Go with what works, like lupines along the craggy North Shore. Soil conditions some plants might find taxing are perfect for others. Keep experimenting until you find what thrives in your garden.
You don't need lots of variety to have a great garden. Zone 3 gardeners have fewer options in their gardening design arsenal, but still can manage some lovely displays. Concentrating on proper spacing, relative heights and careful use of repetition win the day.
Embrace annuals. I've been exposed to a form of snobbery that makes me feel like it's cheating if I resort to annuals in my garden. All those cheerful window boxes in resort cabins remind me that annuals provide a great color day brightener. Life, and summer, are too short not to enjoy them.
Reducing stress on the garden reduces stress on the gardener. I saw lots of thriving plants, partly because they weren't heat stressed, so peony season lasts longer. Shade-appropriate plants enjoyed their tree-topped yards, and sun-lovers enjoyed the strong rays. I'm guilty of pushing the issue in one border in my yard where all but 10 feet are in shade. I spend more time watering and coaxing along the plants in that short stretch than the rest of the border put together. Time to give those coral bells, and me, a break by subbing in some true sun lovers.
Protect what you've got. In some cases, that meant high fencing around the pristine yards to keep deer from venturing in from the nearby woods. In other cases, I'm guessing it means slug-repelling measures, as I saw signs of their trails each morning.
There's a discipline and challenge that zone hardiness brings to any garden. While those of us in Zone 4 might not have quite the same badge of honor that those farther north do, we've at least got a few merit badges. That doesn't mean I won't still have a touch of Zone 6 envy when January brings us cold snowy weather and garden catalogs filled with lots of pretties we can't grow as perennials.But if you really, really want to grow that gorgeous Zone 9 plant, cheat and treat it as an annual, or try growing it in a pot you bring indoors in winter.