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September feels different. The air is crisper, the light is golden, and there’s a sense of urgency beneath the calm — summer is ending, fall is arriving, and there’s a lot to do before the ground freezes.

September is one of the most rewarding months in the Minnesota garden. The heat of August is gone. The chaos of spring planting is behind you. The soil is still warm, but the air is cool and pleasant. Rainfall is consistent. Conditions are perfect for some of the most important garden work of the year.

Here’s everything you need to know to finish the growing season strong and set your garden up for a spectacular spring.

GARDEN: Preparing for the Season Ahead

Divide Perennials Now

September is ideal for dividing perennials — especially those that have become overcrowded or that bloom in spring.

Best candidates for division:

• Peonies: Late September is perfect — they need time to establish before winter
• Hostas: Divide after flowering
• Daylilies: Divide anytime
• Iris: Early September is ideal for bearded iris
• Other spring bloomers that need rejuvenation

Dividing not only rejuvenates tired plants — it gives you new plants to fill gaps or share with friends.

Final Deadheading for Another Bloom Wave

September isn’t too late to deadhead. Coreopsis, yarrow, and other bloomers will produce another wave of flowers if you remove spent blooms now.

Deadhead every few days for continuous color through September.

Leave Seed Heads Standing

Here’s what NOT to deadhead: Coneflowers, rudbeckia, monarda, sedum, and ornamental grasses. Leave their seed heads standing through fall and winter.

Why? Birds feed on the seeds. Pollinators shelter in the dried stems. The structure provides winter interest and architecture in your beds. Plus, many of these plants self-seed, helping them return fuller next year.

Cut Back the Tired

Anything that’s flopped, done blooming, or turning mushy should be cut back.

This includes:

• Smooth hydrangea: After blooms have faded
• Peonies: After foliage dies
• Daylilies: After flowering
• Allium: Spent flower heads
• Phlox: Past prime
• Iris: After blooming
• Columbine: Finished for season

Cutting back prevents disease, tidies the garden, and signals to plants that it’s time to prepare for dormancy.

Continue Weeding

Weeds are still growing in September. Pull them before they go to seed — which means preventing thousands of weeds next spring. This is preventive maintenance at its best.

Harvest Remaining Vegetables

September is harvest season for summer crops. Pick tomatoes, peppers, beans, and zucchini regularly.

For root crops, September and early October are perfect for harvesting: Potatoes, carrots, winter squash, beets. These crops actually sweeten in cool weather, so don’t rush.

Once harvested, clear the area: Pull out spent plants, remove fallen leaves, and tidy the bed. This reduces disease habitat and pest overwintering sites.

Plant Spring Bulbs Starting Mid-September

The magic window opens to plant bulbs. Starting mid-September through October, soil is warm enough for bulbs to develop roots before winter dormancy, but cool enough to prevent sprouting.

Plant these in fall:

• Tulips
• Daffodils
• Crocus
• Hyacinths
• Alliums
• Garlic

You’ll be rewarded with spring color while you’re still waiting for summer annuals to arrive.

HOME: Bringing Plants Inside

Monitor Overnight Temperatures

Start watching the overnight forecast. When temperatures consistently dip to 40–50°F at night, it’s time to bring houseplants inside. Leaving them out too long in cold temperatures causes stress and damage. Better to bring them in when nights turn cool. 

Before bringing them in, make sure to check for pests and give them some TLC. A slow transition and repot if needed will pay off with healthy growth over winter, when plants can struggle due to low light.

Style Your Indoor Plants

September is perfect for styling your indoor plant collection. New plant stands, fresh containers, or rearranging plants near windows creates visual interest while preparing for the months ahead when we have less sunlight.

Start Your Halloween Display

September is the moment to begin your seasonal transformation. Gather specialty pumpkins, gourds, fall annuals, and Halloween decor.

Style your front door. Create porch displays with container gardens. Bring out autumn colors and festive touches inside your home. Get cozy with sweaters and blankets.

Sunnyside Gardens and Trill Boutique have everything you need — from decor accents to specialty pumpkins to seasonal styling pieces.

LANDSCAPE: The Prime Planting Season

Peak Season to Plant Perennials, Shrubs & Trees

September is arguably the best time of year to plant in Minnesota.

Here’s why:

• Soil is still warm: Encouraging root development
• Air temperatures are cool: Reducing transplant stress
• Moisture is consistent: Fall rain support establishment
• Time before frost: Roots can develop for 6–8 weeks before dormancy, giving plants a head start over spring plantings.

What to plant:

• Perennials: especially late bloomers like asters and sedums
• Shrubs
• Trees
• Fill in any gaps from failed summer plantings

Plant deeply, water well, mulch after the ground cools: These plants will head into winter stronger and come back more vigorous in spring.

Prime Time for Lawn Seeding

September is Minnesota’s golden window for lawn care for all of the same reasons. It’s nearly perfect conditions for seed germination and establishment.

• Overseed thin or bare areas: Fall is a better time than spring. Fall seeding gives grass time to establish deep roots before winter.
• Apply fall fertilizer: Strengthen existing grass and prepare it for winter dormancy. This investment now pays dividends next spring.

Avoid Heavy Pruning (With Exceptions)

General rule: Don’t prune in September. Pruning stimulates new growth, which frost will kill, leaving plants damaged.

Exceptions: Remove branches that are dead, diseased, and overgrown or hazardous.

Critical Note: Dispose of diseased plant material in the trash, never in compost. Diseased debris in compost spreads problems to next year’s plantings.

Continue Watering Through Freeze

Water remains important through September and into October. New plantings and recently divided perennials especially need consistent moisture to develop strong root systems.

Water until the ground freezes: Deep watering in fall supports root development in your entire landscape — established plants and new plantings alike benefit.

The September Perspective

Every garden task feels easier in September. The air is crisp and energizing. The light is golden and forgiving. There’s time to work without summer’s heat demanding you quit by 10 AM.

So embrace the season! Pay attention to timely to do’s, take advantage of the sunshine we have left, and kick off the holiday season early. Your garden, your spirit, and your spring self — will thank you.