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Download a printable copy of our September Gardening “To-Do” Checklist.


  • September is THE month to grow grass seed!  That includes: overseeding or patching an existing lawn, and starting a new one.  Those links take you to our up-to-date, earth-friendly lawn care articles.
  • September and October are the best times to feed your lawn, and one application each month is best.  (Remember, turfgrasses need 2 pounds of Nitrogen per 1,000 square feet each year to stay thick and relatively weed-free).  You can then seed right over the fertilizer.  Click here and scroll down to Fall for details about which fertilizers to use.
  • You can also apply lime this month if a soil test indicates it’s needed.  Apply after fertilizing but before the ground freezes.

Herb Garden

  • Plant cool-season vegetable crops now – cabbage, turnips, kale, mustard, spinach, lettuce, broccoli, collards, carrots, and beets. Keep seedlings and transplants well watered and mulched.  (The seeds will need at least 2 weeks more time to grow to maturity now than they did in the spring due to reduced light.)  You can cover fall garden crops later in the month with a floating row cover or cold frame to further extend the harvest period.
  • Brassicas all taste better after they have been touched by a frost or two and if covered (even just with leaves), most vegetables will survive the winter to provide an early spring harvest.
  • Feed your fall vegetables weekly.  When feeding, it’s fine to wet the plant foliage, but be sure to soak the soil around the plant, too.
  • Garlic cloves can be planted up until Thanksgiving for harvest in June.  Choose the largest cloves from the largest heads, plant the cloves root end down, spaced 4-6 inches apart, and cover with 1-2 inches of soil.  Use your own home-grown garlic rather than store-bought, if possible.
  • Dig storage potatoes on a cloudy day after the plants begin to die back, then let them dry for a few hours before bringing them inside – but don’t wash them!  Store potatoes in a dark, cool location. Sweet potatoes should be harvested the same way, except that it’s best to cure the roots for 10-14 days in a warm, dark location and then store them for the winter in a cool, dry location.
  • Harvest your onions, once their tops have withered, by lifting the bulbs and drying them in a warm, dry, sunny location for 10 days. Then store them in a cool, dark, dry place.
  • To harvest herbs, remove individual leaves of tarragon, rosemary, basil, sage, etc.  and dry them indoors. Herb leaves are most flavorful right before the plant blooms. Snip foliage in the morning after the dew has dried. To dry herbs for storage, tie the cut stems together and hang them upside down in a dry location. Cover with a paper bag to avoid losing the shattered leaves. Store dried herbs in glass jars away from light and heat. Fresh basil can be processed into pesto or frozen in plastic containers for winter use.

Trees, Shrubs

  • September is an excellent time to plant or move trees and shrubs – just be sure to keep them watered if there isn’t sufficient rain. (Click here for more about watering new plants.)  But don’t plant when the soil is wet – it ruins the soil structure, making poorly draining clay soils even worse.  (Rain IS great for buying plants – you’ll have the store more or less to yourself with abundant staff.
  • Keep shrubs and trees watered through the first hard frost so that they can survive the winter.  Evergreens especially need to go into winter well hydrated.  They’re the plants that rarely wilt, giving us the sign that they need watering.
  • Do NOT feed or prune this month – both stimulate new growth, which wouldn’t have time to harden off before it gets really cold, and all that new growth would quickly be killed.  It’s fine, however, to remove dead, damaged, diseased branches; also, suckers and water sprouts.


  • September is a great time to plant the late-blooming perennials that will give you the last splash of color before the weather turns colder. Asters, Goldenrod, Toad Lilies, perennial Sunflowers, false Sunflowers, Japanese Anemones – these are all good choices. Make sure to water new plantings well, and continue to do so, until they go dormant for the winter. Setting them up perfectly in the beginning will ensure that the plants are healthy and strong for the coming years.
  • This month is also a good time to divide any of the spring blooming perennials that should need it such as Peonies, Creeping Phlox, Poppies, and Irises. Plants such as Hosta and Daylilies can be divided this month as well. Just as when adding new plants to your garden, you’ll want to water well after you’ve replanted the divisions and continue to water them regularly until the first frost. This will help to ensure their long-term success.
  • Perennials don’t need to be given additional fertilizer in the fall. However, it is recommended that you use a granular root stimulator, such as Espoma BioTone, when planting and dividing but anything else is unnecessary until next season.
  • September is a great time to amend the soil with some compost (LeafGro is good) or manure. The weather will be warm enough for the beneficial micro-organisms to work their way deep into the soil before the cold sets in. This will give your plants a head start for next year. Those beneficial organisms will be deep in the soil when it starts to warm up next spring and be readily available to those perennial roots deep in the ground as the plants begin to come out of dormancy.
  • Many perennials will start to look a bit tired.  You will start to notice some leaf discoloration. Hostas, for example, may start to turn golden yellow and stop putting out new leaves. This is a normal response to the sun being out for a shorter period of time, and for it being lower in the sky (that is to say, less potent).
  • Trim dead leaves and stems as you see fit but consider the wildlife when doing so. Finches love the seeds from spent coneflowers and Black-eyed Susans.       Don’t cut back ornamental grasses until late winter. Not only do the dried blades look attractive, but it makes a great cover for over-wintering birds.


  • Plant hardy mums now so they will become well established prior to cool weather.
  • Pansies, violas, ornamental cabbage and kale can also be planted this month.  More great plants for fall color include sweet alyssum and dusty miller.
  • Continue to fertilize your annuals this month – a liquid fertilizer gives them the boost they need and is fast-acting.  Espoma’s Gro Tone is one good option; it’s a fish protein-based liquid fertilizer that doesn’t smell as bad as most fish-based products.  It maximizes the annuals’ lifespan and increases their vibrancy and color.


  • Buy spring-blooming bulbs as soon as they’re in the stores for the best selection.  Select healthy, disease-free bulbs.
  • Plant spring-flowering bulbs this month or next – except for tulips, which should be planted from mid-October through November.  Add bone meal or bulb fertilizer into the planting hole as you prepare the soil.


  • September is the ideal month to bring houseplants indoors after they’ve spent the summer on your deck or patio, rather than later in the fall when the difference between outdoor and indoor temperatures would stress them unduly.  Treat houseplants with horticultural oil and neem oil to control aphids, mites, mealy bugs and scale.


  • September is when the birds start their winter migration, so it’s a good time to send them off with a full energy source.

This Post Has 3 Comments

  1. Hi,

    We met in your beautiful Christmas Shop yesterday. Everything was gorgeous. Behnke’s is my “therapy”. It was a pleasure talking to you.

    Monica Rupp

    1. Hi Libby,

      I think you mean Holly Tone. Established acid-loving plants should be fed twice yearly, spring and late fall. Use half the recommended rate in the fall.


      Larry B

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