September Zone 4

What to do in the garden in September in zone 4

Average first frost date September 15

  • Harvest  September is often the big harvest time for tomatoes, peppers, and hot season vegetables.
  • Pick up wasp spray  Wasps and yellow jackets become a problem this month.  Be prepared with sprays, but don’t bother those beneficial yellow jackets if they are not bothering you.
  • Feed annuals  Annuals need regular fertilizing for good bloom production, about every 4 weeks.
  • 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.
  • 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.
  • Lawn repair  When summer starts to cool and the soil is still good and warm, which could be mid August or early September, lawn seed or sod will establish quickly.  If you plant to over seed the whole lawn, de-thatch first.
  • Divide perennials  Perennials that are done blooming may be divided and/or moved.  The roots will have time to reestablish before frost.
  • Fertilize the lawn  Apply a winterizing fertilizer later in the month, a low nitrogen formula such as 18-0-12 ratio, to strengthen the lawn before winter without encouraging fast growth..
  • De-thatch  De-thatch the lawn every few years in September.  Aerate if you didn’t do it in spring.
  • 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.  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-b-gone in a tank sprayer is more effective.  It also allows you to spot spray individual weeds are target small areas.  Clover and creeping charlie require several applications.  With a pump sprayer you can target those every few to several days.  DO NOT spray new grass seedlings.
  • Remove dead plants  Shrubs, perennials or trees that have died should be removed.
  • Slugs are active  September brings slugs out in full force.  Apply diatomaceous earth or other slug controls.
  • Be prepared for frost  Be prepared to cover your tender plants and crops if frost is forecast.
  • Dig in compost  As you clean out the garden beds, dig in compost so the soil is ready in spring.
  • Plant peonies  Plant, or divide and transplant peonies between the end of August and October.  Remember that peonies prefer not to be disturbed, so divide only if the clump has gotten way too large.


  • Plant perennials  September is an excellent time to plant perennials.  Days are warm and nights are cool, perfect for establishing roots.
  • Plant fall bloomers  You can still pick up mums and asters in bloom for planting right now.
  • Plant bulbs  Plant spring blooming bulbs in September or early October.
  • Prune Oak and Walnut  By end of August through October it is safe to prune Oak and Walnut Trees.
  • Clean up fruit  Clean up and remove any fallen fruit.  Decaying fruit will harbor pests and disease.
  • Needle drop  Don’t be alarmed to see your evergreen drop some needles.  Old inner needles will drop as new needles form on the branch tips.
calendarSharon Dwyer