Splashy Groundcovers, Bulbs Announce Spring

Veronica pectinata's blue blossoms complement spring-blooming bulbs.

Veronica pectinata’s blue blossoms complement spring-blooming bulbs.

In spite of recent snowfalls in Denver, spring has finally arrived.

It all started with the crocuses.  Soon other harbingers arrived, including Corydalis ophiocarpa, which is outdoing itself this year with its cheery, long-lasting blooms.

Some literature tells you that Corydalis ophiocarpa's blooms aren't very showy. Don't believe everything you read.

Some literature tells you that Corydalis ophiocarpa’s blooms aren’t very showy. Don’t believe everything you read.

Now tiny ones, such as reticulated iris, Siberian squill. glory of the snow (Chionodoxa) and 4-inch dwarf daffodils, have begun poking their heads through the soil.  In the meantime, woolly speedwell (Veronica pectinata) has transformed its evergreen carpet into a mass of blue blossoms.

It’s encouraging to get a preview of the season’s upcoming surprises.

Siberian squill's nodding blooms add a woodland feel to the garden.

Siberian squill’s nodding blooms add a woodland feel to the garden.

 

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Native Shrubs Feed Wildlife, Add Excitement to Garden

I wouldn’t plant rabbitbrush in my yard on a bet.

Yes, I know it’s a Colorado native that attracts wildlife and contributes to biodiversity.  But it’s also uglier than aphids on a rose stem.  And that smell!  There’s a reason rabbitbrush’s botanic name is Chrysothamnus nauseosus.

As far as I’m concerned, rabbitbrush should be relegated to revegetating eroded areas where no one will see or smell it.

Drought-tolerant Pawnee Buttes sand cherry brightens the garden with its white spring flowers and red fall foliage. (Photo courtesy of PlantSelect)

Drought-tolerant Pawnee Buttes sand cherry brightens the garden with its white spring flowers and red fall foliage. (Photo courtesy of PlantSelect)

However, there are beautiful, yet tough native plants that work well in residential landscapes.  Western sand cherry (Prunus besseyi) is one.  Western sand cherry’s cousin, Pawnee Buttes sand cherry (Prunus besseyi ‘Pawnee Buttes’), is even better for those of you who want an 18-inch-high carefree groundcover with multi-season interest. Each April in Denver, small white flowers accent Pawnee Buttes’ lustrous green leaves.  This groundcover’s prolific crop of black cherries then feeds birds in the summer.  When fall rolls around, the plant’s foliage turns bright red.  I’ve planted four Pawnee Buttes in my yard, and am planning to add a fifth.

Other attractive native shrubs that can enhance your landscape while feeding birds include:

Regent serviceberry, a cultivar of Saskatoon serviceberry, displays stunning golden coral foliage each autumn.

Regent serviceberry, a cultivar of Saskatoon serviceberry, displays stunning golden coral foliage each autumn.

  • Saskatoon serviceberry (Amerlanchier alnifolia).  One of my all-time favorites, Saskatoon serviceberry is an airy shrub whose blue berries in June attract birds like crazy.  Those berries taste a lot like regular blueberries and are safe for humans.  In April, serviceberry announces spring with showy white flowers along its stems.  Then the plant leafs out and produces berries.  But fall is my favorite time for this plant because the leaves on my serviceberries (Amerlanchier alnifolia ‘Regent’) turn a remarkable golden coral.  Regent typically grows about six feet tall.
  • Ninebark (Physocarpus opulifolius) features colorful maple-like foliage, flowers, fruit and exfoliating bark.  The plant’s leaves come in a variety of colors, including gold, maroon, wine-red and bronze.  It’s another spring bloomer with spirea-like clusters of white or pink flowers, followed by small clumps of reddish fruit. Ninebark typically grows four to eight feet tall, depending on the variety you select.
  • Red twig dogwood (Cornus sericea).  You may already have several of these growing in your yard.  If you don’t, consider adding them.  Although many sources indicate that these shrubs need medium to wet soil conditions, I’ve found that they tolerate a fair amount of dryness once established.  Their distinguishing feature, of course, is their bright red stems in the winter.  But they also produce tiny white flowers in clusters each spring, followed by white drupes in summer.  Depending on variety, dogwoods may grow from two to eight feet tall.

Except for Pawnee Buttes sand cherry, I planted all of these shrubs in my garden even before I knew they were natives simply because they’re so interesting and low-maintenance.

To learn more about Colorado native plants, visit:

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What You Can do About Emerald Ash Borer

Although emerald ash borer is smaller than a penny, it has already caused millions of dollars in damage to ash trees. (Photo courtesy of Howard Russell, MSU, Bugwood.org)

Although emerald ash borer is smaller than a penny, it has already caused millions of dollars in damage to ash trees. (Photo courtesy of Howard Russell, MSU, Bugwood.org)

When I lived in St. Louis, I had a mature ash tree in my back yard.  It was so beautiful that in the winter, I would sometimes go outside on a moonlit night just to admire the tree’s magnificent form.

I often wonder whether that tree is still standing, now that emerald ash borer (EAB) has spread through 22 states and killed millions of ash trees in less than 12 years.

Since 2002, EAB has been steadily advancing westward from Michigan, culminating most recently in the discovery of the borer in Boulder County, Colorado.  Although EAB wasn’t spotted in that county until September 2013, research indicates that the borers had been at work for three or four years.  According to Colorado State University Extension, it’s anticipated that nearly all of northeastern Colorado will be infested within the next decade.

The city of Boulder alone has 98,000 ash trees; metro Denver has nearly 1.5 million.  You may have several ashes on your block or even in your yard.  So you can imagine the threat that the loss of these trees represents.

If you’re not sure whether your trees are ashes, you can visit the Colorado Department of Agriculture’s EAB page and click the Is your tree an ash tree? link under Additional Resources to see photos and descriptions of ashes.  The EAB page contains an accessible collection of information and resources concerning the emerald ash borer.

What can you do to slow the spread of EAB and handle its consequences?  Here are several suggestions.

  • Don’t transport firewood.  EAB’s flight range is about five miles.  If you carry firewood or other ash materials containing live borers to other locations, you’ll extend EAB’s reach exponentially.  Try to buy firewood where you camp.
  • Keep your ash trees healthy.  This means watering, fertilizing and pruning these plants appropriately.  Colorado State University Extension offers free online tree-care publications, such as Caring for Trees in a Dry Climate.  If your ash trees are healthy, they stand a better chance of absorbing systemic insecticides when treated.
  • Beneath the tree's bark, emerald ash borers create S-shaped tunnels that prevent water and nutrients from flowing throughout the tree. (Photo courtesy of Eric R. Day, VA Polytechnic Institute & State U., Bugwood.org)

    Beneath the tree’s bark, emerald ash borers create S-shaped tunnels that prevent water and nutrients from flowing throughout the tree. (Photo courtesy of Eric R. Day, VA Polytechnic Institute & State U., Bugwood.org)

    Educate yourself about the signs of EAB, which include a thinning canopy, suckering from the tree roots, epicormic branching (weird shoots often sprouting from dormant buds on the trunk), tiny D-shaped exit holes, and S-shaped tunnels under the bark.  Just click the EAB Identification and Reporting link on the EAB page mentioned earlier.  If you suspect that your ash has EAB, contact the Colorado Department of Agriculture by phone at 888-248-5535 or by email at CAPS.program@state.co.us.

  • Monitor EAB’s spread on the EAB page.  If you own ash trees and there’s an infestation within five miles of your neighborhood, you’ll need to decide whether your ashes are worth the money, time and effort involved in EAB control.
  • Explore treatment options.  Colorado State University entomology professor Whitney Cranshaw has developed a helpful publication on control options, including specific insecticides and application procedures, which you’ll also find on the EAB page.
  • Promote tree diversity.  If you plant a variety of tree species on your property, you’ll be less vulnerable to threats to specific tree types, such as ash or Dutch elm.  For a list of suitable trees for the Front Range, click this Colorado Nursery Growers Association link.  Also, be aware that Denver Botanic Gardens and the University of Denver are co-sponsoring a tree diversity conference at the University of Denver on March 7.  For information, visit the University of Denver website.

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Those Innocent-looking Plants Could Be Bad to the Bone

Yellow toadflax and its cousin, Dalmatian toadflax, are both listed as noxious weeds in Colorado. (Photo courtesy of Harlan E. Herbert, Bugwood.org.)

Yellow toadflax and its cousin, Dalmatian toadflax, are both listed as noxious weeds in Colorado. (Photo courtesy of Harlan E. Herbert, Bugwood.org.)

Years ago, a friend gave me several perky yellow perennials that resembled snapdragons.  I promptly planted them in my garden.

Within days, those flowers popped up everywhere.  I realized something was wrong, so I quickly tore out every one of the charmers, and then researched them.

The perennials turned out to be yellow toadflax (Linaria vulgaris), classified as a noxious weed by the Colorado Department of Agriculture.  If I had allowed those plants to continue multiplying, they might have taken over the neighborhood and beyond, crowding out desirable plants and even poisoning livestock.

Beautiful, but nasty.  Myrtle spurge, with its milky sap, can cause blistering on humans, pets and livestock. (Photo courtesy of Kelly Uhing, CO Dept. of Agriculture)

Beautiful, but nasty. Myrtle spurge, with its milky sap, can cause blistering on humans, pets and livestock. (Photo courtesy of Kelly Uhing, CO Dept. of Agriculture)

There are other beautiful noxious weeds that homeowners may unintentionally harbor in their gardens.  Common inhabitants include myrtle spurge (Euphorbia myrsinites), oxeye daisy (Chrysanthemum leucanthemum), salt cedar (Tamarix, which I once admired in my sister’s yard) and Russian olive (Eleagnus angustifolia).

If that weren’t enough, you’ll find popular garden plants showing up on what the state agriculture department calls its “watch list” because they have the potential to become noxious weeds.  Suspects are baby’s breath (Gypsophila paniculata), Japanese bloodgrass (Imperata cylindrical), Scotch broom (Cytisus scoparius), pampas grass (Cortideria jubata) and common bugloss (Anchusa officinalis), to name a few.  For those of you with water gardens, be aware that water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes) are on the watch list, as well.

You’ll find many of these plants in garden centers, as well as online, so it’s a good idea to educate yourself about noxious and near-noxious weeds so you can avoid a situation like the one I had with toadflax.  For a list of plants on the noxious weed and watch lists, visit the Colorado Department of Agriculture website.

And before you go tearing out any myrtle spurge and such, be sure to check the noxious weed fact sheets on the Ag’s website so you’ll know better than to tear out those plants with your bare hands instead of treating them systemically or some other way.  Myrtle spurge contains a poisonous, milky sap that causes blistering.

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Winter Interest Transforms Moonscape Into Wonderland

This young staghorn sumac lends an Old West feel and architectural interest to the winter landscape.

This young staghorn sumac lends an Old West feel and architectural interest to the winter landscape.

If you’ve ever seen a butterfly bush kissed by snow, you appreciate the concept of winter interest.  Snow mutates the shrub’s leaves and faded flowers into a sparkling, lacy delight.

For those of us who live in Colorado and other tundra territories, we need plants with winter interest to prevent our landscapes from resembling moonscapes from December through March, and perhaps longer.

Plants that add a winter-wonderland quality to your environment include those with cold-weather color; architectural form; eye-catching stems and twigs; or fruits, berries, cones and seed heads.

In the winter color category, some refreshing groundcovers are woolly speedwell (Veronica pectinata) and prostrate veronica (Veronica prostrata).  V. pectinata foliage takes on a reddish cast in cold weather, whereas V. prostrata stays green and lush.  Candytuft (Iberis sempervirens) also warms gardeners’ spirits with its deep green winter foliage.  Then there’s Angelina sedum, which turns from its warm-weather yellow-green color to its vibrant winter orange-red hue.

Taller plants that offer color year-round include euonymus (as in Manhattan and moonshadow), lavender, ornamental grasses, Carol Mackie dapne (which retains many of its variegated leaves), Oregon grape holly, yew, pine, fir, spruce and juniper.

Even a blizzard can't dampen the enthusiasm of this maple.

Even a blizzard can’t dampen the enthusiasm of this maple.

As for architectural form, the Kentucky coffee tree often comes to mind.  This drought-tolerant stalwart is beautiful, but you have to decide whether it’s worth the hassle to clean up its brown leathery seed pods.

Other favorites with distinctive form include maple, oak, weeping cherry, dogwood, hawthorn, sumac, willow, Harry Lauder’s walking stick and ornamental grasses.

If you’re looking for attractive bark and stems, consider ornamental cherry trees (with their gleaming red bark), paperbark maple, Kousa dogwood, lacebark elm, mature purple smoketree, red twig dogwood and yellow twig dogwood.

The bright twigs of this young Isanti dogwood contrast sharply with the snow and lend color to the landscape.

The bright twigs of this young Isanti dogwood contrast sharply with the snow and lend color to the landscape.

For plants with berries and such, it’s difficult to beat the winter king hawthorn, with red berries that hang like petite Christmas ornaments from its limbs.  This tough, water-saving plant also thrills gardeners in the spring, with its profuse white flowers and glossy green leaves.

Then there are firethorn (Pyracantha), red chokeberry, Japanese barberry and coral burst crabapple with their attractive fruit.  Meanwhile, Annabelle hydrangea, purple coneflower, yarrow and autumn joy sedum offer eye-catching seed heads, especially in the snow.  Finally, don’t forget roses with showy rosehips, or evergreen trees and shrubs, with their appealing cones.

Besides enlivening your winter garden, plants with showy fruit, berries, cones and seed heads often provide food for wildlife.

If your landscape currently looks moonscape-like, study your plant and seed catalogs to determine what you might plant this spring for a more stimulating winter ambiance in 2014.

For a Canadian blogger’s views on winter interest, visit Gardening for Winter Interest at patinaandcompany.wordpress.com.

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Discover the Cold, Ugly Truth about Sunscald and Frost Cracking

Sunscald discolored the bark on this young nursery tree.  Wrapping the tree in late autumn would likely have prevented injury. (Photo courtesy of Robert Cox)

Sunscald discolored the bark on this young nursery tree. Wrapping the tree in late autumn would likely have prevented injury. (Photo courtesy of Robert Cox)

Now that trees have shed their leaves, you’ll likely notice their architectural splendor.  But you may also notice something else—disfigured trunks from sunscald and frost cracking.

What is sunscald?  “It’s essentially a sunburn, but it’s also got to do with the amount of water and moisture in the trunk,” explains Robert Cox, extension agent—horticulture with Colorado State University in Arapahoe County.  “(Sunscald produces) real obviously discolored bark, particularly on the south or southwest side of a young, non-native, deciduous tree.”

Sunscald-damaged bark may eventually crack or fall off in patches, maiming the tree trunk and leaving it vulnerable to diseases and insects.

Trees prone to sunscald include fruit trees, maples, oaks, ashes, lindens, honey locusts, beeches and willows.

Fortunately, you can reduce the risk of this problem, according to Cox, by protecting your young, deciduous trees that have south, southwestern or western exposure.  Wrap your youngsters with light-colored tree wrap in late fall, and then remove the wrap around mid-April.  Once they’ve grown old enough to produce furrows in their bark, you can then stop wrapping them.

For directions on tree wrapping, visit Colorado State University Extension’s website at www.ext.colostate.edu.

Frost cracking disfigured this stunning maple.  Fortunately, wound wood is forming to cover the damage.

Frost cracking disfigured this stunning maple. Fortunately, wound wood is forming to cover the damage.

As for frost-cracking, here’s how it occurs.  A tree’s bark warms up on a sunny winter or early spring day.  The warmth causes the water in the trunk’s inner bark and in the wood to expand.  As the sun sets, temperatures drop quickly, causing the water to cool and contract. This rapid expansion and contraction can cause vertical cracks in the trunk.

Cox notes that maples, particularly Norway maples, are susceptible to frost cracking.  The only way to prevent frost cracking, he says, is to “plant trees that aren’t prone to frost cracking.  But that’s not really practical,” he points out.  “People are going to plant what they want to plant and deal with the consequences later.”

Trees prone to frost cracking include maples, crabapples, beeches, oaks, lindens, horse chestnuts and willows.

Once a tree has been injured by sunscald or frost cracking, the damage is permanent, though usually not fatal, unless insects or diseases move in and weaken the tree further.

What can you do if your trees fall victim to these two maladies?

“Try to increase its (the tree’s) vigor so that it produces wound wood–that growth you see developing after an injury like that,” explains Cox.  “Fertilize it (the tree) maybe in spring or early summer of the growing season; make sure it gets sufficient water; keep it watered during dry spells in the winter—anything you can do to keep it healthy so it does form that wound wood readily.”

Concerning trunk cracks, he adds, “Certainly, use of a fungicide wouldn’t be a bad idea.  It isn’t going to hurt anything to spray a liquid fungicide in that frost crack periodically just to make sure things don’t happen in there, because water’s going to get in there, snow’s going to melt and rain’s going to come into that wound.”

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Serendipity Surfaces in the Shade

My grand gardening scheme consisted of creating a woodland look with Rozanne cranesbill and dogwoods in my part-shade front yard.  But Mother Nature just had to put her two cents in and produce a stand of Corydalis ophiocarpa to mingle with the cranesbill.

You see, about five years ago I planted a few corydalises in my side yard.  They reseeded aggressively and tended to move around.  Eventually they disappeared from my side yard because I didn’t water them enough.

But their seeds sneaked into my front yard, presumably because I’m always moving soil from place to place.  This resulted in said mingling of corydalis and cranesbill with cranesbill blossoms peeking out from corydalis’ fern-like foliage.

A Rozanne cranesbill blossom peeks from beneath the fronds of the low-maintenance perennial, Corydalis ophiocarpa.

A Rozanne cranesbill blossom peeks from beneath the fronds of the low-maintenance perennial, Corydalis ophiocarpa.

I love it!  It’s exactly the low-maintenance woodland feel I was looking for.  It’s also a perfect complement to my Isanti red twig dogwoods that emerge from the middle of the groundcovers. As long as I keep the soil from drying out completely, my woodland should stay intact and hopefully spread along my foundation.

Corydalis lutea offers fern-like foliage with bright yellow blooms from May through September in Colorado. (Photo courtesy of robsplants.com.)

Corydalis lutea offers fern-like foliage with bright yellow blooms from May through September in Colorado. (Photo courtesy of robsplants.com.)

Ferns, other than ostrich fern (Matteuccia struthiopteris) can be difficult to grow in Colorado because of the dry climate.  Perennial corydalis fills the void.  You can plant Corydalis ophiocarpa or its cousin, Corydalis lutea.  Both are great-looking plants.  C. lutea blooms longer, cut I prefer the leaf structure of C. ophiocarpa.  It’s a personal thing.

Other outstanding shade-tolerant perennials include bleeding heart (Dicentra spectabilis or the shorter, fluffier D. formosa), tall garden phlox (Phlox paniculata), moonshadow winter creeper (Euonymus fortunei ‘Moonshadow’), variegated Solomon’s seal (Polygonatum odoratum ‘Variegatum’), oxeye sunflowers (Heliopsis helianthoides), plumbago (Ceratostigma plumbaginoides) and even prairie winecups (Callirhoe involucrata—yes, it will bloom in part shade).

As for shrubs and trees, excellent choices for part shade are golden spirit smokebush (Cotinus coggygria ‘Ancot’), autumn brilliance serviceberry (Amelanchier x grandiflora ‘Autumn Brilliance’), dart’s gold and Diabolo® ninebark (Physocarpus opulifolius ‘Dart’s Gold’ and P. opulifolius ‘Diabolo’), oakleaf hydrangea (Hydrangea quercifolia), Knockout™ shrub rose (Rosa ‘Radrazz’ Knockout), and yews (Taxus spp.).

As you can see from these lists of plants, shade gardening can be downright exciting.  And you never know what Mother Nature might contribute to your efforts.

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