September can still be a busy month in the yard.

Around Mukwonago and Waukesha County, we can have warm, summerlike days well into the month, followed by cool nights that suddenly make fall feel very close.

The important thing is not to treat September like the season is over.

Your trees, shrubs, perennials, annuals and containers are still growing, still using water and, in many cases, still giving you plenty to enjoy.

For most southeast Wisconsin yards and gardens, September is a good month to focus on a few things:

• Keep an eye on soil moisture.
• Give anything planted this year a little extra attention.
• Plant trees, shrubs and perennials when the timing is right.
• Keep healthy flowers and containers going.
• Remove diseased or truly finished plant material.
• Take a good look at your trees, but don’t rush into major pruning.
• Start getting spring-blooming bulbs into the ground as the soil cools.

You don’t need to do everything at once.

Keep Watering When Plants Need It

A few cool mornings can make it easy to forget about watering.

Don’t.

Trees, shrubs and perennials planted this year are still establishing roots. Evergreens need good moisture going into winter. Containers can dry out surprisingly fast, even when the weather feels cooler.

The best thing you can do is check the soil instead of watering by the calendar.

How to Check the Soil

Don’t go by how the surface looks. The top inch may be dry while the soil around the roots is still moist.

For annuals and smaller perennials, use your finger or a small trowel and check a few inches down.

For shrubs and larger plants, a long screwdriver can give you a good idea of how dry the soil is farther down. If you want a more exact reading, use a soil probe to check deeper in the root zone.

If you have mulch, move it aside first.

What you’re looking for is simple:

• Cool and moist? You can probably wait.
• Dry and crumbly? It’s time to water.
• Soggy? Leave it alone.

UW–Madison Extension recommends checking soil moisture and continuing to water landscape plants as needed into fall, especially newer plantings and evergreens.

UW–Madison Extension: Drought and Watering of Ornamental Plants

Water Deeply

When you do water, give the roots a good drink.

A light sprinkle over the top of the soil doesn’t do much for a tree or shrub. Water slowly enough that it can soak into the root zone instead of running off.

Soaker hoses can work very well in larger beds.

And remember: rain counts. If we’ve had a good soaking rain, check before adding more.

September Can Be a Great Time to Plant

September is one of our favorite months for planting many things.

The air is usually cooler, the soil is still warm and plants aren’t dealing with the same kind of stress they can experience during July heat.

That doesn’t mean every plant belongs in the ground in September.

Some trees and shrubs are very good fall candidates. Others are better planted in spring. Evergreens need enough time to establish before winter, so earlier fall planting is better for them.

UW–Madison Extension recommends September into early October, weather permitting, for fall planting of a number of deciduous trees and shrubs.

UW–Madison Extension: Tree Species Recommended for Fall Planting

Before choosing a tree or shrub, think about the spot first.

How much sun does it get?

Does the soil stay wet after a heavy rain?

How much room will the plant have when it’s mature?

Is the area exposed to winter wind?

Those details matter.

If you’re planning a fall project, take a look at our Trees and Shrubs pages, then come in and tell us a little about the space you’re working with.

Keep Enjoying Your Flowers

If your annuals still look good, leave them alone and enjoy them.

There is no reason to pull healthy flowers simply because September arrived.

Keep watering them as needed and let frost decide when their season is finished.

Containers need the same attention. They can dry out faster than garden beds because there is less soil around the roots.

September is also when some of our favorite late-blooming perennials start showing off.

Asters, goldenrods, sedums, coneflowers and other fall bloomers add color at a time when the garden can really use it. They also provide important nectar for bees, monarch butterflies and other pollinators that are still active.

UW–Madison Extension: Fall Flowers Fuel Monarch Flights

You can also browse our Flowers, Annual Flowers and Native Wisconsin Plants pages for ideas.

Don’t Cut Everything Down

September is not the month to clear every bed down to bare soil.

Start with the things that really should go:

• Diseased foliage.
• Rotting or badly damaged plant material.
• Annuals that are clearly finished.
• Weeds before they drop more seed.
• Spent vegetable plants, especially if they had disease problems.

Healthy perennial stems and seed heads can often stay.

They can provide winter interest, seeds for birds and shelter for beneficial insects.

Some plants do have specific fall-care needs, so don’t assume every perennial gets treated the same way.

Before you cut something back, ask yourself why you’re doing it.

If there’s no good reason, it may be better to leave it alone.

We’ll talk more about that in September Flower & Perennial Care in Southeast Wisconsin.

Look at Your Trees, But Don’t Rush to Prune

September is a good month to take a slow walk around the yard and really look at your trees.

Check for:

• Dead or broken branches.
• Storm damage.
• Branches rubbing together.
• Cracks.
• Changes in bark.
• Limbs that may eventually interfere with a building or walkway.

What you generally don’t want to do is start major routine pruning just because fall is coming.

For many deciduous trees in southeast Wisconsin, dormant-season pruning is the better choice.

Dead, broken or hazardous branches are different. Those can be dealt with when needed.

If you’re wondering what should come off and when, we have a complete guide for that:

Best Practices for Pruning Trees in Southeast Wisconsin

Start Thinking About Spring Bulbs

September is also the time to start planning for next spring.

Tulips, daffodils, crocus, grape hyacinths and other spring-blooming bulbs need a cold period before they’ll bloom.

You don’t need to panic if you haven’t planted them on September 1. Fall bulb planting can continue as the soil cools and before the ground freezes.

Good drainage matters, and planting depth depends on the bulb, so follow the recommendation for the variety you’re planting.

One other thing to remember: look at the yard the way it will look in spring.

A spot under a deciduous tree may seem shady in September but get plenty of sun before that tree leafs out next spring.

UW–Madison Extension: Planting Spring Bulbs

Pay Extra Attention to Anything You Planted This Year

If you planted it this spring or summer, keep watching it.

That includes:

• Trees.
• Shrubs.
• Perennials.
• Plants you’ve moved or divided.
• New garden beds.

These plants haven’t had years to build a big root system yet.

They may look perfectly fine above ground and still be too dry underneath.

Evergreens deserve special attention because they continue losing moisture through their foliage in winter. If they go into winter dry, they are more likely to show winter burn later.

UW–Madison Extension: Keep Watering in Fall to Protect Evergreens from Winter Burn

What Really Needs to Get Done in September?

If you only remember a few things, make it these:

1. Check the soil before you water.
2. Keep a close eye on anything planted this year.
3. Plant when the plant and timing are right.
4. Keep enjoying healthy annuals and fall flowers.
5. Remove problems, not every plant in the bed.
6. Look over your trees and save most routine pruning for the right time.
7. Plant spring bulbs as the soil cools.

That’s enough.

September is less about putting the yard to bed and more about helping what you already have finish the season well.

September Yard & Garden Questions

Should I stop watering in September?

No. Check the soil and water when it needs it. Newly planted trees, shrubs and perennials, along with evergreens, deserve extra attention.

Is September too late to plant in southeast Wisconsin?

No. September can be a very good planting month for many trees, shrubs and perennials. What you’re planting matters, though, and some plants are better planted in spring.

Should I cut all my perennials back?

No. Remove diseased or badly damaged material, but many healthy stems and seed heads can stay through winter.

Should I prune my trees in September?

Usually not for routine or major pruning. September is a good time to inspect your trees and make a plan. For most deciduous trees, dormant-season pruning is a better choice.

Read our Best Practices for Pruning Trees in Southeast Wisconsin.

Can I plant spring bulbs after September?

Yes. In southeast Wisconsin, bulb planting can continue later into fall as long as the soil is workable and you’re ahead of a hard freeze.

Have a Question About Your Yard?

Bring us some photos.

If you’re concerned about a plant, take one photo of the whole plant, one showing where it’s growing and a close-up of whatever you’re seeing.

If you’re choosing something new, a photo of the space helps too.

We’ll help you figure out what makes sense for your yard, your plants and southeast Wisconsin conditions.

Thomas Greenhouse & Gardens
420 Maple Avenue
Mukwonago, Wisconsin

Sources & Further Reading

Research-based horticultural guidance used in this article:

• UW–Madison Extension: Drought and Watering of Ornamental Plants
• UW–Madison Extension: Tree Species Recommended for Fall Planting
• UW–Madison Extension: Fall Flowers Fuel Monarch Flights
• UW–Madison Extension: Planting Spring Bulbs
• UW–Madison Extension: Keep Watering in Fall to Protect Evergreens from Winter Burn