Plant Spotlight 2002

Cotinus coggygria (coh-TINE-us co-gig-reah)
Common name: Eurasian Smokebush

The first time I can remember being enough of a gardener to notice a distinctly different – looking shrub in a garden setting, it turned out to be Cotinus coggygria 'Royal Purple.' Here this thing sat amidst perennials in a friend's garden, four feet tall, with small, oval, PURPLE leaves possessed of a dull, leathery sheen. Young growth at the tips was shinier and more of a blood red-yowzer. Years later I still find it one of the most arresting shrubs available to northern gardeners today.

There are many varieties of Smokebush with which to play. 'Royal Purple' is common in the trade and in my mind it's the most striking of the genus. The wispy clumps of tiny, smoke-like flowers are a purplish-pink. 'Velvet Cloak' is virtually identical to 'RP', 'Nordine' has more reddish leaves and pink flowers, and 'Daydream' has green leaves with tan, very smoke-like flowers.

Smokebush is not super-hardy (-20° F/-29° C), though it is correctly sold as a Zone 4 plant. Some dieback is common as the result of colder winters, but it grows back quickly in the spring, and should discourage none from growing this marvelous plant.

Care and Use
Smokebush needs full sun; good light is essential for rich foliage coloration. The same old rules of soil apply: well-drained soil with ample organic matter. Avoid spots that remain damp. Left alone in the right spot in warmer climes, Smokebushes will grow 10' high and equally as wide. Winter dieback keeps them considerably smaller than that, plus you can prune as harshly as you choose to control height and width.

The plant flowers on new growth. Some people cut the shrub all the way to the ground in early spring, because foliage on new growth will have richer color. What I'm trying to say is it's easy to grow the shrub anywhere between 2' to 4' tall, and however wide or narrow you choose.

Fertilize in spring with 10-10-10 if your soil needs help. Put down a 2" layer of mulch after ground warms in the spring. Don't let the soil dry out around the plant during the growing season, particularly during the heat of the summer. This is a shrub you want to remember to water once a week. Stop watering in mid-September to help the plant into winter dormancy. If late fall is very dry and temperatures remain above freezing, give the ground a good soak after the plant has gone dormant. This is called gardening.

Plant smokebush in your perennial gardens. Good perennials to bounce off the front of it are Alchemilla mollis (Lady's Mantle), taller Stachys. Irises, and Artemisias. Surround it with large- or long-leaved perennials such as Digitalis, Lilies, Monarda, or something airy like Perovskia (Russian Sage).

In a mixed-shrub planting, the authors of Growing Shrubs and Small Trees in Cold Climates (look for this book in an upcoming Top Pick) suggest Buring Bush, hydrangeas (I wouldn't, but I see what they mean), and Mock Orange for starters. To this list I would add evergreens such as junipers, arborvitae, and Mugho pine.

Polygonatum (puh-lig-oh-NATE-um)
Common name: Soloman's Seal

How about an easy to grow, quick to expand, living sculpture of a plant that thrives in shade? It's Soloman's Seal, and I never tire of it.

Pictured is P. falcatum 'Variegatum,' the darling of the spring shade garden. It flowers white quite early in May, charming little bells that hang down like mini-chandeliers. These will be followed by blue-black berries; the leaves take on a golden-yellow hue in the fall.

I can't imagine how disappointed I'd be if my vast areas of shade didn't have this plant gracefully holding forth everywhere I need a little extra movement and intrigue. There are many varieties to choose from, including a dwarf (P. humile) and a large variety that tops out above three feet (P. biflorum).

Care and Use
Soloman's Seal is a woodland plant, and as such prefers well-draining soil amended with ample organic matter. It will handle some sun and does surprisingly well in dry soil conditions, but is not something to ignore during periods of drought. The thing to remember is that the plant arcs, it leaps out from the base, so allow it to do so over more finely textured plants. It also looks great in the front of the border.

Expands quickly without being invasive. Divides without a fuss. Many varieties hardy to Zone 3.

Nepeta (NEP-e-tuh)
Common name: Catnip

Airy and graceful, catmints bring such a refined touch of elegance to the landscape that one would think they must have some hidden drawback – you know, hard to grow, invasive as quack grass, favored by deer – but no! Catmints are easy to grow, know their bounds, and are on everyone's list of deer-proof perennials.

Plus they work well in a wide variety of places. They look great busting up the front of the border, stand out in the middle of the bed, and the taller varieties hold their own at the back. I particularly like catmint tumbling out from the front into pathways.

Foliage is a major reason to experiment with this perennial. Leaves, depending on variety, are a pubescent silvery-gray. Coupled with the tiny twists of tubular flowers, a mint-like aroma, and four-sided stems, catmints are a distinctive addition to the northern garden.

Nepeta sibirica 'Souvenir d’Andre Chaudron' syn 'Blue Beauty'

There are half a dozen varieties commonly found in the northern trade. Most popular are 'Blue Wonder,' which reveals rich lavender-blue flowers for a relatively long period of time (up to five weeks) in mid-season. It grows between 12 to 14 inches tall and will rebloom if sheared. N. sibirica 'Souvenir d'Andre Chaudron' is the current favorite in the Twin Cities, and deservedly so. It grows quite vertically up to 3' tall and blooms profusely. N. subsessilis is a Japanese species that looks like a shorter version of 'Chaudron.' Also reblooms when sheared.

'Six Hills Giant' is the tallest variety, turning into a 3' x 3' shrub-like bush by season's end. Blooms lavender-blue for a month or more mid-season. Won't rebloom when sheared, but it looks neater for the rest of the season.

Care and Use
Catmints prefer full sun but are worthwhile in areas where they will receive at least four hours of direct, midday sun. Organic content of soil is not as important as that the soil be well drained. Fertilize twice per season (mid-May and the end of June) for maximum fullness and bloom. Shear the plants after first flowering for appearance and, in some cases, rebloom.

Once established they do become fairly drought-tolerant. All hardy to Zone 4, 'Six Hills Giant' reliably to Zone 3.

Pulmonaria spp. (puhl-mun-AIR-ee-uh)
Common Name: Lungwort

Pulmonaria longifolia 'E.B. Anderson'.

A few of these are already in bloom in Zone 4, with Zones 3 and 2 to follow. That's right, here we have a large class of perennials hardy to minus forty Fahrenheit (Saskatoon, for my Canadian visitors).

Lungworts are a semi-shade plant that I could envision surpassing hosta in popularity given more promotion. Whereas most of the lip-smacking surrounds their wonderfully diverse, speckled, mottled, and streaked foliage, their floral display is certainly something to sniff at.

Lungworts are low-growing plants with a beefy, fibrous root system that allows the plant to clump out quite quickly, without being invasive. 'Milky Way' is a recent introduction featuring rich, silver-spotted leaves and blood red flowers. Pulmonaria longifolia sports several varieties known for their narrower leaves. Most of the pink-blooming varieties are Pulmonaria angustifolia, and you will find several varieties of the species at your nursery.

Care and Use

Imagine lungworts to be smallish hosta with irregular spots instead of stripes. Except they'll tolerate more direct sun. They are wonderful as single specimens mixed in with hosta, astilbe, lamium, asarum, aquilegia, polemonium, heuchera, polygonatum, ferns, and all the usual semi-shade suspects. Very useful as an all-purpose groundcover. In the garden bed, place them near the front where they can be readily seen.

They are easy to divide (divide in spring right after blooming) and hardy as granite. Can be grown in full sun in areas where they are not allowed to dry out. All lungworts bloom in the spring, and don't give much re-bloom when deadheaded. Still, deadheading is a good idea for the sake of appearance. Later in the season, if foliage is ragged, you can remove older leaves to spark fresh basil growth.

Lamium maculatum (LAY-me-um mack-you-LAY-tum)
Common Name: Spotted Dead Nettle

I know I've said this before, but this time I'm serious: I cannot imagine gardening without lamium.

This shade groundcover is unmatched in its ability to liven up a shady area. Foliage is the key here; lamium adds instant pizzazz.

In the north, cultivars to look for include 'Pink Pewter,' which features silver leaves with thin green margins and bountiful pink blooms; 'White Nancy,' much the same look as PP but clean white blooms; 'Orchid Frost,' a newer cultivar with silver centers within blue-green foliage. I grow an older, pink-blooming variety with name unknown to me, in addition to Nancy.

Foliage gets very dense as it hugs the ground, rarely rising up more than ten inches, and often trailing outward just above the soil. It gets thick enough that it blocks out weeds. This is a spring bloomer that surprises the garden with waves of bloom here and there through the entire season.

Care and Use

Pink Pewter shoulders its way through Geranium, Polygonatum, and Vinca

You need to loosen and lighten the soil before planting. Making sure the soil contains a good amount of organic matter is helpful in getting lamium to take hold, although once established it wanders freely (without being invasive) and seems to do well in any type of soil.

Lamium grows in everything from full shade to part sun, but flourishes in the dappled-shade, woodland environment.

It must reseed freely. I never fertilize it, it's impractical to deadhead, yet each year I'll find new little bits over here, and a cute tuft I know I didn't plant over there. You can dig it up any time of year and move it; divide by chopping out chunks with a sharp shovel.

Buy it in flats if possible, or get enough pots of the stuff where you can plant it throughout the shady parts of your yard and garden. Water it in well and don't let it dry out the first to second year. Lamium has a shallow root system. Surprisingly, once established, it tolerates dry soils very well. If it sneaks out into part or full sun, it'll keep going so long as you keep it moist in sunny, hot locations.

I mix it with everything. Under trees, a bench, weaving past hosta, along a pathway or anywhere you want a dollop of magic. And it's very fashionable right now to use it as a trailer in containers. Leaves and habit like lamium, you can't put it in the wrong place.

Physocarpus (feye-so-CAR-pus)
Common Name: Ninebark

Very hardy and native to cold climates, Ninebark is a shrub finally getting its due from the nursery industry. I can't think of a design I've created in the last two years in which I haven't include one, or five.

My favorite is Physocarpus opulifolius 'Diabolo,' with its rich brown-bronze foliage and umbels of tiny, pinkish-white flowers in early summer. Tops off at eight feet, with a solid six-foot width. All Ninebarks mature to become dense shrubs, good for screening or informal hedges, and are wonderful in naturalized settings.

Other good varieties: 'Dart's Gold' gives you a pale-green-to-gold leaf to work with, in a slightly smaller (six-foot high and wide) form. 'Nanus' features rich green foliage, and if makes an excellent clipped or informal, mid-sized hedge.

Care and Use
Ninebarks need full sun and will do fine in windy, exposed areas. They are not picky about soil type, but as always, will do best in soil that has been lightened with organic matter, though you don't need to go crazy about it. If the soil drains pretty well, you're in good shape. "Will it grow in heavy clay?," I am so frequently asked. Standard answer, of course not.

Water once a week after planting, but once you witness healthy new growth, you can down the watering to twice a month in periods of no rain. Once established, Ninebarks prefer it on the dry side, so wait to water until the top two inches of soil under the mulch have dried out. Fertilize once each spring with granular 10-10-10 fertilizer.

As is the case with any tree or shrub, mulching with four-inches of shredded bark after plantings is recommended.

Hardy to Zone 2 (-50 degrees Fahrenheit).

Lilium (lily-um)
Common Name: Lily

The Renegade Gardener was once involved with a delightful and charming woman he thought very possibly could be the one. She read good books, loved all types of music, hated Hollywood movies, preferred her Thai food hot and her beer cold. Best of all, she was hopelessly addicted to gardening. It was one of those relationships that went from zero to sixty in about four days.

Then one day during the summer she and the Renegade were talking about garden design when she mentioned that she didn't like lilies. Said it just like that, "I don't like lilies. Don't like the way they look." Thinking back on it today, the Renegade Gardener realizes he can't even recall her name.

You have to love lilies! Their use is basically required in the herbaceous border. There are hundreds to choose from, in a variety of categories, and whereas there is a notion in some circles that they can be difficult to grow, the opposite is true. Growing lilies is easy.

Lilies are bulbs plants, and though I've covered this before, it bears repeating: daylilies are not lilies. Lilies are the genus Lilium, while daylilies are genus Hemerocallis, and are in no way related.

Lilies do come with a certain amount of detail to digest. They are divided into different types in the following manner:

Division I Asiatic Hybrids (Examples: Connecticut King, Enchantment, Chianti)
Division II Martagon Hybrids Examples: Claude Shride, Terrace City, City Lights)
Division VI Trumpet and Aurelian Hybrids (Examples: Easter Lily, Pink Perfection)
Division VII Oriental Hybrids (Examples: Stargazer, Casa Blanca)
Division VIII Complex Interdivisional Hybrids (Examples: Orienpets (Oriental/Trumpet) and LA Hybrids
Dvision IX Species Lilies – Wild lilies from which the hybrids originated

Don't ask me what happened to Divisions III, IV, V or IX. Perhaps they have been reserved for future use by the next generation of plant hybridizers with way too much time on their hands. But don't worry too much about the divisions. In a nutshell, this is all you need to remember:

Asiatic Lily (1A)

Asiatic lilies are derived from varieties native to Asia, and tend to be the easiest to grow. They are the most hardy (to Zone 2 with heavy winter mulching) and feature a wide variety of colors: white, red, yellow, orange, pink, even green. Most multiply rapidly and bloom over a long period from late June through July, with a few around as late as August. They like a nice sunny spot, at least five hours or more for prolific blooms.

Asiatic lilies range from two to three, maybe four feet in height, with large blooms to 5" or more. They are divided into three groups based upon the orientation of the flower:

  1A — Upfacing
  1B — Outfacing
  1C — Downfacing (Pendant)

This will help you when you begin choosing Asiatics from fancy-schmancy catalogs. If the code given for the bulb is "1C," that means it is an Asiatic (Division I) with a downfacing bloom.

Martagon lilies are hybrids from wild varieties scattered from Europe to Siberia to Mongolia. Their chief asset is that they are a woodland plant, and do best in light shade. Mine get morning sun then afternoon shade, and they thrive. They are slower to multiply than Asiatics, and can go many years without need for division. They grow tall, four feet or better, and can carry up to 50 flowers on a single stem. Flowers are always pendant.

Martagon Lilies

Colors run the gamut, but also include creams, browns, dark purples, spotted and mottled. They are spring bloomers, April to May. Also known as Turk's Cap Lilies. Reliable hardiness to Zone 3, and again, winter mulch after ground freeze is advised.

Trumpet and Aurelian Hybrids are heavily perfumed with large blooms, growing very tall (4' to 6'), which is why they are so spectacular. Many have the classic Easter Lily form.

Trumpet colors range from white to yellow, gold, pink, purple, apricot, maroon, and every combination in between. Varieties bloom from mid-season to September. They are not as reliably hardy in the north, but merit experimentation and use.

Oriental Lilies

Oriental Hybrids come from wild varieties principally found in Japan and Korea. They are perhaps the most exotic in bloom, with flowers up to 10" across, though they rarely pass 3' in height. Smaller varieties are great in containers; pot in the fall, then place the container in the ground and mulch after ground freeze. Bring container back up and out in the spring, and the bulb will begin growing.

Colors available in the north include white, pink and red (often with gold highlights) and spotted. Orientals are not the easiest to grow in the north, however, due principally to the fact that they bloom late (August into September) and thus mature late. Cold falls and early winters just don't give them enough time to regenerate. They also have a harder time adapting to very hot summers. They also prefer acidic soil, more so than the other types, with a pH as low as 5.0. Work with the other lilies first, then give Orientals a try after you've had success.

Care and Use
With lilies, the important thing is to get the soil right. Lilies need well-drained soil with a slightly acidic pH (Orientals lower, to 5.0) So you want do dig a hole at least 10" deep and fill it with a mixture of good black dirt, organic matter (say 20% – 35%) and sharp sand, for drainage. If unsure about pH, get your mixture tested.

Plant the bulbs 4" to 6" deep in the fall/early winter; they are not very fussy about this. Go at least 6" deep in Zones 2 and 3, and with big bulbs, try them at 7" deep. Like all bulbs, they prefer it dry after blooming. Space the bulbs at least 6" apart. Do not fertilize. Fall is the accepted time to plant, and means the lilies will bloom when the books and catalogs say they will. But you can also plant lilies in the spring – they'll bloom that season, though later than normal.

When the plants emerge, hit them with a balanced granular fertilizer, and repeat the application a month later. Don't use a fertilizer with too much nitrogen. As the blooms fade, cut off the stems below the blooms and above the first set of leaves. At this time you can fertilize again, if soil is poor quality. Allow the stem and leaves to remain upright, don't cut it down. I generally leave my stems alone until they are completely brown, the leaves withered.

It's a matter of taste, but I don't like too many lilies in one clump. The better gardens I view always seem to have a striking lily or two here, a lily stem or three over there. Great waves of them just don't seem as pretty as using lilies as more singular accents. Better gardeners dig up their lily bulbs and divide them every few years or so, so that their lilies remain lean and mean.

Tsuga canadensis (SOO-guh can-uh-den-sis)
Common Name: Canadian or Eastern Hemlock

This year I've fallen in love with hemlocks. Didn't think that much about them, don't see them much, then I stumbled upon rows of them at Bachman's Wholesale nursery in Farmington and thought, man, what's the catch?

Tsuga canadensis

Turns out there isn't one. The original Tsuga canadensis is the largest of the five varieties available to northern gardeners, and listen to Michael Dirr describe it in his Bible, Dirr's Hardy Trees and Shrubs: "What a grand needle evergreen – softly pyramidal in outline, deep green needles, good tolerance of shade or sun, and many landscape uses. I have never met a specimen I did not appreciate."

Canadian Hemlock will grow to 70' with a spread of 35', so for smaller areas look at the weeping variety 'Sargentii,' which grows into a willowy, cavernous, 15'-high by 30'-wide tumbling waterfall of texture. The one I've been planting in people's yards most often, however, is Tsuga canadensis 'Monler' (sometimes sold as 'Emerald Fountain'), a more dense, formal, columnar variety that tops out at 10' while retaining a 3' width. Gorgeous, gorgeous plant, good around the foundation or out adding fun (and winter interest) to the perennial bed. I grimace when I think of the times I've sold a client a Holmstrup arborvitae, instead of 'Monler.' Ugh.

Other varieties include the ground-hugging 'Cole's Prostrate,' hovering only 2' above ground while sprawling out 5', and 'Pendula,' a weeping form maturing at 15'.

Care and Uses
All varieties do well in sun to part shade, but generally prefer less than full sun. 'Monler' handles full sun best. They prefer moist, well-drained soil with a pH between 5.5 to 6.5. In the north they are virtually disease-free, but are being plagued by attacks of the wooly adelgid on the East Coast. All respond well to shearing, though you would probably only shear 'Monler,' if for some reason you wanted it very dense and formal in appearance.

Place hemlocks where they can be seen up close. The undersides of the needles, quite often visible, feature two silver stripes. If landscaping along a fence, use 'Pendula' alone as a sculptural focal point. 'Monler' looks great solo but also makes a fine hedge. 'Coles Prostrate' is a great groundcover, preferring at least part shade, and looks great on slopes and near rocky ponds and streams.

All varieties hardy to Zone 3.

Euphorbia (you-FOR-bee-uh)
Common Name: Spurge

Ran across some E. polychroma (Cushion Spurge) starting its fall turn into a blazing, reddish dazzler, and couldn't figure out why I hadn't written up this genus prior. There are many, many spurge varieties native to most parts of the world, and luckily, a few of the nicest varieties have proven to be hardy in the north.

Varieties of Euphorbia are not usually on our list as we wade through our early years of gardening. Flowers are rather insignificant, so you think, what's the point? But it is at that point when we figure out that foliage, not flowers, is the key to a beautiful garden, that spurge becomes essential.

You grow it for the fabulous form and foliage, plus eye-catching bracts (brightly colored leaves that resemble flowers). Long-lived when grown in light, well-drained soil, Euphorbia is guaranteed to delight.

E. corollata is a delicate native blooming in white as it reaches three feet in height, and is often used after killing off your third attempt at Baby's Breath (Gypsophila).

E. polychroma is the most common to the northern trade, makes the most impact, and is a good place to start. Reaches 18" to 24" in height, yellow bracts offset perfectly by creamy pale-green leaves.

E. griffithii is now proven hardy to Zone 4 and will be seen more often in the trade. Similar in form but twice as tall as E. corollata, it sports red-veined leaves and blazing orange bracts.

Care and Use

Spurges prefer full sun but will perform admirably in lightest shade. They like light soil (sandy loam is perfect) and will die by June in clay/heavy soils. Figure average moisture requirements, though after a year or two they tolerate dry spells. Divide in early spring after three to four years; a woody, central crown will develop and the plant will appear to be dying out in the center, which it is.

But be careful. You'll want to completely wash all soil from the root system after taking the plant up, then cut the thick, fleshy roots with a sharp knife, ensuring that each division has several eyes and ample roots.

I'm done telling people where to plant plants and in conjunction with what other plants. That's for you to figure out, so you develop as a gardener. All varieties listed are hardy to Zone 4, but also worth a try in Zone 3, providing good soil, fertilizer a few times a season, and winter mulch.

Euonymus alatus 'Compactus' (you-JUAN-uh-mus uh-LAH-tus)
Common Name: Dwarf Winged Euonymus, Dwarf Burning Bush

Summer color
Fall color

One of the absolute best medium-size shrubs for residential landscape use, dwarf burning bush is currently out-sparkling just about everything in the late fall, northern landscape. They don't call it burning bush (and it didn't capture Moses's attention) for nothing.

'Compactus' is, as the name implies, a more compact, denser variety of E. alatus than the classic winged euonymus. It grows quickly to eight to ten feet in height with a natural width of six to eight feet. Somewhat shorter in shade. Width is easily controlled by base pruning. Corky branch texture is intriguing. Relatively small, attractive leaves of a soothing light green provide great summer interest, as the does the dense, vertical-to-horizontal branching habit. 'Compactus' always looks like a plant in motion.

But it is the blazing, pinkish-red fall color (when the plant is grown in at least five hours of direct, midday sun) that makes this shrub such a treat.

Care and Use

'Compactus' is easy to grow and quite disease/pest resistant. It's an excellent specimen plant, meaning you should place it where all or most of the plant is visible in the garden. It tolerates a wide range of soil types, and will grow in everything except the dampest soils.

It will do fine in medium shade, but as mentioned above, good daytime sun is needed if you want to see fireworks in the fall. Whether planted near the foundation of the house, or further out in the landscape, it will soon become one of your favorite deciduous shrubs.

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