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September gardening tips: planting bulbs and trees plus houseplant savvy | The Old Farmer's Almanac

September Gardening Tips

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What to Do in the Garden in September

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After Labor Day, I can feel and see the slowing of photosynthesis as plants wind down their season. September’s silent song drives me to do things fast, before the frosts of fall. Here are some key gardening tasks to do this month!

Order Spring-Flowering Bulbs

Buy or order bulbs now for the best selection. You can plant daffodils, hyacinths, lilies and tulips up until the ground freezes solid in late fall. Here’s a list of spring-blooming bulbs to plant in fall.

If you can dig a 6-inch-deep hole, you can plant bulbs! Last year, I found tulips bulbs I forgot to plant and was able to get them in the ground even after Christmas, despite a foot of snow. They bloomed this spring.

My favorite early daffodil is ‘Tet a Tet’, from Brent & Becky’s Bulbs. Photo by Doreen G. Howard

Speaking of bulbs, don’t forget about garlic! Fall is the time to plant those garlic cloves. Read all about planting garlic here.

Select Your Trees and Shrubs

Are you thinking about planting shrubs or trees? Here in Illinois, fall planting is September through mid-October. Wherever you live, wait until the temperatures are moderate to cool because it’s easier on the plants so there is less chance for the trees to be stressed by extreme heat. When the air temperatures are cooler than the soil, new root growth is encouraged without new top growth. The result is a stronger, better developed root system for the next spring when the plant begins to grow. Mulching with wood chips helps to retain the soil’s required moisture.

Trees that can be successfully planted in the fall include alder, ash, buckeye, catalpa, crabapple, hackberry, hawthorn, honey locust, elm, Kentucky coffee tree, linden, maple, sycamore, pines, and spruces. Most deciduous shrubs can easily be planted in fall. Here’s a list of six of our favorite shrubs that offer brilliant fall color!

Some slow-to-establish species are best planted in spring, however. These include bald cypress, American hornbeam, ginkgo, larch, magnolia, hemlock, sweetgum, tuliptree, and willow. Also, broadleaved evergreens such as rhododendrons and narrow-leafed evergreens such as yews prefer spring planting. In general, plants with shallow, fibrous root systems can be planted easier in the fall than those with fewer, larger roots.

Here are a few tree-planting factors to consider:

  1. Identify the right tree: do you want shade, quick growth, color, screening or fragrance? Determine what type of soil you have. Wet or dry areas are better for different species.
  2. Find the right place for the tree: look at how much sunlight the site receives.  Most trees like full sunlight, but many need shade.  Make sure the tree is away from above ground hazards like electrical wires, underground hazards like sewer pipes and far enough away from the permanent structures (sheds, fences, etc.). Make sure the tree will have plenty of space to grow ten, 20 or even 30 years from now.
  3. Proper planting methods: dig a hole four to five times the width of the root ball. Plant so the tree trunk is 1/2 inch higher than the ground around it to prevent water from collecting next to the base of the trunk, which causes rot.  Water is important, though. Newly planted trees, unless it rains, need to be watered 20 to 30 minutes a day until the ground freezes. This helps the tree establish a root system in a short time. After planting, mulch with one to three inches of shredded hardwood or leaves. Keep mulch an inch or two away from the tree trunk to avoid rot.

These trees that offer screening and color are nearly 30 years old.  Spacing is important when you plant.  Photo by Doreen G. Howard

Be Houseplant Savvy

When cooler nights start to approach, remember that houseplants need to move inside!  A general rule is to move them when temperatures shift below 60 degrees F. Only the healthiest of plants will survive inside, so look over your pots carefully. Also, make sure you clean the pots and check for insect pests. One trick is to soak the pot for 15 minutes in a tub of lukewarm water. If there are unwanted pests hiding in the soil, they will come to the surface. If you see an entire colony emerge, it’s time to re-pot! It’s also prudent to spray the foliage with insecticidal soap a few days before you bring the plant inside. You do not want spider mites or other pests in your home.

Remember that the winter home is often a shock:

  • Heating makes our indoor air drier, warmer, and less humid. It’s often best to group plants together to increase relative humidity. When you bring plants inside, avoid drafty areas, too.
  • Plants that need full sun should be placed near south-facing windows. Plants that prefer partial sun should be placed in an east- or west-facing window.
  • Keep in mind that some plants will lose leaves when first moved indoors due to stress; they will generally recover and replace their dropped leaves.
  • Avoid overwatering once indoors; wait until the soil is dry to the touch.

National Indoor Plant Week is usually the third week in September, with good reason. Now is the time to look for houseplants at garden centers!

Peace lilies need little light and are easy to grow. Photo courtesy of Costa Farm 

Of course, September is time to start thinking about garden cleanup, too, to prepare for a better start to spring. See 10 fall cleanup tips.

Want more tips? Check our Monthly Gardening Tips by Region.

2023 Almanac Club