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Early spring is the perfect time to start planning and prepping our gardens. Will you go edible or prairie? Cottage or contemporary? As we break down the mood boards and designs, it’s worth pausing to think about a few key factors that can make or break your perennial garden.

Even experienced gardeners make these mistakes — but the good news is, they’re all easy to avoid with a little planning and attention. Here are eight common perennial garden pitfalls and how to steer clear of them.

1. Ignoring Your Hardiness Zone

Minnesota spans three USDA hardiness zones: Zone 3 in northern Minnesota (we’re talking to you, cabin gardeners), Zone 4 in central Minnesota, and Zone 5a in the southern part of the state. These zones matter — a lot.

A plant that thrives in Zone 5 may not survive a Zone 3 winter, no matter how well you care for it. Before you fall in love with a plant, check its hardiness zone. At Sunnyside Gardens, our in-store plant signs include zone information to help you choose perennials that will come back year after year in your specific location.

2. Putting Perennials in the Wrong Spot

Sun-loving perennials won’t bloom in shade. Shade plants will scorch and struggle in full sun. It sounds simple, but placing plants in the wrong light conditions is one of the most common mistakes gardeners make.

Pay attention to your garden’s light patterns throughout the day. Full sun means 6+ hours of direct sunlight. Part shade means 3-6 hours. Full shade means less than 3 hours. Match your plants to the conditions, not the other way around. Our in-store signs and staff are always happy to help you find the right plant for the right spot.

Gardens aren’t static — they evolve. If you lose a shade tree or watch one grow to shade what used to be a sunny spot, don’t be afraid to move your perennials. Fall and early spring are ideal times to transplant and give your plants the light conditions they need to thrive.

3. Forgetting to Plan for Color Throughout the Season

A garden that blooms all at once in June and then goes quiet for the rest of summer is a missed opportunity. The key to a beautiful perennial garden is succession planting — choosing plants that bloom at different times so there’s always something in flower.

At Sunnyside Gardens, our plant signs include bloom times so you can plan a garden with color from spring through fall. Aim for a mix of early bloomers (like creeping phlox and bleeding heart), mid-season favorites (like coneflowers and daylilies), and late-season stars (like asters and sedum).

4. Pruning at the Wrong Time

Deadheading spent blooms can encourage more flowers and keep plants looking tidy — but pruning at the wrong time can reduce blooms or even harm the plant’s health.

Some perennials, like lilacs and peonies, set their buds the year before they bloom. Prune them at the wrong time, and you’ll cut off next year’s flowers. Others, like coneflowers and black-eyed Susans, benefit from being left standing through winter to feed birds and provide structure.

Not sure when to prune? Check out our pruning schedule for a foolproof guide to keeping your perennials healthy and blooming.

5. Spacing Plants Too Close (or Too Far Apart)

It’s tempting to plant perennials close together for instant fullness — but crowding plants can lead to poor air circulation, increased disease, and competition for water and nutrients.

On the flip side, spacing plants too far apart leaves gaps that take years to fill and invites weeds to move in.

The solution? Pay attention to the mature size listed on our in-store plant signs and space accordingly. A plant that’s 6 inches tall now may spread to 2 feet wide at maturity. Give it room to breathe.

6. Ignoring Plant Height and Layering

A flat garden is a boring garden. The most visually interesting perennial beds have variety in height, creating depth and layers that draw the eye.

A good rule of thumb: place tall plants in the back (or center, if the bed is viewed from all sides) and work your way forward to the shortest plants in front. This creates a cascading, tiered effect that feels full and intentional.

And don’t forget to stake tall plants like peonies, delphiniums, and tall phlox. A heavy rain or strong wind can flatten an entire bed of unsupported blooms — a heartbreaking and avoidable mistake.

7. Skipping the Mulch

Mulch isn’t just decorative — it’s essential. A 3-inch layer of mulch helps retain soil moisture, suppress weeds, regulate soil temperature, and give your garden beds a polished, finished look.

Without mulch, you’ll spend more time watering and weeding, and your plants will be more vulnerable to stress during heat waves and dry spells. It’s a simple step that makes a huge difference all season long.

8. Planting Too Early (or Too Late)

As long as the ground is workable, you can plant hardy perennials, trees, and shrubs. Many garden centers in Minnesota, including Sunnyside Gardens, begin carrying and selling these plants around Earth Week in late April. The early-May frost-free date matters most for annuals and tropical plants, which are sensitive to cold.

On the other end of the season, planting too late doesn’t give perennials enough time to establish roots before winter sets in, leaving them vulnerable to freeze-thaw cycles and heaving.

The sweet spot? Late April through October is the best planting window for perennials in Minnesota. Plant during this period, water well, and your perennials will have the time they need to settle in and thrive.

A Little Planning Goes a Long Way

Perennial gardening is one of the most rewarding ways to create beauty that lasts. With a little attention to zones, light, spacing, and timing, you can avoid these common mistakes and build a garden that gets better every year.

At Sunnyside Gardens, we’re here to help you plan, plant, and maintain a perennial garden that thrives. Stop by, ask questions, and let us help you grow something beautiful.