Zone 6  has a medium-length growing season, with a frost-free period that lasts from mid May til late September.
U.S. cities within this zone include Boston, Buffalo, New York; Chicago; Columbus, Ohio; Kansas City, Missouri; and Pittsburgh, Pennsylvania. The average lowest winter temperature is between -10 and 0 degrees Fahrenheit. You can grow a wide variety of plants in this hardiness zone, and I do.

There are thousands of plants that you can grow in your garden, but if you want to grow varieties that are proven winter hardy, or those that can take high temperatures and other extremes, choose perennials appropriate for your state and region. You can have your cake and eat it, too, if you treat non-hardy plants as annuals, and either re-plant in the spring, or try to winter them over as houseplants or dormant stock indoors. I've had great success with hanging succulents, herbs, bamboos and dwarf fruit trees by wintering non-hardy varieties indoors.

Remember that lots of plant families contain plants for cooler or hotter regions. For instance, I grow Giant Hibiscus in Zone 6. There are many hardy varieties for my region. There are also "tropical" Hibiscus, which will die at the first frost in the northern states. I made that expensive mistake only once, and I pay more attention when buying from online nurseries and plant sellers. Not all are labeled or specified as hardy, and not all listings give you the hardiness zone information. Most garden centers in big home centers sell plants that are labeled by the growers, and for the most part, the employees are not horticulturally savvy.  Mislabeling, missing labels, and bad information is commonplace. 

If unsure, check the extension services in your area for the plants that do best in your climate, then check the USDA plant hardiness zone map.

It's always best to get your special and valuable landscape plants from a grower or reputable plant nursery. Do not make the assumption that if a plant is being sold in your area, it will thrive and survive. You will also want to check for potential invasiveness. I've seen plenty of invasive plants being sold without that important information. I do not want invasive plants to become a nuisance or plant killers in my gardens. I once lost a battle, and many perennials, with invasive Lantana. Very pretty, but impossible for me to get rid of. Mints are also notorious invaders in that category. Wisteria is another cloaked in accolades and secrecy - I grow 2 tree wisterias that are non-invasive, and I trellis them, prune them into shapes I want, and grow them in big pots. I've seen the structural and tree damage Wisteria vines do in the south, and many places now have it on their lists of invasive species. There are non-invasive species of just about any invasive plant, so don't give up on a plant, just look into it.

Here is an official list of Pennsylvania's invasive plants. It's a comprehensive list of damaging and invasive plants in the state, complete with fact sheets you can read and download.

I treat invasive plants with a little grain of salt, as I control the growth of all of my plants. Either with severe pruning and thinning, or by growing them in controlled environments, and in pots or on trellises. Some of my plants are considered invasive in regions, but I have not found them to be. I deadhead as much as I can so that a plant doesn't go to seed, but will probably re-bloom for me. There are a lot of destructive plants growing wild and crowding out roadways, damaging pipes and structures, and strangling native growth, so it's wise to just not grow those or at least, don't grow those in an open area on large properties or in wildflower or prairie gardens.

Native plants for each state are the best choice. You know they thrive in your region. For Native Plants and Wildflowers that flourish in Zone 6 in Pennsylvania, visit the Pennsylvania USDA Native Perennial Plants Database. You can search for native plants for any state and region.

Check out this page for more growing information - Pennsylvania USDA Hardiness Zones 5/6 - Native Plants and Their Attributes

 

Below is my list of perennial plants and trees appropriate for growing in Pittsburgh and other Zone 6 areas. Check for the proper variety of these plants. Some varieties won't make it through your winter, no matter what the Zone hardiness is for that species. Some types are hardy, some types are primadonnas. This is not an exhaustive list. It's mostly what I have successfully grown in both of my own Zones 5 and 6b gardens.

The * next to the plant designates that the species has proven hardy in my gardens in Pittsburgh. In-ground and in pots.
Remember that gardens have "microclimates". So not all plants designated as "tender perennial" will be hardy (or not) in every garden, or they may be perfectly hardy. My gardens have sheltered areas, or "rooms". I can grow a lot of things in my microclimate in those sheltered spaces that normally do not survive winter. Using this logic, there can also be microclimates in your gardens that can reduce the cold hardiness - windy, wet, damp, chilly, exposed, sloping high or low, growing in containers, etc. I also grow plants designated for shady areas in the sun, and vice versa. Researching your plants and knowing your garden spaces is essential. I can grow some borderline trees
that are winter hardy by clustering potted trees in a sheltered area behind a fence, and against a warm exterior wall.

Check your plant names and hardiness zone listed for them on the USDA cold hardiness zone map, to be sure the variety you pick is perennial in your zone.

Popular Zone 6 Flowering Plants and Shrubs

Forget-Me-Not
Evening Primrose
*Buttercups
Catmint
Poppies
*Penstemon
*Rose of Sharon
* Giant Hibiscus
*foxglove
*larkspur
*hollyhocks
*delphinium
*chrysanthemum
*Mugwort
forsythia
*Milkweed and butterfly weed
*Butterfly Bush
*Coneflowers
*Agastache
*Snapdragon
*Aquilegia
*Lupines
*Cardinal Flower
Crocosmia
Delosperma
Heuchera
Tansy
Feverfew
Culver's Root
Dutchman's Breeches
Trillium
Shooting Star
Virginia Bluebells
Helenium
Helleborus
Ninebark
*Chokeberry
Chokecherry
Beautyberry
*Elderberry
*Daisy
*Black/Brown-eyed Susan
*Sea Holly
*Astilbe
*Sweetspire
*Summersweet
*Weigela
*Mock Orange
*Hydrangea
*Aster
*Bee Balm (Monarda)
*Violet/Viola/Pansy
Lady's Mantle
St. John's Wort
Chamomile
Baby's Breath
*Veronica
*spirea
*Bleeding Heart
Liatris "Blazing Star"
American Wintergreen
Gentian
Goat's Beard
*Bishop's Weed
Wild Ginger
*Lavender
*Salvia
*Viburnum
*Achillea (yarrow)
Red Hot Poker
*Lilac
*Rhododendron
*Nandina "Firepower"
* Shrub, tree, and climbing Roses
*Rugosa Rose
*Scabiosa
Amaranth
Angelica
*Campanula
*Coreopsis
Deutzia
*Dianthus
Gaillardia
Geum
*Hardy Geranium
*Knautia
Lewisia
Linaria
Monkey Flower

Liriope
*Russian Sage

Baptisia
Japanese Anemone
Baneberry
Lobelia
Hepatica
Jack in the Pulpit

Perennial Culinary and Medicinal Herbs and Veggies

*Oregano
*Echinacea (coneflowers)
*Sage
*Thyme
Wormwood
Betony
Rue
Comfrey
Chervil
Dill
Shallot
*Garlic
Sorrel
Savory
*garlic chives
asparagus
*horseradish
*rosemary
Arugula
*Lemon Balm
Lemon Verbena
*All mints
Feverfew
Tarragon
St. John's Wort
Chamomile
Tansy
Goldenseal
*Dandelion - edible and medicinal weed
*Purslane - edible weed
Black Cohosh, Blue Cohosh
Bloodroot
*Roses - Hips are packed with vit. C, petals used in teas
Angelica
Valerian
Fennel
*Yarrow
Lovage
Pennyroyal
*Scallions/ green onions

Ornamental Foliage Plants and Ferns (some of these plants also have flowers)

Heuchera
Brunnera
*Amsonia
Cushion Spurge
Hakone Grass
Pulmonaria
*Maidenhair Fern
*Hosta
*
Mahonia
Holly
*Dwarf hardy Bamboo
*Dwarf Yucca - "Color Guard"
*
New York Fern
*Autumn Fern
*Japanese Painted Fern
Deer Fern
*Wood FernSword Fern
*Artemisia
Lady's Mantle

Popular Flowering Perennial  Bulbs, Rhizomes, Tubers and Roots

Most spring flowering bulbs, except for tropical varieties, are hardy in the colder regions, where chill hours are quite essential to spring flowering. Within all groups are several examples of zone differences between varieties.

*Lilies
Daylilies
*Peonies
*Iris
*Tulip
*hyacinth
*daffodil
*crocus
*perennial gladiola
Allium
*Louisiana Iris
*lily of the valley

Favorite Flowering and Fruiting Vines

*Sweet Pea
Four-O'clock
*Periwinkle
*Morning Glory
*Virginia Creeper
*non-invasive varieties of Honeysuckle
*Clematis
*non-invasive varieties of Wisteria
*Trumpet Flower
Grapevines

Groundcovers

*creeping phlox
*snow in summer
*sedum
*ivy
*Blue and White Star Creeper (Amsonia)
*Hardy Geranium
*Snow on The Mountain
pachysandra
*Creeping Jenny
*Creeping thyme
*Mountain Laurel
*Hens and Chicks
*Ajuga
*Lamium
*Periwinkle

Barrenwort
White Clover

Hardy Succulent/Cactus

*sedum
*Opuntia (prickly pear cactus)
*Dwarf Yucca - "Color Guard" and a few others
*Hens and Chicks

Conifers and Ornamental Evergreen Plants, Shrubs, Trees

*Juniper
*Cedar
Cypress
Norway Spruce
*Rhododendron
*Dwarf Mahonia
Holly
*Arborvitae
Weeping Atlas Cedar
*pines
*Balsam fir
*Dwarf Bamboo
*Hardy Camellia
*Euonymous
Abelia
Cotoneaster
*Boxwood
Yew
Oregon Grape
*Mountain Laurel
Bearberry
Winter Heath
Ornamental Trees - Dwarf varieties grown in pots included on the list.

Many standard ornamental and fruit trees can be dwarfed for small spaces, and many can be trellised and espaliered to conserve space , and used to decorate walls, structures, and fences.

*Wisteria Tree
*Purple Leaf Plum ("Thundercloud")

Amur Maple
*Chinese Fringe Tree
*Japanese Maple
Pussy Willow
Magnolia
*Ornamental Plum trees
*Redbud/Weeping Redbud
*Dogwood
Flowering Pear
Flowering Almond
Sugar Maple
*Japanese Weeping cherry
*Snow Fountains Cherry
*Snowflurry Cherry
*Japanese Snowcherry
*Ornamental Cherries
Catalpa
Golden Rain Tree
Mimosa
Tulip Tree
*Weeping Willow
Ninebark
Hardy crape myrtle

Lots of Perennial Fruit Trees, plants and shrubs. Edible and ornamentals

*Strawberries -  several types of June- and everbering
blueberries
*blackberries
*raspberries
*elderberries
*honeyberry
*mulberry
Goji Berry
boysenberry
Logan Berry
*cherries - many types
 Salmonberry
Lignonberry
huckleberry
cranberry
boysenberry
kiwiberry
seaberry
*chokeberry
*chokecherry
currants
gooseberries
jostaberry
*Apples
pears
asian pears
*apricots
*nectarines
*peaches
*plums
grapes
pomegranate
olive
Figs: I haven't tested cold hardiness of the hardiest yet.... my trees are going into their first winter. All are growing in moveable pots.

The following fig varieties are said to make it through Pittsburgh's Zone 6 winters, with shelter and protection:
Brown Turkey Fig, Chicago Hardy Fig, Celeste Fig, Kadota

- A borderline zone variety's hardiness depends upon the actual severity of winter weather in the northeast. And yes, where it's at in your own backyard. Some zone 7 figs, like Kadota and Celeste, can survive Zone 6 winters with protection.

Fig trees in the northern states should be wrapped, covered, or trenched in fall. When all the leaves drop, the trees can be brought indoors, or stored in a cold garage, basement or shed during the entire winter dormancy.

Dormant plants do not need sunlight, and very little water until they break dormancy in early Spring. Pruning can be done during dormancy. Fig trees can be planted outdoors early... as soon as they break dormancy and the ground can be worked. They need a long growing season to produce the main fall crop.

Ornamental Grasses - planted in soil, bogs, in marginal bog areas and in or around ponds

*Arrow Grass
*Fescue - "Elijah Blue" , all festuccas/fescue
*Japanese Blood Grass
*Sweet Flag
*Sedges
*Rush
Hakone Grass
*Corkscrew Rush
*Muhli Grass
*Dwarf Cattails
*Bluestem Grass
*Blue Oatgrass
Pampas Grass
Liriope
*Black Mondo Grass

Horsetail Reed
Sea Oats
*Miscanthus
*Fountain Grass
Switch grass
June Grass
*Maiden grass
*Carex

Hummingbird and Butterfly Plants

Food For The Bees

Habitats For Birds

 

Sources, other than my own gardens:
Breck's
Stark's
USDA
Pa. Dept. of Natural Resources
Penn State Cooperative Extension
Proven Winners
Better Homes and Gardens

 

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