FERNS
Hostas
Astilbes
Chelone
Peonies
Polygonatum
Echinacea
Ornamental grasses
Baptisia australis

I agree with chelone on Baptisia & many others-garden would not be as beautiful without this plant. But give it lots of room to spread! Grasses, Hosta, Astilbe, I'm also a big fan of roses-I have 7 bushes that I love. Vines-honeysuckle and grape vine over an arbor. I have a large Yucca up front and 3 Arborvitae at the corner of the house. The back is really tough to garden in because its so moist. I need to build up areas there. Daylilies are a real focal point when they're blooming.

Jen

Gimme some more time. After 50 years, the only must have is grasses.

Donn, how much more time do you want?

My must haves are salvias, dahlias, lilies. All are big splashes of color that stand out and anchor a planting.

Roses. In my full sun gardens, everything is planted around my roses. They are one of the few flowers you can count on for constant color from spring to hard freeze. They also give me an endless supply of blooms to bring to work.
Iris,peonies, daylilies, rudbeckia, salvia are also workhorses that I use a lot of. I don't care for the 'big drifts' design so I mix things up with smaller patches of yellow, orange and purple. Pinks accented with silver and blues.

In the shade, ferns and hostas.

For me, it's geraniums (I find a new variety, it comes home with me), asiatic and oriental lilies, peonies, and salvia.

I also have a soft spot in my heart for "fluffy" daisies (crazy daisy and the like). And you can't have a perennial garden without echinacea.

(assuming we are talking sun here, since the list would be very different for shade...)

Clematis
roses
geraniums
catmints (Nepeta sp.)
Salvias
Asters (and relatives)
Grasses
Veronicas(trums)
Monardas
Daylilies
Phlox
Siberian iris
persicarias
digitalis

etc, etc, etc

For me, the perennials that I have repeated in every garden are:

geraniums, various
echinacea, purple
daisies
nepeta
daylillies, various
rudbeckia

I find I'm pretty much guaranteed a good show of colour with these ones.

tess

I'm not sure I'd consider any perennials as "backbone" plants specifically, but I lean towards those that have a year round presence, i.e. more or less evergreen. Euphorbias, heucheras, evergreen grasses or grass-like plants, hellebores, bergenia, and heaths and heathers and other evergreen goundcovers are planted throughout my gardens and I'd not like to do without them. I have much less of an interest in the more standard herbaceous perennials and those that I do include generally need more than just flower power to fill the bill. There are a few exceptions, however :-)

I agree with gardengal48. My backbone plants are the ones I can count on for some green all year. I love my yarrows, verronic, and verbenas. Now, my can't live without plants for my tropical garden are my cannas, elephant ears, and banana trees.

daffodils - many different old fashioned fragrant varieties
daylilies - the old fashioned double and single orange
iris - yellow flag and a number of passalong Germans that I have no idea of the name
garden phlox
echinacea
callas
buddlia
vitex
roses
French mulberry
kerria
broom
yarrow

Becky

I am not sure how to answer- backbone to me is something that keeps structural interest year around and in my zone very few perennials evergreen. So backbone are shrubs and conifers which save my garden during those months when nothing much out there. If we are talking about architectural plants that have imposing presence in my shady garden will be rheum palmatum, rodgersia, crambe cordifolia, cimicfugas, aconitums, various clematises, macleya cordata, ornamental grasses, various ferns, hostas.

I guess I should clarify- the term 'backbone' was probably not the best one. I agree that shrubs, trees and garden structures/ornaments form the skeleton for the mixed border.

However, in order to maintain some sort of umph and order, I typically repeat several perennials in the landscape. It serves as a unifying feature and creates rhythm in the border. Obviously, the best plants for the task are long bloomers or stunning foliage. There are a lot of perennials that can fit that bill and wondered what others use.

My short list of "backbone" perennials:

salvia nemerosa 'East Friesland'
intermediate bearded iris 'Bluebird in Flight'
daylily 'Happy Returns' & 'Mini Pearl'
garden phlox 'John Fannick'
Japanese holly fern for shade (for those in zone 7b & warmer)

Randy

This is a weird one, I'm sure... but I really like to repeat bronze fennel in the garden. I like the dead skeleton of the plant in the winter, I like the soft purple foliage, it looks good with both hot and cool colors, and it takes a decent bit of shade, too. If the yellow flowers don't combine well with what it's around, I clip them off.

Other than that, I like grasses and grass-y foliage (Siberian iris, crocosmia), and repeating rounded foliage like alchemilla mollis in shady areas, hollyhocks in sunny ones, and squash vines in a third.

I have just been looking at the lists that I made last year for my planting of my new yard this year. To me in New England backbone plants in a perennial garden are ones that have attractive substantial foliage spring through fall and blooms that I like. I have listed peonies, Baptisia, Siberian Iris and Playcodon. In recent years I have also added Amsonia Hubrechti and chocolate Eupatorium. There are other plants I would not want to be without, but these ones all have wonderful foliage in different shapes and colors to balance each other and I want a scattering of them across the mid to back or the gardens.

Some of my best performing perennials for sun are:

Ornamental grasses -
Panicum 'Heavy Metal' - upright, good fall color
Calamagrostis 'Karl Foerster' and 'Overdam'(variegated) - bloom early for ornamental grasses, easy to divide
Pennisetum orientale - blooms early and heavily
Miscanthus 'Purpurascens' - more upright than most miscanthus, great fall color

These are some of my longest blooming perennials:
Geranium 'Rozanne' - blooms spring to frost
Veronica 'Goodness Grows' and alpina alba - bloom spring to fall, good edging plants, no mildew
Nepeta 'Blue Wonder'
Salvia 'May Night', 'East Friesland', 'Blue Hill'
Calamintha neptoides (may seed a bit)
Ceratostigma plumbaginoides - good groundcover (creeping roots) to use with spring bulbs since it wakes up late, true blue flowers summer to fall, red leaves in fall
Echinacea 'Magnus', 'Kim's Knee High' (I bought some of the newer kinds this spring but haven't had them long enough to judge yet)
Achillea 'Appleblossom' - spreads from roots but not nearly as bad as some other achilleas
Perovskia - a good background plant

Salvias, echinaceas, veronicas, calamints and nepetas also attract lots of butterflies and bees.

Although they don't bloom quite as long, daylilies are my favorite flowers, for their beauty and amazing variety.

If you have a large trellis, clematis viticella 'Betty Corning' is a vigorous vine (no wilt) with many lavender bells over a long time.

Juliet

This is my 3rd move within 6 yrs and I always start off by planting these: dark colored Phoriums, phlox paniculatas, salvia guarnitica, variegated cannas, russian sage, ornamental grasses, sum and substance hosta, lilies.

I repeat salvia -Blue Hill, May Night, Caradonna - purple does with everything! I have an enormous persicaria polymorpha that I would definately describe as "backbone".
I also like to use hostas, pulmonarias, heucheras (Peach Flambe is amazing), dwarf iris and daylilies, tradescantia and geraniums. They can tuck in just about anywhere.

Plants that make the big show and I would not want to be without:

Daffodils
Lupins
Daylilies
Delphinium
Plox
Geraniums

My backbone palnts for me are those that provide intrest throughout the growing season. My favorite tree would be my curly willow. I call it a screwy willow. lol. For year round I have to agree with the bronze fennel.

Blackswampgirl- how do you divide your? oh and you have excellent taste. mine is planted with Russian sage and I love the contrast.

Also of course hostas, varigated iris. i am currently working on adding in more interesting foliage plants. it's to easy for me to buy the pretty flowers not thinking about when they are done blooming they arn't as pretty.

My favorite backbone plants are:

Baptisia
Peony
Siberian Iris
Roses
Clematis
Amsonia
Echinacea
Aster
Ornamental grasses
Sedum
Hibiscus

Mainly I like perennials that, even when not it bloom, have nice foliage for most of the growing season. I am trying to get away from plants that die back after blooming. I don't like the big holes they leave when they go dormant.

Lori

For my garden it would be:

Roses
Peonies
Catmint
Perennial geraniums
Salvia
Asters
Purple coneflowers
Daylilies
Phlox
Helianthus
Sedum
Grasses
Lambs ear
Clematis
Shasta daisies
Monarda
Rudbeckia

These are plants that I use over and over in the garden. I also search for different varieties of a given plant family, so for Peonies I have over 50 varieties.

In Utah, you should take most of those lists with a grain of salt. Utah's climate is very different from the central and eastern part of North America. I live in eastern Washington, which is much colder than Utah but has some similarities in climate patterns (semi-montane). The perennials that do well where I live often do poorly east of the Rockies and vice-versa.

I'd plant a wide variety of things to start and see which thrive and which struggle.

For me, small tufted ornamental grasses, mostly fescue, are probably the most constant perennial, but you should avoid planting grasses next to the house as they provide year-round foliage that shelters rodents and bunnies.

Kelly

Roses, Encore Azaleas and Salvia. I'm trying Baptisia this year for the first time and suspect it will get added to the list.