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Fall Gardening: September Garden Checklist Zones 4-5

As summer wanes, September brings brisk mornings, crisp cool air, and trees that begin to change their hues to put on a fall show. There is still some life in your September garden as you continue to harvest, plant, and maintain the landscape.

Not sure what you should be doing in the garden this month? Extend your harvest and keep your gardens in tip-top shape with some tips from our September Garden Checklist Zones 4-5.

Chrysanthemums bloom in the autumn garden.

September Garden Planning Checklist

As we round out the summer gardening season, you probably have a lot to reflect on. As gardeners, it’s essential to acknowledge what gave us the most pride as growers and what may not have gone as anticipated.

Perhaps you had a tremendous tomato crop, have a prize-winning pumpkin still clinging to the vine, or maybe you had such a plentiful harvest that you were able to contribute your surplus to the local food bank. Or perhaps a storm came through and bent your tomato plants, garden pests munched on your crops, or your lilacs didn’t bloom as you’d hoped.

September is a great month for reflection, troubleshooting, and planning to help you bolster your future gardens and prepare for the upcoming chill.

  • Walk around your September Garden with your garden journal and make a note of high-performing and underwhelming plant varieties. If you had some favorite star performers, add them to your list to buy seeds or plants for next year.
  • Plan to harvest your own seeds from your garden this month. This is an exciting and rewarding task, and you’ll be grateful that you did when it comes to next year’s garden.
  • Make some notes in your garden journal about the weather and how it impacted your garden this year. Were there any significant storms, droughts, or excessive rains?
  • Jot down what pests were a problem for you this year and when they popped up
  • Identify which spring flower bulbs you’d like to plant this fall and purchase them from garden centers this month when the bulb selection is most plentiful.
  • Recently, there has been a rise in self-sustainability, and some seeds have been hard to come by. Think about what seeds you’d like to acquire for spring and make your purchases now.
  • Sketch and/or photograph your vegetable garden layouts and keep them in your garden journal. This way, you will know how to rotate your crops for next year.
  • As summer gardens begin to die back, consider ways to add color and draw beneficial insects to your fall gardens. Consider planting nasturtiums, marigolds, asters, cosmos, mums, and anemones.
  • It’s time to shift gears and plant your fall planters with eye-catching annuals. Summer blooms are fading, but there are many opportunities to add color and visual interest to your fall landscape. Try pairing some fall showstoppers like heuchera, mums, asters, ornamental cabbage, and variegated ivy.
  • Make a note of any diseased or spotty plants and remove them from your garden. Include the variety of plants and where it was planted, and discard the debris far away from your garden or compost pile.
  • If you are planting a cover crop this fall, acquire the seeds for planting and get started this month.
  • The cooler days of September are a great reminder to prep for frosts and colder weather. Think about season-extending tools like hoop-houses, cold frames, and greenhouses. Construct or purchase materials to make fall and winter gardens a reality. You can also stock up on row covers to protect crops from upcoming frosts.
  • Assess your yard and garden for anything that needs repair or change. Would you like to start a compost area? Does a fence need repair?  Does your vegetable garden need more secure fencing? Would you like to build raised beds or build some climbing structures? Write down any materials that you might need for these projects.
  • Check back to your gardening wish list in your garden journal for any items that may be on clearance racks at the end of the summer season. Now is a great time to pick them up at a discount.
  • Consider what new perennials and shrubs you’d like to add to your landscape. Early fall is an excellent time for planting.
  • Are your seed packets in a jumbled mess after this summer of vigorous planting? Consider ordering some seed organizing supplies and write this down as a late fall or winter task.

Fall Garden Prep & Maintenance

September is a big month for prep and maintenance for just about all gardeners. Some of these garden to-dos may seem redundant, but if you keep up with them from month to month, your future gardening seasons will be less arduous. Not sure what you should be doing in the September Garden?  Here are some key tasks to get you started.

Weeding the Garden in September

Keep up with the weeds as you see them throughout the month of September. You may be tempted to let them be and have future frosts kill them off. Avoid this methodology because you don’t want those weeds to go to seed and be even more of a problem next year.

Fall Mulching

Mulching remains a high priority on the September garden checklist Zones 4-5 because it is so beneficial to gardens. Continue to mulch your September garden beds. Here’s why:

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  • It gives the yard and garden a fresh look.
  • Mulch enriches the soil over time as it breaks down.
  • Mulch stomps out those fall weeds.
  • Prevents soil erosion from heavy rains, winds, and storms.
  • Retains moisture during bouts of drier weather.
  • Insulates bulbs, perennial root systems for the upcoming cold weather.
Phlox and Hostas flowers in the garden

Late Summer Watering

Watering is vital to help new perennials and trees establish their root systems and for those already set plant root systems to stay adequately hydrated.

Conversely, annual plantings are slowing down a bit in their growth, and cooler temperatures may mean they don’t need as much water as they did during the peak of summer. You can also stop watering deciduous trees as their foliage is transitioning this month.

When & What to Fertilize in Zones 4-5

  • Stop fertilizing trees and shrubs if you haven’t done so already. Cooler weather is approaching, and new growth established from fertilization can cause those limbs to be susceptible to damage.
  • Fertilize vegetable gardens as needed. This includes gardens that include summer vegetable plants that are still producing, fall vegetable gardens, and gardens that have finished producing. Organic fertilizers help build the soil and take time to break down to be available to plants for the next growing season.
  • If you have a cool-season lawn variety, it’s time to fertilize your lawn. If you are unsure what kind of grass that you have, bring a small clump to your local extension office and ask for some guidance.

September Garden Pruning

  • Stop pruning trees and shrubs in your September Garden. Cooler weather and frosts can cause new growth to be susceptible to damage.
  • Remove some foliage from pumpkin plants to allow fruits to ripen.
  • Remove any female flowers or immature fruits from squash, tomato, melons, pumpkins, and eggplants as they have little chance of maturing at this point in the season. Pinching them off will push the energy to fruits that are already established.
  • Allow perennial plants to die back before cutting them back. Allow some seed heads to remain on plants for birds to feed on and for seed collection.
farmer examining growth quality of sunflower seeds.

Other Garden Tasks on September Garden Checklist Zones 4-5

  • It’s a great time to divide perennials like hostas, daylilies, rudbeckia, Shasta daisies, etc.
  • Plant new hardy perennial plants in the cooler days of September. This gives plenty of time for roots to get established before winter sets in.
  • Dig up tubers of gladiolus, dahlias, cannas, and caladiums and store them in dry peat moss over the winter.
  • Bring in any houseplants that you’ve had outside this summer. This includes potted citrus trees.
  • Tidy up your garden landscape, picking up any dried foliage, dropped fruit, or dropped leaves.
  • If you’ve been growing any tropical plants, start transitioning them indoors. They need to adjust to the change in lighting conditions gradually to prevent leaf drop.
  • Start assembling your fall containers. Create an eye-catching pop of color and textural intrigue.
  • Collect seeds from high-performing plants and store them in seed collection envelopes. Don’t forget to label them.
  • Plant your spring bulbs.
  • Turn your compost pile with a pitchfork. Remember not to place any diseased foliage into your compost heap.

Outdoor Planting in September

  • Sow a succession crop of lettuces, radishes, spinach, carrots, and kale in cold frames, greenhouses, and hoop houses. Have row covers ready for upcoming frosts in planting in a traditional garden bed.
  • Plant garlic and shallots.

Late Summer Harvesting

Those in Zones 4-5 can continue harvesting all crops that continue to produce in the vegetable garden. It’s also apple picking time! Harvest your vegetable garden before the danger of frost or in order to make room for your fall plantings. Discard healthy spent leaves and plants into your compost pile.


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kale plants growing in a garden
dahlia flowers in a vase

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