September Gardening Guide for Chicagoland
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Time to read 5 min
In september, summer color may still be going strong, but cooler days signal that it is time to prepare plants, lawns, and landscapes for the colder months ahead. The good news is that fall is not the end of gardening season, it is the foundation for next year’s success.
Moderate temperatures make September an excellent time to plant many perennials, shrubs, and trees, care for the lawn, address weeds, and complete important garden maintenance. Because fall weather on Chicago’s North Shore can vary significantly from year to year, successful September gardening is less about following an exact date and more about watching temperatures and understanding what your plants need. Here is your September gardening checklist for a healthier landscape this fall, winter, and next spring.
September Planting and Pruning Deadlines
The first frost is an important milestone for fall gardening. While historical frost dates provide a useful guideline, Chicagoland has experienced increasingly variable fall weather. We estimate the first frost to be in early October, but in recent years, the frost date has been in November. That makes checking your local forecast especially important when deciding when to plant, prune, and winterize.
As a general guideline, aim to complete planting of perennials, shrubs, and trees at least six weeks before the first frost so they have adequate time for roots to establish before winter.
Be Strategic About Fall Pruning
September gardening often inspires a general cleanup, but not every shrub should be pruned in fall. Light shaping and removal of dead, diseased, or damaged wood can be completed where appropriate, but be especially careful with shrubs that bloom on old wood.
These plants develop next year’s flower buds on stems from the previous growing season. Pruning them in late summer or fall can remove those buds and reduce next spring’s blooms. Avoid fall pruning of:
Bigleaf, oakleaf, mountain, and climbing hydrangeas
Rhododendrons and azaleas
Lilacs and forsythia
Many viburnums
Weigela
Instead, prune these spring-flowering shrubs shortly after they finish blooming. When in doubt, identify when and how a shrub flowers before reaching for the pruners. A little patience in September can preserve an entire season of blooms next year.
What to Plant in September
September’s moderate soil and air temperatures create favorable conditions for establishing many plants. Your September planting list can include:
Cool-season vegetables such as kale, lettuce, radishes, spinach, and turnips
Perennials, shrubs, and appropriate trees
Fall annuals and seasonal accents for continued color
Trees well suited to fall planting can include alder, buckeye, catalpa, crabapple, hackberry, hawthorn, honey locust, elm, Kentucky coffee tree, linden, maple, sycamore, pine, and spruce. Try to wrap up major perennial, shrub, and tree planting by the end of September when possible. This gives new additions valuable time to begin establishing before winter arrives.
Master Fall Fertilization
Fertilizing is one area where September gardening requires a more thoughtful approach. Different plants have different nutritional needs as they begin preparing for dormancy. Feeding certain plants too late can encourage tender new growth that is more susceptible to cold damage. For others, fall is an important opportunity to support roots and prepare for the next growing season.
Use these general guidelines:
Annuals: Continue feeding while plants are actively growing and flowering.
Perennials and roses: Stop feeding by late August or early September to avoid encouraging tender new growth.
Evergreens: If needed, use a lighter application early in fall and avoid high-nitrogen fertilizer late in the season.
Lawns: Apply an appropriate fall winterizer several weeks before the ground freezes.
Deciduous trees and shrubs: Wait until later in fall, after leaf drop, if fertilization is needed.
For established trees and shrubs, good soil health should remain the priority. A yearly layer of compost or leaf mulch can support soil structure and plant health. Synthetic fertilizer is best used thoughtfully, particularly when addressing a known nutrient deficiency.
Give Your Lawn Some Fall Attention
September is an important month for cool-season lawns throughout the North Shore and Chicagoland. Mid-August through late September is generally an ideal window for core aeration and overseeding. Cooler air temperatures combined with warm soil create favorable conditions for grass seed germination and establishment.
Fall is also an excellent time to tackle perennial weeds. As these weeds begin moving nutrients into their roots for winter storage, timely control can help reduce their return. A fall lawn winterizer can also be applied several weeks before the ground freezes to support the lawn as it heads into dormancy and prepares for spring.
The result of good September lawn care may not be immediately dramatic, but the payoff becomes much more visible when the grass begins growing again next year.
Wait for Cooler Temperatures Before These Tasks
Spring bulbs: Purchase tulips, daffodils, alliums, and crocuses early for the best selection, but wait to plant until temperatures are consistently cooler. Store bulbs in a cool, dry, dark location until planting conditions arrive.
Dividing and sowing: Wait for cooler temperatures before dividing certain herbaceous perennials or directly sowing seeds that require cold stratification.
Irrigation winterization: Do not shut down irrigation simply because September has arrived. Plants still require water during warm, dry stretches. At the same time, irrigation systems should be winterized before freezing temperatures create a risk of damage.
Watching the forecast is more useful than relying solely on the calendar.
September Gardening Is an Investment in Spring
September may feel like the garden is beginning to wind down, but below the surface, important work is still happening. Roots are establishing, lawns are recovering from summer stress, trees and shrubs are preparing for dormancy, and gardeners have an opportunity to address issues before winter arrives.
Think of September gardening as an investment in your future garden. Plant at the right time, prune selectively, support healthy soil, care for your lawn, continue watering when necessary, and resist the urge to winterize too soon. For North Shore gardeners, following the weather is particularly important. A warm September or October can extend the season considerably, while an early cold snap can quickly shorten your planting window.
Visit our store Chalet Home + Garden and our horticultural experts can help you navigate fall planting, lawn care, pruning, soil care, spring bulbs, and the other seasonal tasks that prepare Chicagoland gardens for the months ahead.
Is September a good time to plant in Chicagoland?
Yes. September’s moderate temperatures can make it an excellent time to establish many perennials, shrubs, and trees. Plant early enough to provide roots with time to establish before winter.
Should I prune shrubs in September?
It depends on the plant. Dead, damaged, or diseased growth may be addressed where appropriate, but avoid fall pruning of spring-flowering shrubs that bloom on old wood, including lilacs, forsythia, and certain hydrangeas.
Should I fertilize my garden in September?
Not everything should be fertilized at the same time. Perennials and roses should generally stop receiving fertilizer by late August or early September, while lawn and woody plant fertilization follows different seasonal timing.
When should I plant tulip and daffodil bulbs?
Shop early for the best selection, but wait for consistently cooler temperatures before planting spring-flowering bulbs. Tulips, daffodils, alliums, and crocuses can be stored in a cool, dry, dark location until planting time.
When should I winterize my irrigation system?
Do not winterize too early if warm weather continues and plants still need water. Watch nighttime temperatures closely and schedule winterization before hard freezes can damage irrigation components.
Chris Hester
Chalet Home + Garden
