Gardening Questions in May

Q: I have a few English Bluebell plants in my garden. Their leaves are now flat and yellow. What if anything is wrong with them?

A: I am not sure what you mean by English bluebells. Virginia bluebells (Mertensia virginica) are early blooming spring flowers in this region. They are a spring ephemeral, meaning they come up and flower in the spring and then die back to the ground later in the season. Most bluebells have yellow leaves now and eventually they will die back completely until they come up again next spring.

A reader responded to this question with information about English bluebells. The Latin name is Hyacinthoides non-scripta. She noticed at Winterthur last week they had both Virginia bluebells and Spanish bluebells (Hyacinthoides hispanica), and the latter look almost exactly the same as the English ones. She tried for years to get Virginia bluebells to grow in her suburban Wilmington garden without any luck so finally gave English bluebells a try and they have been great. They have beautiful blue flowers that last for several weeks in the spring.  In her garden, the flowers are now past, but the foliage is still bright green, though mostly flatter than upright at this point. They will go brown later on and fade away as do the Virginia bluebells, but it does seem early for them to be turning yellow.  She ponders — perhaps it depends on location and amount of sun, since they will grow from full sun to full shade, and mine are mostly in shady places.

My response is this confusion is often the problem with common names.  I know that plant as Endymion non-scripta and have called it scilla as a common name.  I see that Hyacinthoides is the correct scientific name.  I still think it is more likely that Virginia bluebells (Mertenisa virginica) would be turning yellow now and fits the description of large flat leaves.  Hyacinthoides has narrow linear leaves.  Both plants are great in the garden!

Q: Please help me to identify this very sweet smelling bush that is growing near my home.

A: The shrub in question is Elaeagnus umbellata or Autumn olive. It is very sweet smelling, but it is an exotic invasive species and should be removed. It invades natural areas and displaces native species. Here is a fact sheet about autumn olive.

Q: I have several Berberis thunbergii “Aurea” bushes planted on the south-east facing side of my house. They suffered what looks like frostbite from the ice storms we had this past month. Will pruning this spring bring them back to health or do I have to treat then with some kind of solution?

Also I have a row of 20 arborvitae on the north facing side of my house that seem have suffered the same kind of damage near the bottom of each plant. Only the very bottom branches of the trees have turned brown. They are all about 7 or 8 years old. Again, do I need to treat them with anything or should I cut the brown limbs off?

A: There is nothing you can apply to correct winter damage. The only solution is to prune back the dead or damaged tissue. With the barberry, they can be pruned hard and they will grow back. But, remember Japanese barberry is on the invasive plant list in Delaware. Maybe you want to take this opportunity to replace them with a better plant. Here is a publication that lists alternatives to Japanese barberry ( The lower limbs of the arborvitae should be pruned, but they probably won’t regrow at the base of the plants.

Selecting the best plants for your garden


Hooray! Spring is really here with its rainy days, windy days and beautifully sunny days.  So, it is time to visit the garden center and buy new plants for your home and garden.  Many people want help in selecting just the right plant for their particular location.  Plant selection is tricky and should be based on a number of factors.  First and foremost, evaluate your planting site.  Does it get full sun, partial shade or is it shady all the time?  Is it dry, moist, well-drained?  Is the soil sandy or clayey?  Are there competitive plants nearby?  Are there walkways or buildings close to the planting space?  All these factors should be considered when selecting the best plant for any landscape.  Remember to learn how large a plant is expected to grow; don’t expect the plant to stay the size and shape it is when purchased.  Think about when and how long it blooms or what fall color and winter interest can be expected.  It is easy to walk around a garden center and be wowed by the plants that are in bloom, but they are not likely to bloom all season, so you should also enjoy the habit, bark, leaves and branch structure of the plant.

Most people select plants based on ornamental characteristics like flowers, fruit, fall color, bark and interesting branch structure.  Those are important and should be considered when choosing a plant to occupy space in your landscape.  Think also about how it will be viewed.  Is the plant going to be viewed from a distance, where fall color and habit can play a big factor or is it going to be located right next to your patio where fragrance might be most important?  Maybe a tree should be selected that will provide shade or screen an unsightly view.  Really think about what you want the plant to “do” in your landscape.  That will help narrow your choices.  Of course, start with plants you like, but then focus on the functions the plant will perform.


So far, we’ve been talking about traditional landscape design principles.  But, I propose there is another set of factors you should consider when selecting a plant for your landscape—the ecosystem services that plant will provide.  All plants provide some ecosystem services such as taking in carbon dioxide and giving off oxygen; absorbing pollutants from the air; and taking up water, breaking the fall of raindrops and having root systems that allow water to filter into the surrounding soil. But, not all plants are created equally when it comes to some ecosystem services.  Especially when it comes to wildlife habitat, native plants are superior to exotic plants.  Most plants have evolved defense mechanisms to protect themselves from predation (getting eaten by insects), but plants and insects that have evolved together over many thousands of years have special relationships that allow insects to find food in their native environment.  A good example is the Monarch butterfly whose larvae are able to consume milkweed, even though the milkweed contains a chemical toxic to most insects.  This relationship is so important to these specialist insects that they won’t survive without the native milkweed they have evolved to eat.  So, if you want to support a diverse population of wildlife with your home landscape (and you should), consider including a variety of native plants in your selections this year.

Is It Really Spring?

Many people think spring is the time for lawn care.  Actually, there is not much you need to do for your lawn in spring other than cut it once it starts to green up and grow.  Lawn fertilizer should be applied in the fall, when plants are putting their energy into growing healthy root systems.  Fertilizer applied in the spring, promotes top growth, which you just have to cut.  It also promotes lawn weeds.  In the spring, lawns are battling the winter annual weeds that persist, like chickweed and will soon be battling the summer annuals, like crabgrass; not to mention the broadleaf perennial weeds, like dandelion.  Fertilizing in the spring, helps those weeds compete with the desired grass in your lawn.  If you want your lawn to green up quickly in the spring, it is OK to add about ½ lb of nitrogen per 1000 square feet.  That is equivalent to applying 25 pounds of a 21-3-3 (21% N) fertilizer to a 10,000 square foot lawn.

If you don’t want to worry about when to fertilize and how much fertilizer to use, consider hiring a Livable Lawns Certified lawn care company this spring.  Visit the Livable Lawns website to learn more about caring for a healthy lawn and to find a certified business near you –

The Livable Lawns program can also help you with the other task you might be contemplating as spring gets nearer—new planting.  Consider planting native species.  Native plants have a special relationship with native insects.  Most insects are specialists and feed on only one or two species of plants with which they co-evolved.  If we want pollination services and lots of other ecosystem services provided by a biodiverse ecosystem, we need to include native plants in our home landscapes.  That is certainly not a hardship since many native plants have great flowers, fruit, fall color and all the ornamental characteristics we desire in our gardens. Lots of people have been feeding the birds this winter and look forward to the return of more birds as the weather warms.  Did you know that while adult birds can eat seeds, baby birds can only eat insects?  Without our native insects we can kiss our native birds goodbye.

If you hire a certified Livable Lawns lawn care company you can receive a $50 gift certificate to purchase native plants at participating nurseries and garden centers.  If you want to apply fertilizer to your lawn yourself, visit the Livable Lawns website.  Read through the 8 requirements and sign on the dotted line. Once your application is received, you will get a free soil test kit and your reporting sheet. Fill out the sheet as you fertilize throughout the fall and once you turn it in, you’ll receive a free $50 gift certificate for purchasing native plants next fall.

Livable lawns


DNLA Plants of the Year – 2015

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 2015 selections were just announced at the Delaware Horticulture Industry Expo in Dover.

 Eurybia divarcata (Aster divaricatus)             White Wood Aster

This fantastic native ground cover can be found from Maine to Georgia in deciduous woods and along roadsides.  White wood aster has heart-shaped leaves borne along thin, purple-black cascading branches.  The cultivar ‘Eastern Star’ is shorter than the species and has deep dark shining mahogany stems. Small star-like white flowers with yellow centers are borne in profusion from mid-July into early October.  It is one of the few asters that grows in the shade, but takes sun as well, so in a new planting under young trees, the white wood aster will thrive and continue to thrive as the trees cast more and more shade.  White wood aster grows in average to dry soils, and works well as a ground cover at the edge of the woods or at the front of a border growing through other plants.  It attracts butterflies, is somewhat deer resistant and makes a good filler in a cut flower arrangement.


Ironwood, the woody selection, turns a beautiful bronze color in fall (photo credit: Rick Darke)

Ironwood, the woody selection, turns a beautiful bronze color in fall (photo credit: Rick Darke)

Carpinus caroliniana  Ironwood

Ironwood is a small-medium sized, wide-spreading tree that is native to the eastern half of the United States.  Ironwood, sometimes called Blue Beech or Musclewood, is named for its thin, bluish grey, sinewy bark that looks like flexed muscles.  Leaves are pointed, serrated and dark green, often lustrous, in summer and change to yellow, orange, red, and reddish purple in fall. Ironwood can be difficult to transplant and should be moved balled and burlapped or from a container in late winter to early spring.  This handsome tree is usually found as an understory plant along rivers and streams, where it withstands periodic flooding. Michael Dirr has seen this tree in a wide variety of landscape settings and believes it is quite adaptable.  This tree has a lot to offer our landscapes in subtle beauty.

Preventing Winter Injury

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The cold spell we had in mid-November was a good wake-up call that winter is on its way.  The question is “Are your plants ready?”  In most cases, the answer is “yes.”  Plants that evolved in the mid-Atlantic are prepared for winter by dropping their leaves or dying back to the ground completely, in the case of herbaceous perennials.  Needle evergreens have evolved narrow leaves with coatings that prevent moisture loss in the winter to help them survive.  The real problem is with broad leaved evergreens.  In a recent talk at the Delaware Ornamentals and Turf Workshop in Hockessin, DE, Jason Veil, curatorial intern at the University of Delaware Botanic Gardens, pointed out that of the 50+ broadleaved evergreens we commonly plant in Delaware, only 4 are native.  Very few broadleaved evergreens have evolved to handle our weather.

When we think about winter injury, there are a few factors in play.  First is the genetics of the plant.  It is important to know where the plant evolved.  Red maples grow from Florida to Canada.  Seeds from Florida red maples may not be hardy in northern states.   Most cultivars are selected for their ornamental characteristics, but environmental characteristics, such as cold tolerance, moisture tolerance etc. are even more important for planting success.

With broad leaved evergreens, the most common winter injury is leaf scorch–dead areas on the leaves.  This is caused by water loss during the winter.  Moisture is lost from the leaves, the wind blows the moisture away from the leaf surface and the leaf loses more moisture. Wind can’t be changed, but you can locate plants to avoid prevailing winds when planting broadleaved evergreens.  Excess sunlight is also a problem.  The sun can warm up the leaf, tricking the plant into losing more water.  So, plant broadleaved areas in spots that are protected from the wind and winter sun.  Since moisture loss is the major cause of winter injury in broadleaved evergreens, fall rains are important to build soil moisture. When you complain about that cold, wet day; remember how good it is for our plants.  If we have a dry fall, it may be necessary to water tender or newly established plants during the fall.  Fortunately, this fall we’ve had plenty of rain.

In Delaware, plants acclimate to the cold weather by “hardening off” in response to shorter days and colder fall temperatures.  Acclimation is a slow, steady process.  After a 2-month chilling period has been satisfied, deacclimation can occur pretty quickly in spring.  If we get some unseasonably warm weather in late February, plants can break dormancy before our cold weather is really over.  We’ve all seen cherries or magnolias start to bloom early and then get damaged by normal cold weather that follows. Loss of flowering is a nuisance, but deaclimation can cause even more severe injury when we get a warm spell in late winter.

Not all plant parts have equal cold tolerance.  Stem tissue is the most tolerant part of the plant.  Vegetative buds are next because the plant needs these buds to grow.  Flower buds are less cold tolerant; we want flowers but they aren’t as necessary for plant survival.   Interestingly, while they are critical to plant survival, roots are least cold tolerant because they are normally buffered by the soil.  Plants in above-ground containers are not as cold hardy as that same plant would be in the ground.

For winter hardiness, avoid top growth and promote root growth in the late summer and fall.  Avoid pruning and fertilization that would push new, tender growth.  Avoid planting perennials in the fall when there isn’t enough growing season left for them to establish a healthy root system before they have to tolerate the alternate freezing and thawing that occurs during a Delaware winter.  Evergreens don’t grow roots in the fall, so it is best to wait until spring to plant evergreens.

Salt is another important factor in winter injury.  Plants close to salted roads or sidewalks get the double whammy of cold temperature and salt injury.  For those locations, pick salt tolerant plants, like groundsel bush, eastern red cedar, bayberry and any other plant that grows well at the beach.

So, what can you do to prevent or reduce winter injury?  Start by selecting cold tolerant or salt tolerant plants.  Place those plants to avoid winter sun and wind.  Consider protecting broadleaved evergreens by planting in shaded locations, such as the north side of a building. Avoid late season fertilization and pruning and fall planting of evergreens.  Irrigate during dry spells in fall or before cold snaps.  Apply mulch to young or tender plants to help protect roots   Consider placing evergreen boughs over small tender plants for winter protection.  Some people wrap their evergreens in burlap to protect them from winter injury.  I have to admit that doesn’t make sense to me.  If you planted an evergreen, you chose it because it stays green all winter, why would you cover it up?  It is best to select plants that tolerate our weather conditions.  If you “push the envelope” as many gardeners so, be prepared to replace tender plants after a tough winter.  Who knows what the winter of 2014/2015 will bring.  We can only wait and see.

Meadow responses

I received a lot of responses to my meadow column in the News Journal.  Here is one of the responses with my answers:

I read your article “Would a meadow a home work for you” in The News Journal, dated Saturday 7/26 suggesting I could start a fairly large “Meadow” by not cutting your front lawn and let nature “seed”, transform, the lawn area into a meadow.

I like the benefits of this concept eg: reducing the costs of cutting the grass, less watering, chemicals, and the increased rain water saturation to the and so, and I am interested but, I have a few questions before proceeding;

1. “won’t the lawn just turn into a weed patch of crabgrass, thistle, plantain, etc. when I stop cutting my grass”?

2. “what will prevent the weeds from crowding out the grasses and flowers mentioned in the article”?

3. “how can I control the spread of the weed seeds to my neighbors”?

4. “do you know if a “meadow” affects the value of my home considering right now all of my neighbors have lawns?

Great questions.  What the “lawn” becomes is highly dependent on what is currently in the lawn and the plants nearby.  If you currently have a vigorous stand of cool season turf, you will just get a taller stand of cool season turf.  Crabgrass is not a problem in a meadow, because the seed needs light to germinate.  Unless, you have many open patches in your lawn currently, the taller grass pretty much excludes light from reaching the soil and crabgrass will not grow.  In fact, crabgrass is less of a problem in a meadow than in a mown lawn.  Thistle could be a problem if you have it nearby.  It would need to be treated with an herbicide to get it under control.  Lontrel is recommended for use on Canada thistle. Plantain would be a relatively desirable component of a meadow. Its seed heads are interesting and it isn’t a problem plant.

Grasses are fairly competitive, so once you have a good stand in place they will do a good job of competing with incoming weeds.  I guess that also depends on what you define as a weed.  Many lawn weeds are not really weeds in a meadow.  Woody plants can be controlled in a meadow by mowing once or twice a year.

If the meadow becomes more diverse with age, which it will naturally do, there may be seeds that your neighbor would define as weeds.  But, there are probably natural areas, roadsides etc. that are already contributing weed seeds to your neighbor’s property.  You won’t be increasing that dramatically by having a meadow.

If you want a really great meadow that is comprised of warm season grasses and a few desirable perennials, it is best to seed the meadow with the plants you want.  Eventually warm season grasses will probably come into the meadow on their own.  Switchgrass (Panicum virgatum) grows extremely well in southern Delaware and may become a component of your meadow over time.  Or you could seed it into the lawn and jump start the process.