As summer’s heat gives way to cooler nights and the first hints of autumn, September in Southeastern Wisconsin is a pivotal month in the garden. You’re juggling the final harvest of warm-season crops with planting and prepping for fall and even spring blooms next year. Here are five essential tips—tailored to Zone 5’s climate—to help you make the most of this transitional month.
1. Adjust Watering and Refresh Mulch
- Scale back irrigation gradually. With cooler overnight temperatures and occasional rain, reduce supplemental watering to about ¾ inch per week. Early-morning watering remains best to minimize fungal issues.
- Top up mulch layers. A fresh 2- to 3-inch layer of organic mulch (shredded bark, leaf mold, or straw) conserves moisture, insulates roots, and keeps weeds at bay as temperatures fluctuate.
- Watch container plantings. Pots and hanging baskets dry out faster as days shorten—check them every other day, and consider adding water-retaining crystals or switching to thicker-walled containers.
2. Plant Fall Crops and Cover Crops
- Direct-seed cool-season vegetables such as:
- Leafy greens: Spinach, arugula, and lettuce varieties that bolt slowly in cooler air.
- Roots: Radishes, beets, and carrots—thin seedlings as they emerge to 2–3″ apart.
- Transplant hardy starts of kale, broccoli, and cabbage in early September to give them time to establish before frost.
- Sow cover crops (winter rye, clover, or hairy vetch) in bare beds by mid-month. They protect soil structure, suppress weeds, and add organic matter come spring.
3. Lawn Care: Aeration, Overseeding, and Feeding
- Core-aerate compacted turf to improve oxygen, water, and nutrient penetration. Early September is ideal for strong seedling establishment.
- Overseed bare or thinning patches with a cool-season grass mix formulated for full sun or shade, depending on your lawn.
- Apply a fall fertilizer high in phosphorus and potassium to strengthen roots and help grass recover from summer stress. Aim for a slow-release formula in mid-September.
4. Clean-Up and Disease Management
- Remove spent annuals and diseased foliage from vegetables and ornamentals. Compost only healthy debris; discard any material showing signs of blight or mildew.
- Rake fallen leaves regularly. While a light mulch of leaves can insulate perennials, a thick mat can smother turf and encourage slugs and fungus.
- Sanitize tools between uses—especially after cutting back tomatoes or squash—to prevent pathogen spread. A 10% bleach solution or 70% isopropyl alcohol works well.
5. Spring Bulbs and Perennial Division
- Plant spring-flowering bulbs (tulips, daffodils, crocus) between late September and early October. Ensure good drainage by mixing in bulb-planting mix or compost.
- Divide overgrown perennials such as daylilies, hostas, and iris. Lift clumps, separate into smaller sections with healthy shoots and roots, then replant and water in well.
- Feed divisions and new bulbs with a balanced, low-nitrogen bulb food to jump-start root growth before the ground freezes.
Ready for What’s Next?
By following these September gardening steps—adjusting water, seeding for fall, caring for lawns, managing cleanup, and planting bulbs—you’ll bridge the gap between summer’s end and a vibrant spring ahead.
Stop by Heritage Hill Nursery for all your cool-season seedlings, bulbs, soil amendments, and expert advice. You can also browse online at heritagehillnurseryinc.com.
Here’s to a productive September and a garden that shines through every season!