Maryland Grows

Featured Video – Container Gardening

Container gardening is a great way for beginning gardeners to start producing their own food. Jon Traunfeld from the University of Maryland Extension talks about everything you need to know, from potting soil to planting, to grow vegetables in containers. From five-gallon buckets to Earth boxes, container gardening gives you options for any budget.


Black Covers Can Put Weeds to Bed… For Good

Have you experienced one or more of these garden scenarios?

  • It’s early April and chickweed, henbit and other winter annual weeds are growing so thickly in a vegetable or flower bed that the soil can’t be seen.
  • The winter rye cover crop you mowed last week is growing back.
  • You tilled and raked a bed that you couldn’t plant right away and now weeds are coming up everywhere.
  • The rainy summer weather is favoring weeds over crops so that the weeds are taking over walkways and dominating beds that you want to plant with fall crops.
  • Neighboring plots in your community garden have been abandoned and weeds are growing wild and reproducing!

I can’t bear to look… I’m going back inside

This stirrup hoe is great at removing large weeds, but brings lots of weed seeds up to the top two inches of soil where they have a good chance of germinating.

Un-controlled weeds compete with garden plants for water and nutrients, are hosts for insect pests and diseases, and can demoralize the toughest gardeners. Tilling, pulling, chopping, and hoeing are all fine weed control techniques under the right conditions, but they also disturb soil allowing even more weed seeds to germinate and flourish.


There’s another way: occultation. The common dictionary definition is “an event that occurs when one object is hidden by another object that passes between it and the observer.” For gardeners and farmers, it’s covering the soil to create a dark, warm, moist environment. In 2-4 weeks, this no-till technique can

  1. smother and kill young weeds
  2. smother larger weeds and grasses
  3. accelerate the decomposition of mowed cover crops and weeds
  4. promote the germination of weed seeds and then smother the seedlings

Weed barrier pinned down over a bed filled with winter annual weeds. It was ready to plant in two weeks. Tough perennial broad-leaf weeds and grasses may be weakened but not killed.

When the cover is removed you are left with a mat of decaying organic mulch. New weeds will be fewer because the soil was not disturbed. Spread a 1-inch layer of compost and you’re ready to plant seeds or transplants. Of course, you could plant transplants through holes cut into the weed barrier.

Weed barrier used to cover mowed cover crop in spring. The weed barrier strip on the left was removed three weeks later and tomatoes were planted in the decomposing residues.

Gardeners can use black tarps or weed barrier fabric. Some farmers use black silage covers (new or used). Weed barriers allow water and air to penetrate while tarps and silage covers are water-resistant. I’m not aware of research that has compared the types of covers used in occultation. I’ve had good luck with heavy-duty woven polypropylene weed barrier fabrics (they last for many years). Four-foot widths work well for most gardens and strips of the fabric can be overlapped for wide beds. It’s important to completely cover the target area and pin down the edges of the cover with landscape staples, bricks, or soil. If possible, weed-whack or mow the weeds first. DO NOT cover the fabric with any organic material. Weed seeds will germinate on top and grow roots down through the weed barrier.

By Jon Traunfeld, Director, Home and Garden Information Center 

Additional information: this technique was explored in a research project by Jerry Brust, Ph.D., IPM Vegetable Specialist.

Spring Lawn Care: How to Deal with Weeds and Bare Spots

forsythia shrub in bloomWith spring gardening season right around the corner, lawn questions have been rolling in to the Home & Garden Information Center (HGIC). Here I’ll address some of the most common questions about weeds and overseeding.

Dealing with Winter Weeds



In late winter/early spring, we typically see winter annual weeds in thin, under-fertilized, wet, or shady areas. These weeds germinated in the fall and will die as the weather warms up later in the spring. In my observations, this has not been a particularly bad year for winter annuals. They are favored by wet, mild winters and I think we had just enough “bitter cold” in January and a fairly dry stretch through December and January to reduce populations.

Typical winter annual weeds include chickweed, henbit, purple deadnettle, and shepherd’s purse. Options to address these winter annual weeds include hand pulling, spot spraying with a broadleaf herbicide, or waiting until they die once weather climbs to the 60’s and 70’s on a regular basis. For perennial weeds like dandelion which will start to re-emerge later this month, hand-pulling or spot spraying are the best methods for control.

Crabgrass Management


Large Crabgrass

Crabgrass is native to the tropics and in Maryland is considered a summer annual since it germinates in spring once soil temperatures reach 55-57° F. The typical phenological (plant-based) indicator of 50°F soil temperature for applying crabgrass pre-emergent products coincides with forsythia near or at peak bloom. I know a lot of homeowners consider applying crabgrass pre-emergent somewhat of a rite of spring lawn care without thinking much about some of the other factors involved in crabgrass control. I would encourage you to think more about this than automatically going out to apply herbicide.

There are other important lawn management factors that contribute to reducing crabgrass encroachment in the lawn. As a summer annual, crabgrass likes areas that are warm and sunny and takes advantage of open spaces. In a lawn, this would include bare and thin areas where the grass is either non-existent or struggling. So what does this mean when it comes to maintenance practices?

Most importantly, “mowing high” and fertilizing correctly to encourage dense grass cover are two of the most important maintenance practices you can do to combat crabgrass invasion. Tall fescue lawns should be mowed at 3 – 3 ½”. This helps encourage a deeper root system and creates a cooler, shadier microenvironment at the soil surface. University of Maryland research has shown that plots mowed at 3 ½” with dense grass cover typically only had a few percent crabgrass even when no crabgrass pre-emergent products were applied.

Overseeding Bare Areas

While seeding is most successful in the fall, overseeding thin or bare areas in the spring to help increase density is an option. Tall fescue grass seed doesn’t need as warm of temperature as crabgrass, so you may consider trying to overseed in late March/very early April before crabgrass germination gets into full swing. Keep in mind, however, that any pre-emergent product you apply for crabgrass will also prevent tall fescue seed from germinating.

If you’re interested in learning more about lawn care, I will be presenting a “Bay-Friendly Lawn Care Practices” workshop and tour of the ‘Grass Roots’ turfgrass exhibit at the U.S. National Arboretum in Washington, DC on Saturdays, April 7 and May 12 from 10 a.m.-noon. In this workshop, I present a comprehensive strategy for lawn care best maintenance practices for the year in an integrated pest management framework. If you would like to register, please contact me at

Additional Resources 

By Geoff Rinehart, Lecturer, Turfgrass Management, Institute of Applied Agriculture, University of Maryland

I’m Lichen It! – Peak Season for Lichen Peeping

St. Paul's Episcopal Church, Hillsboro MD Beard lichen on branch of flowering dogwood tree.

Beard lichen on dogwood trunk, Caroline County MD

The wet, gray days at the end of winter seem like they may never end. But this is actually the perfect time of year to get out and appreciate those mysterious ‘plants’ encrusting everything from sidewalks to treetops – the lichens.

There is a lot to be said for simply enjoying the natural beauty of lichens without trying to label them. However, lichens are easier to identify, at least to the family level, than you might think.

If you can distinguish soil, rock and tree bark, you are off to a running start. Different lichen species specialize in growing on these three types of substrate, so this is an important first clue to a lichen’s identity. Hunting for lichens at this time of year is facilitated by the general lack of foliage, making bare soils, rock outcrops, and tree trunks more visible than usual.  As a special bonus, storms have littered the ground with lichen-encrusted branches, revealing treasures that would normally be above our reach. Even small branches can host several species, each with its own unique color and shape.

Body shape is another clue that is easily understood by beginners. Lichens occur as either:

  • Powdery, crusty colors on surfaces, reminiscent of spray paint.
  • Flat leafy shapes, usually rounded in outline.
  • Three-dimensional shapes reminiscent of shrubs, beards, cups, etc.

Crustose lichens

Crustose lichens on tombstones, Caroline County MD. Field of view 1″ wide

Color is another easy clue, and it is during gray, wet weather (typical of March) when lichens are most colorful. During dry spells, lichens shrivel up and their surfaces become opaque and faded-looking. This protects the internal, photosynthesizing algae from desiccation. When re-moistened, lichens expand and their surfaces become transparent again. Light and moisture can reach the internal algae, and photosynthesis resumes. The algal colors, which are often brighter than that of the fungal surface, shine through.

Lichens produce special structures for dispersing their progeny, and these result in interesting changes in shape, texture, and color which are further clues to a lichen’s identity. The reproductive lives of lichens are unique, involving asexual methods, as well as sexual reproduction of the fungal symbiont. As with many things botanical, these structures have intimidating names like insidia, soredia, and apothecia. Fortunately, it is not necessary to remember the names of the dispersal structures to use them successfully as taxonomic clues.

The life cycles of many native animals are intricately tied to lichens. Here are a few examples from animals native to Maryland:

Lichens also have many other stories to tell, intertwining their presence in almost all aspects of ecology and human endeavor. Here are but a few examples that illustrate their importance:

  • Approximately 8% of the terrestrial earth is covered by lichens.
  • Lichens absorb nutrients from the air and can be used as air quality indicators.
  • Lichens contribute nitrogen and minerals to the ecosystems in which they occur.
  • Historically, humans have used various species of lichens to make dyes and medicines.
  • Lichens produce unique biochemicals to fend off herbivores, prevent freezing, and stop seeds from germinating in their soft, moist tissue. These chemicals hold promise for the development of new medicines and agricultural chemicals.
Sunburst lichen

A diminutive (1/2″) sunburst lichen and companions on a tombstone in  Caroline County MD.

Speckled shield lichen

Speckled shield lichen growing on tree trunk with moss.

When you can’t get outside, here are some ways you can explore the world of lichens from the comfort of your armchair:

  • Take a photo tour on the Maryland Biodiversity Project. Click on the icon for thumbnail images, and then click on the icon for slideshow. Enjoy!
  • Get Lichens of the North Woods: A Field Guide to 111 Northern Lichens by Joe Walewski. This affordable little field guide is for beginners. The introduction includes a very readable overview of lichen ecology, reproductive biology, and human uses. A simple system of three substrates and three basic shapes allows you to quickly start keying out lichens.
  • Guide to the Lichens of Howard County, MD  (6mb pdf) by Richard Orr. Beautiful 664-page guide to local lichens with color photographs. Free!
  • Get a big, beautiful picture book, Lichens of North America, by I. Brondo, S.D. Sharnoff, and S. Sharnoff.  Also contains in-depth descriptions of lichen biology and a detailed key to the 3600 species found in North America.

By Sara Tangren, Ph. D
Agent Associate | Master Gardener Trainer | Sustainable Horticulture and Native Plants

Do you have concerns about lichens on landscape plants? Don’t worry! They do not harm plants. See Lichens-Trees & Shrubs on the Home & Garden Information Center website.

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Lawn and Garden Tips for March


Ornamental Plants

  • Starting Seeds Indoors – Many types of annual flower plants can be started indoors this month. Generally, most are started 5-6 weeks before they are planted outdoors.
  • Spring bulbs are emerging and some are even flowering at this time. Exposed leaves may be burned later by very cold temperatures but the spring flower display will not be adversely affected.
  • Groundcovers are arriving in local nursery and garden centers this month. They are a great alternative to grass where grass won’t grow, where you have heavy shade or tree root problems and on steep slopes.

Read More

A Swede By Any Other Name

A Master Gardener friend who recently traveled to the UK brought me back a packet of seeds. Specifically, ‘Gowrie’ rutabaga seeds from a company called Mr. Fothergill’s.


Except because these are British seeds, they’re not called rutabaga, they’re called swede. The packet does include the botanical name of the plant (Brassica napus napobrassica) so if you’d never heard of swedes and didn’t recognize the picture, you could look them up – I hope all our American packets of rutabaga seeds do the same!

This got me thinking about vegetable names that separate us by a common language, or divide us by different ones, or in general confuse us. I’ll give a few examples below, and please tell your own stories of vegetable name mix-ups in the comments.

Read More

Q&A:  Why didn’t Japanese maples lose their leaves last fall?

Japanese maple with brown leaves

This Japanese maple retained dried leaves during the winter. Photo: D. Ricigliano

Q:  Most of my Japanese maples are still full of dead leaves. They never exfoliated in the fall to leave bare branches. Will this affect new growth in the spring? Should I just let them be?

A: We have received several questions about Japanese maples that are still holding on to brown leaves that didn’t drop last fall. Some crapemyrtles also have held their leaves during the winter. This issue has been reported in several areas of Maryland, which suggests it is due to an environmental factor. An unusually warm autumn followed by a quick cold snap likely interfered with the trees’ normal winter preparation processes.

As the days shorten in the fall, trees go through a series of biochemical and physical changes to prepare for winter survival. In deciduous trees, this includes the development of an abscission zone of cells where the branches connect to the base of leaf stems (petioles). A layer of cells essentially seals off the branches to protect them from water loss, and then the leaves are shed from the tree. We suspect the fall cold snap interrupted this process and normal leaf abscission did not occur in some trees.

Some types of trees naturally do tend to retain dead leaves during the winter. American beeches and many oaks exhibit this trait, called leaf marcescence. This occurs most often on juvenile trees. It may be a strategy to protect buds from winter damage or to discourage deer browsing. Trees may also wait until spring to shed their leaves, thus providing a fresh source of nutrient-rich organic matter to the root zone where soils are otherwise poor. The exact reasons for leaf marcesence haven’t been determined completely.

There is nothing you need to do for your Japanese maple at this time. If your tree was otherwise healthy, new growth will emerge in the spring and the old brown leaves will drop off eventually.

Sources and Additional Resources

By Christa Carignan, Coordinator, Digital Horticulture Education, Home & Garden Information Center

Have a plant or pest question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask an Expert.