Perennials for Difficult Sites
If you have good drainage, reasonable moisture and sun to partial shade you can easily grow thousands of different perennials.  However if you are gardening in less than ideal conditions your choices can become more limited. Frequently I am asked for plant suggestions for four difficult areas:  Dry Shade;  Hot, Dry, Sandy Soil;  Slopes and Wet Areas.

DRY SHADE
Typically this is an area under trees or against the house under an overhang.  These are areas that don’t naturally receive a lot of rain and the gardener, for a variety of reasons, is unable to provide sufficient water.

In a dry area the first course of action is to improve the soil by adding compost, well rotted manure and bonemeal.  (Do not add peat moss as when it dries out it will actually repel water!) After planting it is important to mulch in order to protect the soil from moisture loss and wind erosion.

So what grows reasonably well in dry shade?  Hosta are a mainstay of the dry, shady garden.  However they are not the only plant that will do reasonably well in such conditions.  Following are a number of perennials to try:
Aruncus aethusifolius – Dwarf Goatsbeard
Alchemilla – Lady’s Mantle – large and small varieties
Anemone – Japanese Anemone – very tough
Anthemis – blooms all summer, for sun or shade
Campanula persicifolia – Peach-leaved Bellflower
Corydalis lutea – surprisingly adaptable to many conditions
Chasmanthium – the best grass for dry shade
Galium odoratum – Sweet Woodruff – wonderful groundcover
Persicaria – several forms, all do well in dry shade
Platycodon – Balloon Flower, sun or shade
Epimedium – beautiful foliage plant
Tradescantia – Spiderwort – blooms all summer

HOT, DRY, SANDY SOIL
There are actually many drought tolerant plants that do well in a hot, dry sunny situation.  As with any difficult garden site it pays to improve the soil and then protect it with a mulch.  Following is an abbreviated list of my favourites:
Achillea – Yarrow – carefree easy perennials
Armeria -  Thrift – wonderful dwarfs ideal for the rock garden
Artemisia  - large variety, great silver foliage, aromatic
Calamagrostis – Feather Reed Grass  -- invaluable!
Cerastium – Snow in Summer – silver leaved creeper
Echinacea  - Purple Coneflower – great ornamental
Echinops – Globe Thistle – wonderful round flowers
Eryngium – Sea Holly – fantastically exotic
Festuca – class ornamental grass – great blue colour
Gaillardia – Blanket Flower – many varieties, blooms all summer
Gaura – Butterfly Flower – great for late summer and fall
Helianthus & Heliopsis – long flowering yellow daisies
Lavander – best blooms and form in dry conditions
Leucanthemum – Shasta Daisies – short & tall varieties
Miscanthus – Japanese Silver Grass – fantastic – love’em
Nepeta – Catmint – many bloom all summer, aromatic
Oenothera – Evening Primrose – many varieties, long flowering
Penstemon – Beardtongue – long flowering , many varieties
Perovskia – Russian Sage – lovely foliage, aromatic
Salvia – outstanding ornamental, many varieties
Sedum – indispensable group, ground-hugging to 3’ tall
Solidago – Goldenrod, new varieties are terrific
Stachys – Lamb’s Ear and other, tough plants
Verbascum – lots of new varieties, reblooming
Veronica – new improved varieties bloom all summer

SLOPES
This is usually a ‘difficult’ area because it can not be easily mowed or is impossible to mow and needs a tough, low-maintenance lawn substitute.  There are several for such a site but I’ll just focus on my two favourites.

For the shade my number one choice would be Lamiastrum galeobdolon.  This is an exceptionally tough, aggressive, spreading plant that does very well in dry shade (like under maples) and other difficult sites.  It has lovely green and silver foliage and produces yellow blooms in the spring.  I planted it in very lean soil under my spruce trees and it is filling-in very quickly.  DO NOT plant this in your border!  Yellow Archangel, as it is sometimes called is hardy from Zone 2-9.

Thymus serpyllum (Mother of Thyme) is an outstanding lawn substitute for a sunny site.  It is a low growing, mat-forming plant that quickly creeps outward and will also self-seed over time.  Once established it will take considerable foot traffic and can even be mowed.  It is covered with masses of pink to purple blooms in late summer.  Once established this is truly one of the few no maintenance plants.

THE WET SITE
A wet site can be the result of many factors – poor drainage, heavy clay soil, a low spot in the garden or perhaps a natural bog area.  Most plants do not like to have persistently ‘wet feet’.  However there are some plants that just thrive in a constantly moist environment.  Again the following list is not conclusive and just reflects some of the most popular and my favourites.
Acorus –  several outstanding varieties, not just for water gardens
Astible – many gorgeous varieties
Carex – Sedges – great garden colour, lots of varieties
Cimicifuga – Bugbane – regal perennial, fall flowers
Eupatorium – Joe Pye, versatile, loved by butterflies
Ferns – many varieties, indispensable for shade
Filipendula – outstanding ornamentals
Hosta – grow them virtually anywhere
Some varieties of Iris including:  Iris ensata, Iris siberica and Iris versicolour
Persicaria – several varieties, all very adaptable
Rodgersia – fabulous foliage plant
Tradescantia – tough plant for sun or shade

   

   
Gardening Tip
I hate plants that get too tall  and start flopping all over the place as soon as they are in flower.  This feeling goes hand in hand with my hatred of staking.  No matter what device is used or how carefully you tie up the offender, the poor thing loses most of its ornamental value and looks like some kind of prisoner.
I have found the best way to get around this problem is to cut back taller perennials by about one half, early in the season. 
Plants like Summer Phlox, Joe Pye, Asters all benefit from being cut back in early-to-mid June.  This produces a more compact plant, bushier, and with more blooms.  All good things!
This pruning practice can be used with most perennials however it is best done before any buds are set.  Even so it will likely delay blooming by a couple of weeks.
   
Feature Plant - Veronica
This old-fashioned group of plants has in recent years been transformed by numerous really outstanding new hybrids.  These new varieties have exceptional vigor, are longer flowering and much more heat tolerant than the older varieties.  This is a very versatile group, hardy to Zone 3, and easily grown in sun to partial shade, in ordinary garden soil.  All are lightly fragrant and attractive to hummingbirds and butterflies.  They can be used in the border, rock garden and even in containers.
I’ll just mention a few of the outstanding varieties that I grow in my garden.
Veronica ‘Eveline’
This beauty blooms all summer.  It has a tight, compact form and produces masses of true pink flower spikes. (24”)
Veronica ‘Royal Candles’
Produces an all summer display of deep violet-blue flower spikes.  Try this with a golden foliage plant like Tradescantia ‘Sweet Kate’. (15”)
Veronica ‘Goodness Grows’
Profuse bloomer.  Blue spikes all summer.  Excellent compact form.  (12”)
Discover more Veronica in our Catalogue.

   
Great Combinations
Spring is coming and I love that purple-gold combination produced by Aubrieta and Aurinia – Purple Rock Cress and Basket of Gold.  Add a few Primroses and some dark-leafed Labrador Violet (Viola labradorica)  and  PRESTO! you’ll have weeks of colour in your garden.