What’s My Zone?

Gardeners and attentive news followers may know by now that the USDA has just released an update of the Plant Hardiness Zone Map, and to nobody’s surprise, New Hampshire is getting warmer, with the current “winter” adding to the accumulating evidence.

Hardiness zones are typically used to determine which plants will grow in a given area, and are displayed on the map of North America as broad colorful strokes depicting the average lowest temperature likely to be experienced each winter. Each zone is given a number, with lower digits representing colder regions, and vice versa, and the zones are in 10 degree F. increments. Each is further broken down into subranges “a” or “b” – thus, “USDA Zone 5” indicates average minimum winter temps of -10 to -20 degrees F; “5a” is -20 to -15, and “5b” being -15 to -10 degrees F. In the warmest parts of the U.S., it’s not the cold that is a limiting factor: it’s the heat, and heat zone maps have been created for those areas that will never experience a snowflake, or black ice.

The last version of the Plant Hardiness Zone Map was issued in 1990, and was based upon 12 years of meteorological data. Creators of the 2012 map were able to use the latest in computing technology to compile 30 years of readings from more measurement sites into an interactive tool that is much more detailed. When compared to the 1990 map, it is clear that warmer zones have been creeping northward, and that is also true in New Hampshire. However, some of the changes can be attributed to the additional data and computational ability, and the USDA makes no claims about the influence of planetary warming leading to climate change.


Gardeners can be a quirky bunch, often conversing in botanical Latin and using the Zone Map as part of their identity, as in, “I’m a solid Zone 5b” (meaning average minimum temperatures of -10 to -15 degrees F.) Importantly, these temperature ranges refer to ambient air and not to wind chill temperatures, which only apply to exposed human skin. I am often asked to offer plant recommendations for “my Zone 4a (-25 to -30 degrees F.) garden in Amherst”, or some other southern New Hampshire location. In fact, most of the lower half of the state lies in Zone 5a or 5b, with the extreme southeasterly portion enjoying Zone 6 (0 to -10 degrees F.) winters. That the Seacoast is milder is unsurprising, but the new map shows large scattered blocks of western New Hampshire, from south of Keene to north of New London as also being in Zone 6a. This should come as welcome news to gardeners in those areas, with a larger palette of plants they can now try.

Gardening books, plant tags and catalogs typically provide the hardiness range of a given plant, assisting the reader when deciding whether she can grow it. However, these zones, while extremely helpful, are more of a guide than a rule – there are other factors which come into play: winter sun exposure (although counterintuitive, less winter sun, especially in the afternoon, is often better for some evergreens), the amount of snow cover (more is usually better, as snow is an insulator,) plant vigor, and the microclimate – or the immediate vicinity of the plant’s intended location – is it sheltered? Does it retain the sun’s warmth into the evening? And lastly, how wet the soil is in winter – plants that do quite well in a cold yet arid climate for instance, the high desert – often perish in our icy mud.

Part of the fun in gardening is pushing the limits of what plants can be grown successfully. Northern gardeners are eager to try more tender species, while those in the south – especially snowbirds, may attempt plants that require more cold to survive. Despite our typically cold winters, we in central New England can grow an astonishing variety of plants, but our warm and humid summers often prevent success with those species happier in the more temperate climes of England or maritime Canada. Which means that we are far more likely to succeed with growing ornamental bananas and gingers rather than the holy grail of many local gardeners: stunningly perfect spires of 6-foot tall delphiniums.

Not that the bananas and gingers will make it through our winters, at least according to the new hardiness zone map.

Selecting and Caring for Clematis

Clematis are lovely and useful plants for the garden. We offer 3 different types: the familiar twining vines, and the lesser-known shrubby and trailing forms.

• The vines are available as the popular large-flowered hybrids as well as small-flowered hybrids and species. They are typically planted to grow up a lamppost or trellis, but are also attractive when allowed to clamber up a tree or shrub.


• Shrubby clematis are commonly used in the perennial garden, where they offer late-season color. Most have a rather lazy habit, and can be supported using neighboring plants or stakes and twine.


• Trailing clematis are the least known, and are typically either tied to a support such as a mailbox or a lamppost, or given the chance to trail freely through a garden.

Clematis are generally easy to grow, providing that certain conditions are met. First, they usually require at least 1/2 day of sun. Afternoon shade will benefit the blossoms of many clematis, especially those with prominent contrasting “bars” in the flowers. A deep, fertile soil is also needed, which can be prepared by digging a hole at least the size of a 5-gallon bucket, and discarding any poor soil. To the better soil, add an equal quantity of organic matter, such as Coast of Maine™ compost. One-half cup or so each of ground limestone and an organic fertilizer such as Pro-Gro™ is also beneficial. Blend all the ingredients, dump the amended soil back into the hole, and plant the clematis carefully, taking care not to damage brittle stems when securing to a trellis or other support. Good mulch helps to keep the soil cool and moist. Water well, and maintain it as you would any new planting.

Large-flowered clematis are susceptible to a disease known as Clematis Wilt. This disease remains a mystery to gardeners and scientists alike, for it is unknown if it is caused by a fungus, wounding of the stems caused by windy conditions or mishandling, or a phenomenon of the plant being unable to provide enough water to the stems during stressful weather. In any event, it is characterized by a sudden wilting of the leaves starting at the tips of the stems, and progressing downward. Benomyl™, a commercial fungicide, is commonly used to counteract it. Pruning the stems down to healthy growth will often stop the disease, and new stems will usually arise from buds hidden below ground. Clematis Wilt rarely, if ever, will kill clematis; at most flowering may be disappointingly delayed. Please note that The Mixed Border Nursery will not replace any clematis that has been affected by Clematis Wilt.

Pruning clematis is often confusing to the uninitiated. However, once you understand that you will not kill clematis either by pruning it according to the wrong method, or by not pruning it at all, it becomes much easier. Clematis are grouped according to the way they flower, and this governs how they ought to be pruned. If you are unsure what type you have in your garden, observe its flowering habits for a season, and follow the recommendations that most closely match what you have. Except for Group 1 types, all may be cut back severely in spring with at worst a temporary effect on flowering.

Group 1:
These plants flower early on old stems and generally do not need to be pruned, except to remove dead or damaged stems. If pruning is necessary to control growth, cut stems back after flowering.

Examples:
Clematis alpina and varieties
” macrophylla and varieties

Group 2:
These also flower on old wood, but a later flush of flowers happens in late summer on new growth. In early spring before buds have opened, prune out any dead or weak stems, and cut back remaining stems to a pair of buds. The lower down the stems you cut, the more flowering will be delayed. Cutting the stems by half is a good rule of thumb.

Examples:

Clematis ‘Arctic Queen’	C. ‘Asao’	C. ‘Belle of Woking’
C. ‘Blue Ravine’
C. ‘Carnaby’	C. ‘Crystal Fountain’	C. ‘Duchess of Edinbrough’
C. ‘Elsa Spath’	C. ‘Empress’	C. ‘Franziska Maria’
C. ‘Guernsey Cream’	C. ‘Henryi’	C. ‘Isago’
C. ‘Josephine’	C. lanuginosa ‘Candida’	C. ‘Nelly Moser’
C. ‘Niobe’***	C. ‘Perrin’s Pride’	C. ‘Piilu’
C. ‘Proteus’	C. ‘Rebecca’	C. ‘Rhapsody’***
C. ‘Silver Moon’	C. ‘Sprinkles’	C. ‘Sunset’***
C. ‘Tie Dye’	C. ‘Rosemoor’	C. ‘Sugar Candy’
C. ‘Veronica’s Choice’	C. Ville de Lyon’***	C. ‘Vino’
C. ‘Vyvyan Pennell’	C. ‘Warsaw Nike’	C. ‘Will Goodwin’

Group 3:
Flowers are produced on new stems each year, so vines can be cut down to a pair of buds near the ground in late winter or early spring.

Examples:

Clematis ‘Aljonushka’	C. ‘Arabella’	C. ‘Barbara Harrington’
C. ‘Comtesse de Bouchard’	C. ‘Hagley Hybrid’	C. heracleifolia and hybrids: ‘Mrs. Robert Brydon’
C. integrifolia and hybrids	C. ‘Jackmannii Superba’	C. ‘Niobe’***
C. ‘Perle D’Azur’	C. ‘Petite FauÇon’	C. recta and varieties
C. ‘Rhapsody’***	C. ‘Rouge Cardinal’	C. tangutica and varieties
C. terniflora (a.k.a. C. paniculata)	C. texensis ‘Duchess of Albany’,‘Odoriba’, ‘Pagoda’	C. Ville de Lyon’***
C. viticella and hybrids:
C. v. ‘Mrs. Betty Corning’	C. v. ‘Etoile Violette’	C. v. ‘Kermesina’
C. v. ‘Polish Spirit’	C. v. ‘Purpurea Plena Elegans’

***Note: these varieties may be pruned according to either Group 2 or Group 3.

Photos courtesy of Donahues Clematis

Hazels and Hellebores – the Flowers of Early Spring

Winter can seem interminable to the New England gardener, with the possibility of snow from October to April. By March, we are desperate to see the inky brushstrokes of branches against the white sheet of snow become transformed into the verdant watercolor that is spring. We long for green. We long for flowers.


Hamamelis intermedia 'Pallida'

For those who think that Forsythias and crocuses are the floral harbingers of spring, they are late to the party. Witch Hazels (Hamamelis) have been blooming in our gardens since the end of February, and will continue for weeks to come. They are the earliest woody plants to bloom where they are hardy (USDA Zone 5). Although of exotic origin, they are related to our native Witch Hazel (Hamamelis virginiana), which unfurls its pale yellow ribbon-like petals in October and November.

The spring-bloomers are ornamentally superior to the native Witch Hazel. Their flowers are far showier, and hybridization has resulted in colors ranging from soft yellow to brassier tones, and even orangey-reds. Most are fragrant, adding to their charm, and an armload of branches brought into the house will scent the air with sweetness. The variety ‘Arnold’s Promise’ has long been my favorite, with its bright lemony-yellow blossoms.


Hamamelis intermedia 'Pallida' flowering with snow still on the ground

Whether in bloom or in size, these are not timid shrubs. They’ll flower dependably, beginning in late February or early March, even in the snow. Each year they’ll grow larger, eventually reaching twenty feet or more in height, with a wide spread. I think they are excellent choices for a sunny corner of the house, or at the edge of a woodland garden, as Witch Hazels can tolerate a little shade. Plant some Snowdrop bulbs (Galanthus) beneath one in the fall, and you will be rewarded with your own flower show each year.


Corylopsis spicata 'Golden Spring' in bloom

Forsythias can be troublesome shrubs, as they often grow ungainly without proper pruning. A better choice might be Winter Hazel (Corylopsis spicata), which as I write this in late March, is just coming into bloom. The flowers are a lovely shade of soft yellow, and are carried on stems that are much more elegant than the common Forsythia. Although reported to be hardy only to Zone 6, we have been growing Winter Hazel in our Zone 5 gardens for the past 20 years with little or no winter damage. The pleated, bluish-green leaves remain attractive all season. We have a chartreuse-foliaged one planted in our garden (C. spicata ‘Golden Spring’,) and hope to offer this variety for sale soon. All benefit from a little shade, especially in the afternoon.


Hellebore hybrid

Lenten Rose, or Hellebore (Helleborus), have long been appreciated in Europe for their early blooms that defy cold weather. Over recent years, they have gained a following in the US, and there has been much breeding work done to produce a virtual rainbow of colors and “doubled” flowers. Our Hellebores started to emerge from the ground once the snow melted, and a week of unusually mild weather has brought their flowering stalks to attention, while catching ours. If snow were to fall on them, it’s no matter, as they will patiently wait for it to melt and reveal their long-lasting blooms. Placing Hellebores under a deciduous tree or shrub will give them sun early in the season, and shade later. The foliage is leathery yet quite handsome, and effective all season. I like to clip off last year’s foliage in the early spring, to give room for the new shoots.


Helleborus 'Blue Lady'

It’s little wonder why these superb plants are rarely seen in gardens. Often, they have finished blooming before gardeners seeking springtime cheer are visiting nurseries – all the more reason to do some homework before making a plant purchase, rather than buying what’s in flower. To have four-season interest in your garden requires planning, and patience. To quote W. E. Johns, “One of the most delightful things about a garden is the anticipation it provides.”


Helleborus 'White Spotted Lady'

Fall: The World’s a Stage

“Hardy” mums. I just don’t get them.

Rather, I don’t understand why people continue to plant them, when there are better choices for the fall garden (more about those in a moment.) Sure, they’re colorful: bright beacons of hope that perhaps the frost-free days of early autumn will last a bit longer. But these beacons are often as subtle as airport landing lights – unblinking yellow or white gobs that fairly scream, “Look at me!!!” when the brilliant harmonic tones of the maple, the birch and the sumac – the symphony of the season -- is reaching its colorful crescendo before falling to the ground in a whisper.

The calmer pinks, bronzes and oranges of mums are hardly better, as each plant is pinched and squeezed by the grower into a perfect pompom of flowers with no greenery to dilute the effect; an unnatural natural object in the landscape. And the term “hardy mum” is a bit of a misnomer, as these highly bred beauties are no match for a heavy frost which withers their blooms, or for our cold winters, which usually are fatal.

Consider in their place plants which reliably return each year to offer colorful drama without the harsh stage light effects. One that I feature often is an Aster called ‘Raydon’s Favorite’ (Aster oblongifolius ‘Raydon’s Favorite’), with its cheerful bright blue daisies in September and October. Unlike many, perhaps more familiar asters, ‘Raydon’s Favorite’ remains dense and bushy without losing its foliage to disease. It likes full sun, and tolerates drought once established.


Raydon’s Favorite

I particularly like to use it as a companion to ornamental grasses, most of which achieve glory in October. Even after a heavy frost has dealt a crushing blow to many perennials, grasses such as Miscanthus (with its many varieties) are at their peak, carrying silvery plumes above the graceful clumps of foliage. The onset of winter causes the stalks and stems to turn tawny, but they are sturdy enough to shrug off winter snows to provide a quiet presence in the barren landscape. Other ornamental grasses such Switch Grass (Panicum), Bluestem (Andropogon), Fountain Grass (Pennisetum), Indian Grass (Sorghastrum), and many others, continue to please into the fall.


Miscanthus in fall

Threadleaf (or Arkansas) Bluestar (Amsonia hubrichtii) is a simple yet attractive plant with 3 seasons of interest. They bear small blue starry flowers in spring, and by summer have become durable low bushes of long, thin leaves arranged on willowy stems. Perhaps the best is saved for last, as in September the green becomes chartreuse, and eventually golden by October: a perennial with fall foliage. These are best planted en masse, and combine well with bolder- leaved plants to create a contrast of textures, the fundamental way to develop garden interest. Plants for such supporting roles must include Alum Root, or Heuchera, which is not the old-fashioned Coral Bells of your Grandmother’s garden. Today’s Heucheras have been hybridized to offer stunning foliage in a wide variety of colors including lime, chartreuse, peach, burgundy, purple, and near-black. Cold weather often brings out secondary colors and overlays of red or silver.


Amsonia hubrichtii in fall


Heucheras

Black-eyed Susans (Rudbeckia fulgida ‘Goldsturm’) have been out of flower for a few weeks now, but their chocolate cones are a food source to gold and purple finches which will feast on the black seeds until winter. There is a longer blooming variety known as fulgida, still in bloom now with fine bright yellow daisies. Surely these are better than mums! Allow the seedheads to remain on Black-eyed Susans: the birds will benefit, as will anyone who is able to appreciate their blackened skeletons outlined against the snow. For while it is easy to savor the bravura spectacle that surrounds us now, we must find joy in the far subtler qualities of the garden in winter, long after its notes have faded.


Black-eyed Susans

Planning a New Landscape

Home landscapes, whether old or new, are rarely designed or planted with the active lifestyles of today’s homeowners in mind. The same mistakes get repeated, as large-growing plants -- yews, rhododendrons, arborvitae and others -- are installed too closely together, leading to crowding and the need for regular clipping to prevent windows and walkways from being covered in green. It seems that homeowners today have little time to maintain their plantings, and lack the skills to properly prune them, rather than shear and shape into 3-D forms. (The latter can also be said of many landscape contractors.) Such static plantings offer little seasonal change and limited flowering.

In today’s sluggish real estate market, increasing the visual appeal of your home can become a strong selling point now or later. Consider removing overgrown shrubbery and starting afresh with a new palette of plants which will offer reduced maintenance and greater beauty to enhance your home through all four seasons. Include a colorful and diverse blend of small ornamental trees, deciduous shrubs, rhododendrons and mountain laurels hybridized to remain compact, dwarf conifers which rarely require pruning, and season-extending perennials that serve as ground covers to reduce weeding.

These so-called “mixed borders” can be more complex to design, and may require the guidance of professionals. Your local nursery or garden center may be able to provide free or fee-based plans if you bring a scaled drawing of the area to be planted showing the house footprint, walks and other features, entrances and windows (including sill heights.) Be sure to note north, and how much shade the area will receive. Photographs are always helpful.

Better yet, seek experienced garden designers who will visit your home and create a plan for you. The Association of Professional Landscape Designers has an online member list, including those who have become certified by demonstrating professionalism and proficiency. The New Hampshire Landscape Association is another source of landscape contractors and designers.

This article originally appeared in the September 23, 2008 edition of the Amherst Citizen.

Burning Bushes and Fall Garden Color

Ah, September in New England, my favorite month. Cool, dewy nights melt into morning under the warming sun, its rays splashed against an azure sky. Along roadsides and in unmown meadows the brassy yellow of Goldenrod is untarnished, still gaudy yet not out of place among the clumps of restless grasses swaying in the breeze. And in the distance can be seen the early scarlets and oranges of fall, flaming heralds promising the natural, transcendent glory that is October in New England.

And it’s to October we look ahead in our gardens and landscapes, as Burning bushes (Euonymus alatus and varieties) begin to display their sole reason to grow them: brilliant carmine foliage. Two weeks of Technicolor, and fifty weeks of humdrum.

Such ephemeral beauty doesn’t come without a price, however. To produce the color that inspired its common name, Burning bush requires sun, good soil and plenty of water. Lacking one or more of these, the plant will sulk and disappoint you with pale green leaves all summer, which become a lackluster pink before dropping to the ground. A greater cost is to the local environment, as it has been determined that Burning bush is an invasive species (commonly defined as a plant of exotic origin which has aggressively spread beyond cultivation and displaces native vegetation.) In short, Burning bush is a known thug, and has been prohibited from sale in New Hampshire and several other states.

So, what’s a gardener to do?

First, if you have Burning bush in your yard, the choice of whether to keep or remove it is up to you: there is no squad of Plant Police. That said, it certainly is sensible to remove seedlings that may have arisen elsewhere on your property, at the very least.

Second, there are several alternatives to Burning bush, and they are superior, as they offer multiple seasons of interest as well as being native. None will approach the final size of Burning bush (even the “dwarf” variety of which will become a 10 or 12 foot globe,) and the fruiting forms will attract birds.

Here are a few:

Red Chokeberry (Aronia arbutifolia ‘Brilliantissima’) A native shrub, growing 6 to 8 feet tall, with clusters of pure white flowers in spring followed by glossy red berries later in the summer. The berries are edible but astringent, an aspect which yields its common name. Fall foliage is spectacular – a fiery scarlet. Preserves can be made from the fruit which is loaded with Vitamin C and antioxidants.



Black Chokeberry (Aronia melanocarpa ‘Hugin’) Also native, and similar to Red Chokeberry, but bearing inky berries on shrubs that rarely grow above 6 feet tall. Excellent fall foliage.

Diablo Ninebark (Physocarpus opulifolius ‘Diablo’) A superb purple-leaved selection of the native ninebark shrub, becoming reddish-orange in autumn. Handsome burgundy-tinted white button flowers in late spring. To 8 feet tall.

Blueberry (Vaccinium corymbosum and hybrids) Spring flowers, tasty summer fruit, and incredible vivid scarlet leaves in the fall – what more can you ask for? Blueberries are deserving of space in the home landscape for their gustatory as well as ornamental attributes. The Lowbush blueberry (Vaccinium angustifolium) offers itself as a good ground cover, with the same features. Both are native.

Witherod (Viburnum cassinoides) Another splendid, if underused, native shrub, with fantastic fall foliage that leans toward brilliant red adorning hardy bushes rarely growing over 6 feet tall. Add that to the creamy white flowers in spring which become multicolored berries by summer, and you’ll forget about Burning bush. And the same qualities can be given to the closely related Possomhaw, Viburnum nudum ‘Winterthur’.

A few exotic (but decidedly non-invasive) options:

Paperbark maple (Acer griseum) Growing to twenty-five feet tall, more or less, with excellent red to orange fall foliage. Named for its exfoliating, cinnamon-colored bark which provides year-round interest, but particularly in the winter.

Japanese maple (Acer palmatum and varieties) Most commonly found in its burgundy-leaved forms which offer stunning fall tones of red and orange, but even the green-leaved types can transmute into exquisite cerise hues that rival rubies. Growth heights from six to twenty feet.

Red-veined Enkianthus (Enkianthus campanulatus and varieties) Fall foliage is variably red and orange, but can include purple tones. Lovely dangling bell-shaped flowers in spring. Although capable of growing large, it rarely seems to exceed 10 feet tall in New Hampshire, slowly developing a picturesque branching habit. Of Asian origin.

Any of these shrubs can be safely planted until about the middle of October. They, and many others not mentioned, will do more than simply light up your fall garden. They will delight you throughout the year.

Zoned Out

I have lived in southern New Hampshire all of my life (well, so far at least), and recall cold winters, mild winters, and those that fall somewhere in between. Although a rare occurrence, I do remember low temperatures on bitterly cold January nights dropping in the mid-teens below zero (that's about -26 degrees C, for you of the Metric persuasion.) More typical is the winter when the lowest it's apt to get is around -10 degrees F, but, again, it can get colder. (And let's not even talk about wind chill.)

I bring this up because I recently read that the Arbor Day Foundation has re-scaled the USDA Hardiness Zone Maps, and that southern New Hampshire, like most of the US, has gone up a zone of hardiness, in our case from USDA Zone 5 (minimum -20 degrees F.) to USDA Zone 6 (minimum -10 degrees F.) These maps are generated by the USDA, and are supposed to be updated every 15 years. The last one was done in 1990, so we should be due for another one in 2005. (Wait a minute, isn't this 2007? Well, I'm sure those folks at the USDA have better things to do, such as helping "dole" out advice for the banana orchards and pineapple plantations that are sure to be springing up across the country.) The Arbor Day Foundation took the same data that the USDA uses, and produced this new map:



Is the climate truly changing? Who knows. Evidence seems to be leaning that way, especially given the recent U.N. report on the subject. It's true that this has been an unusually mild winter in New England, as have most of the recent ones been. It was warmer on Christmas (45 degrees F) than it was on Easter (40 degrees F), and on January 6th we hit 69 degrees!

It's interesting, though, to listen to shoppers who come into The Mixed Border and ask for plants that are hardy to at least USDA Zone 4 (minimum -30 degrees F), and who live mere miles away. They cite previous problems with plants not surviving our winters, and suggest they live in a particularly cold spot. In truth, the reason their plants may not survive the winter may have less to do with how cold it gets, but how warm it was before it turned cold. In other words, having a prolonged warm fall, with nighttime temperatures that remain above freezing through November and into December, can be injurious, and sometimes fatal, to plants that are otherwise hardy. Dormancy is delayed as these plants are often the victims of a cruel deception, carried out by a capricious climate that pays the calendar no heed. For no matter how mild the fall and early winter, the icy hammer will surely be swept down from the north, carried in a frozen, unforgiving grip. Just a bit later than normal, and a hardiness zone milder.

And here we are, in early April, less than a week after the most recent storm that laid down a half a foot of slushy crisco snow over the unsuspecting snowdrops and crocuses, not to mention the pots of plants that we just uncovered from their protective winter blankets. We have had more snow in March and April than we had from November through February, and more is forecast for Thursday. With Opening Day at the nursery just 2 weeks away and counting, we are behind in our preparations, but are as eager as every other gardener to see something green.