Lee Valley & Veritas

Gardening Newsletter
  Volume 8, Issue 9 - September 2013  
 
Fall Gardens to Rival Any Season
  Colorful fall bloomers
  Japanese forest grass with pink dahlias, great blue lobelia and rudbeckia
Many gardeners don't realize the full potential of the autumn garden. This is a shame, as the fall season seems to be getting longer and longer, especially where I live in southern Ontario (Canadian hardiness zone 6). The lower temperatures and welcome rains offer ideal growing conditions, and for those starting a garden or contemplating a major renovation, garden centers often greatly discount their plants at this time of the year, a real bonus.

Designed to Please
From a design standpoint, autumn is a season of change, as plants dress and undress their foliage wardrobes. These changes, sometimes rapid, sometimes slow, create a dynamic garden with ever-changing plant focal points.

The fickleness and timing of these changes, induced by temperature, moisture, daylight and plant stress, create challenges for both new and experienced gardeners. This is likely the reason we see so many planters filled with ornamental cabbage, kale, pumpkins and chrysanthemums. These same plants, however, can do double duty by filling holes in borders left by disappearing summer perennials. To make the best of the season, visit nurseries, garden centers and botanical gardens to get to know fall plants.

The way we view our gardens also changes in the fall. During spring and summer, our eyes are glued to the ground looking for emerging plants. In fall, the ground plane loses much of its flower power and our eyes shift upwards to the shrub and tree level. Finally, as shrubs and trees drop their leaves, the garden opens up. This can be good or bad depending on what comes into view. Unpleasant sights may warrant screening with conifers and the relocation of movable focal points.

Autumn-season plants can be confined to certain areas of the garden, but I prefer to spread them out to create repetition and the opportunity to view them from multiple locations. Anchor plants such as the spectacular fall-blooming witch hazels (Hamamelis virginiana), fothergillas (Fothergilla gardenii and F. major) and Japanese forest grasses (Hakonechloa spp.) go a long way to tie fall plant compositions together.

 
Arkansas blue star and blue-flowered aster
Arkansas blue star (foreground) and blue-flowered aster (background)
 
Plant form, texture and seed heads take on added significance in autumn, as the palette provided by flowering plants diminishes. This is particularly the case if your goal is to create extra depth by using finer textures in the background and bolder textures closer to decks and patios.

One of the most dramatic plants in terms of texture is the Arkansas blue star (Amsonia hubrichtii), which has striking orange-yellow, thread-like foliage. It combines beautifully with the blue flowers of the fall-blooming New England aster (Aster novae-angliae) and the remarkable red-twig dogwood (Cornus alba 'Sibirica'). The seed heads of many perennials such as the coneflower (Echinacea spp.), black-eyed Susan (Rudbeckia hirta spp.), blackberry lily (Belamcanda chinensis) and ligularia add further color and interest.

A summer palette of warm reds and yellows can be extended into the autumn. Try the purplish-red foliage of 'Little Henry' sweetspire shrub (Itea virginica 'Little Henry'), rodgersia (Rodgersia spp.), tree peonies and various heucheras. These are complemented by the buttery yellow foliage of redbud (Cercis canadensis), Carolina allspice (Calycanthus floridus) and Solomon seal (Polygonatum biflorum).
 
Frost-nipped heuchera
The frost-nipped edges of heuchera create a dazzling effect in the autumn garden.
 
Fall light is less direct and at a lower angle, which produces brighter hues and interesting backlighting effects. Examples of vivid backlighting can be seen on Japanese blood grass (Imperata cylindrica 'Red Baron'), various Japanese maples (Acer palmatum), Flame Amur maple (Acer ginnala 'Flame') and New Zealand flax lily (Phormium spp.). Though early frosts are often a concern to gardeners, they can also produce some interesting effects. Consider frost-nipped heucheras. The crispy-white edges make them look much like salt-rimmed margarita glasses.

Fall Foliage Specifics
Fall color change is not limited to just deciduous plants. Conifers such as the Juniperus horizontalis cultivars 'Plumosa Compacta', 'Bar Harbor' and 'Prince of Wales' take on a rich plum-purple coloration, while others, including larches (Larix spp.), have needles that turn a brilliant gold before dropping. Black mondo grass never changes color, while sweetgum (Liquidambar styraciflua) and various serviceberries (Amelanchier spp.) may be red one year and yellow the next.

A plant group that stands out for its striking amber color and variety of spectacular forms is ornamental grasses. These plants combine beautifully with late-season border perennials and meadow species such as black-eyed Susan (Rudbeckia hirta), ironweed (Vernonia spp.), goldenrod (Solidago spp.), aster and Joe Pye weed (Eupatorium spp.). See the article Ornamental Grasses (Vol.7 Issue 7) for additional information.
 
Black-eyed Susan with geranium   Fall-blooming ironweed
Cheery black-eyed Susan mingling with blue-flowered geranium 'Rozanne'   The gorgeous fall-blooming ironweed adds vibrant color to the fall garden.
 
Fall Flower Power
It may surprise some gardeners to learn that there is a wide variety of annuals, perennials and woody plants that bloom reliably each fall. In some cases, the name of the plant suggests its fall worthiness, such as sweet autumn clematis (Clematis terniflora) and autumn monkshood (Aconitum carmichaelii). One of my favorites is the shade-tolerant toad lily (Tricyrtis spp.), with its small orchid-like flowers in white, pink and lavender.

The bugbanes or actea species, particularly the dark-foliage ones ('Brunette', 'Hillside Black Beauty' and 'Pink Spike') with their spectacular wand-like white or pink flowers, are popular fall subjects. To contrast with gold foliage, consider deep-blue bottle gentian (Gentiana andrewsii) and autumn monkshood. For pink flowers, add 'Luna Pink Swirl' hibiscus (Hibiscus moscheutos 'Luna Pink Swirl'), 'Autumn Joy' sedum and Japanese anemones (Anemone hupehensis cultivars), which make wonderful companions to the amber glow of fountain grass (Pennisetum spp.).
 
Toad lily
The truly distinctive toad lily is an eye catcher in any autumn garden.
 
One of my favorite tall shrubs for autumn is the Seven Sons flower (Heptacodium miconioides), with its fragrant white flowers that bloom during September and October, followed by what appears to be a second flush of pink flowers in late October. (These are actually calyces or small petals that protect the real flowers). Other desirable fall shrubs include native witch hazel, with its fall clusters of yellow ribbon-like flowers, and for butterfly lovers, the bluebeard shrub (Caryopteris spp.) and butterfly bush (Buddleia davidii). For grapefruit-sized blooms, try Annabelle hydrangea (Hydrangea arborescens 'Annabelle').

To extend the flower period, deadhead the spent blooms on marigolds, zinnias, snapdragons, salvia, coneflowers, balloon flower, turtlehead and blanket flower (to name a few). This practice puts the plant's energy into producing more blooms and reduces freely seeding plants. Colorful fall berries often follow the flowers, and there are lots of great choices such as 'Profusion' beautyberry (Callicarpa bodinieri 'Profusion'), the white fruits of snowberry (Symphoricarpos albus) and the colorful berries of cotoneasters, barberries and viburnums.
 
Seven Sons Flower
The lovely and delicate white blooms of the Seven Sons flower
 
Fall Maintenance
Autumn is a good time to divide older plants and plant new ones, as long as they have ample time to establish their roots before winter. Since the garden is more open, meaning you'll likely do less damage, it's also a good time to apply compost, manure and mulches to beds and borders. Use a lawnmower to shred leaves, especially thicker oak and beech leaves, and apply them to beds and borders to help insulate the soil and minimize winter-root dislodgement.

Dispose of fleshy foliage such as that of hostas, as it tends to turn slimy and harbor overwintering slugs and snails. Be careful when applying fertilizer in fall, as it can stimulate new growth. To prevent this, I let plants harden off naturally. My woody plants that are exposed to salt spray from roadways are wrapped in burlap, and I place cardboard tubes filled with leaves around young seedling trees to protect them.

During a dry autumn, it's a good idea to ensure that evergreens, including broadleaf evergreens such as Oregon grape (Mahonia aquifolium), rhododendrons, pieris (Pieris japonica), laurels (Kalmia spp.), hollies and ivies go into winter with roots that have a good moisture reserve. This will help prevent winter desiccation.

Autumn is much more than an encore or shoulder season to the summer. It should be embraced as an exciting time to plan, plant and enjoy the garden as nature intended.
 
Text by Frank Kershaw

Photos by Marnie Wright

Frank Kershaw is an award-winning horticulturist with more than 35 years of experience. He teaches garden design and horticultural courses at George Brown College in Toronto, Ontario, and at the Toronto Botanical Garden. Frank is also a presenter at the Lee Valley seminars at the Toronto stores.

Marnie Wright (gardenwright@muskoka.com) is a lifelong gardener, writer and passionate garden photographer. Her Rocksborough Garden, developed over 30 years, is located in Bracebridge, Ontario.
 
 
 
 
     
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