September Gardening To-Do List


  1. Harvest - September is often the big harvest time for tomatoes, peppers, and hot season vegetables.
  2. Plant Cool Season Annuals - Plant cool season annuals and ornamentals such as pansies, violas, snapdragons and ornamental cabbage. 
  3. Plant Cool Season Vegetables - You still have time to plant peas, broccoli, cauliflower, kale, brussel sprouts, leeks, lettuce, radish and onion.  You may have to cover them for frost if you don’t have a cold frame, but if you get them in right away you should get a harvest if a freeze isn’t early. 
  4. Pick Up Wasp Spray - Wasps and yellow jackets become a problem this month.  Be prepared with sprays. 
  5. Feed Annuals - Annuals need regular fertilizing for good bloom production, about every 4 weeks with Espoma granulars but every 8 weeks with Dr, Earth granular fertilizers 
  6. Check Containers and Baskets - Container gardens, hanging baskets and window boxes dry out quickly and need frequent watering.  They will also need to be fertilized regularly. 
  7. Lower the Blade - You can begin lowering the blade on the lawn mower as temperatures cool.  Lower slightly next month again too until you wind up mowing quite short the last time or two. 
  8. Lawn Repair - When summer starts to cool and the soil is still good and warm, which could be early September, lawn seed will establish quickly.  If you plan to overseed the whole lawn, core-aerate first. 
  9. Divide Perennials - Perennials that are done blooming may be divided and/or moved.  The roots will have time to reestablish before frost.  Don’t divide or move plants that thrive in fall, such as asters, mums, Russian sage and ornamental grass. 
  10. Fertilize the Lawn - Apply a winterizing fertilizer later in the month, a lower nitrogen and higher potassium formula such as 18-0-12 ratio, to strengthen the lawn before winter without encouraging fast growth. 
  11. Core Aerate the lawn every few years in September.  
  12. Water - Plants, shrubs, trees will need regular watering right up until frost, and diminished rainfall in autumn isn’t enough.  Evergreens especially need lots of water to prepare for winter since they keep their needles green all winter.  To prevent needle drop and burn, make sure they get plenty of water right up until the ground freezes if you can. Apply broadleaf weed control  Fall brings a fresh crop of lawn weeds.  
  13. Apply broadleaf weed control early in September.  Although you can purchase fertilizer with broad leaf weed control, conditions should be ideal when you apply (read the package) for best results.  Mixing up some weed killer in a tank sprayer is more effective.  It also allows you to spot spray individual weeds and target small areas.  Clover and creeping charlie require several applications.  With a pump sprayer you can target those every 2 weeks.  DO NOT spray young grass seedlings. 
  14. Remove Dead Plants - Shrubs, perennials or trees that have died should be removed. 
  15. Clean Up Fruit - Clean up and remove any fallen fruit.  Decaying fruit will harbor pests and disease. 
  16. Slugs are Active - September brings slugs out in full force. Apply Sluggo with Iron Phosphate as the active ingredient. 
  17. Fill in with CompostAs you clean out the garden beds, fill in with compost so the soil is ready in spring. 
  18. Check for Web Worms - Prune the web out of the trees if possible and destroy.  Otherwise treat chemically. 
  19. Be Prepared to Lift Bulbs - Tender bulbs should be lifted and stored next month.  But if winter is coming early, you may need to get it done at the end of this month. 
  20. Needle Drop - Don’t be alarmed to see your evergreen drop some needles.  Old inner needles will drop in Fall because new needles formed on the branch tips. 
  21. Plant Perennials - September is an excellent time to plant perennials.  Days are warm and nights are cool, perfect for establishing roots. 
  22. Plant Fall Bloomers - You can still pick up mums and asters in bloom for planting right now. 
  23. Plant Peonies - Plant, or divide and transplant peonies between the end of August and October.  September is usually perfect.  Remember that peonies prefer not to be disturbed, so divide only if the clump has gotten way too large or needs to be in more sun. 
  24. Plant Bulbs - Plant spring blooming bulbs in September or early October. 
  25. Be Prepared for Frost - Zone 5 generally does not experience frost until next month, but it does happen in September occasionally.  Be prepared to cover your tender plants and crops if frost is forecast. 





Jennifer Brennan is the Horticulture Information Specialist, advising and coaching gardeners at Chalet for over 30 years.