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.

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