleansing air at many different levels or layers within your landscape.

A third ecosystem service is wildlife habitat.  We have all been hearing how important it is to provide plants for pollinators to pollinate our food crops, but in fact, every plant needs to be pollinated in order to survive.  Also, plants are the basis of the food chain.  Without plants we would not support insects and without insects, we can’t support birds, without birds we can’t support carnivores that eat birds, etc. It turns out we need not just any plant, we need native plants.  Native plants and native insects have developed close relationships over evolutionary time, so if we want to have enough insects to feed baby birds (and who doesn’t want to invite birds into their landscape), we need to plant native plants.

The fourth ecosystem service is human wellness.  Spending time outdoors is a great stress reliever and is important to a happy, healthy life.  Creating landscapes that make it fun to be outdoors will restore your mental capacity to deal with that tough problem you are facing at work or at home.

So where does landscape design come in?  Creating landscapes that fulfill these ecosystem services takes skill and experience.  Landscape designers and landscape architects have been trained to think in terms of creating outdoor rooms and functioning landscape that do more than just look pretty.  At the University of Delaware, we are training students in our Landscape Architecture program for careers in which they can help homeowners, businesses, and communities create functioning landscapes that meet the needs of the users and provide the ecosystem services we all need to survive.

A group of landscape architecture students at UD is hosting the second Landscape Architecture Symposium sponsored by the program (and by the Delaware Center for Horticulture).  The Craft of Design: Enhancing Skills and Landscape Function will be held on November 1 (8 AM – 6 PM) at the Delaware Center for Horticulture in Wilmington, DE.  Speakers will talk about people-centered landscapes and afternoon workshops will work on building landscape skills in sketching, photography and modeling.  This symposium is open to anyone who is interested in landscape design and would be the perfect opportunity to help you jump start a garden renovation project at home.  For more details and to register visit

This low retaining wall and perennial provide a “wall” for an outdoor seating patio. Plus lots of native plants provide food for native insects encouraging birds and other wildlife.

Tall, arching trees provide a sense of enclosure in this backyard patio.

Control those weeds!

A major summertime gardening task is controlling weeds.  Especially this year, with all the rain we’ve had, weeds are running rampant in many gardens.

The best way to control weeds in the garden is to prevent them from growing in the first place.  Planting desirable plants close together to cover the ground is the most natural and effective method of weed control. Some people seem to think vast spaces of mulch are beautiful, but ideally mulch is a temporary ground cover until plants fill in. That said, mulch spread to a thickness of one to three inches will prevent many annual weeds from germinating.  So, mulch is better than bare soil.  Anyone who has managed a vegetable garden knows that bare soil will become a bed of weed seedlings in a few weeks with sufficient rain. Keep mulch away from tree trunks, where is will rot the bark and open wounds for disease and insect entry.  And don’t let the mulch get thicker than about 3 inches.  We want plant roots to grow in the soil, not the mulch.

Another method of preventing weeds is to use a preemergent herbicide.  Crabgrass is controlled in the lawn with a preemergent in early to mid-spring.  Unfortunately, in a rainy year it may be necessary to reapply crabgrass preemergents to keep the herbicide barrier in tact and prevent weed seedlings from emerging. Summer annuals can also be controlled in landscape beds with the use of a preemergent herbicide, but it must be applied before the weeds come up. I have effectively controlled Japanese stilt grass in some areas of my landscape by applying a preemergent in early spring.

Finally, weed fabric. black plastic or even newspaper can be used in the vegetable garden to either smother or prevent weed emergence.  We have a large vegetable garden created by the former land owners and since we can’t use all the space, rotate areas to cover with black plastic for a season.  We let leaves and weeds decompose and usually have great soil for the following year as we rotate planting areas.  We have also learned it is well worth the time to plant tomatoes and peppers in rows and use weed fabric in between.  There are fewer weeds and a good surface for walking on to pick your produce.  This year we seeded corn, beans and other veggies in rows spaced perfectly to allow us to put down weed fabric once the crops germinated.  When putting weed control in an area where you are growing plants, you must use a permeable fabric, not black plastic, so water gets to the plant roots.

We already know “on ounce of prevention is worth a pound of cure” (Benjamin Franklin), but if you have weeds already growing in your garden, prevention is not an option.  There is a school of thought that says it is better to spot treat with an herbicide than to disturb the soil by pulling up the weed.  That makes sense when you think about how many weed seeds are present in soil (130 million weed seeds in a plow acre in a Minnesota study). When you pull up a deep-rooted weed, you disturb the soil, bringing new weed seeds to the surface.  By spot treating with an herbicide, no additional weed seeds are exposed.

Another school of thought believes in regular tillage when weeds are young to desiccate those weed seedlings. I admit, it is a lot easier to pull weeds as you see them than to mix up herbicides whenever you want to attack your weeds.  Probably for most people, a combination approach makes sense.  Be sure when you pull weeds to use a trowel and get the entire root. Another strategy is to use a flame torch to control weeds.  We had to buy a torch to seal some roofing material, so we started experimenting with it in the vegetable garden.  It burns off the weed tops but does not kill the roots.  Although with young plants and repeated use, it does a pretty good job. Be careful not to burn desirable plants. This method is best used for cleaning up larger spaces in a vegetable garden prior to seeding.

When you spot spray for weeds in the garden, be sure to spray on a calm day and use a spray nozzle that allows you to carefully direct the herbicide to the weeds you are targeting and avoid desirable plants.  There has been much written about glyphosate (sold by Monsanto as RoundUp) in the news lately.  I suggest you consider the source of the information you are evaluating.  Many people believe that since two juries have found RoundUp at fault in causing the plaintiff’s cancer, it must be a cancer-causing chemical.  Everyone has the right to make their own decision, but for my money, I will believe the data from over 100 research studies that support the belief that RoundUp does not cause cancer, before I will believe 24 jurors, most of whom are probably not scientists, who were convinced by a lawyer (also not a scientist) that RoundUp does cause cancer.  What I can tell you for sure, is to avoid “home remedies” for weed control.  There are many substances we have in our kitchen or bathroom cabinets that are toxic to humans and bad for the environment.  Do not mix up your own brew to control weeds, no matter what you read on the internet!

Use plant masses and a bit of mulch at the edge to prevent weeds.

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