Gardening Tips for September 2025

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Annuals - Only buy summer annuals now if you need quick color until frost arrives. Now is the time to be planning for winter annuals (cool season hardy annuals that bloom all winter). Iceland Poppies and Pansies (buy and install in the last week of September through the first two weeks of October- protect from full sun on days above 90 degrees). For more about choosing and caring for Pansies watch The Gardening Tutor video Pansies 101: How to Choose, Plant and Care for Pansies.
Perennials - Sedum, Aster, Rudbeckia, Veronica, Fuchsias.
Frost Hardy Shrubs - Berberis, Hydrangea quercifolia, Pittosporum, Rosemary.
Veggies - Lettuce, Swiss Chard, Bok Choy.
Bulbs - Freesia, Alliums, Narcissus (daffodils), Ranunculus, Scilla peruvian.
Extras-Dormant Oil, Neem Oil, Frost Cloth, Stakes.

The Renaissance of the Garden in Fall

• Prune - Finish pruning many blooming plants, such as Veronica, Lobelia, Erigeron and others by the first week of September so they have time to bloom before frost. Watch The Gardening Tutor video on Shearing Plants to Encourage Flowers or Foliage. Prune roses to encourage more blooms before winter. Wisteria-thin out any crowded or overly long stems now to make it easier to cut back flowering stems in winter.
• Fertilizing - Apply one last dose of fertilizer for the season to shrubs so the new leaves have time to mature before frost begins at the end of October (here in Sonoma County CA). Container plants too will appreciate another round of fertilizing (Mary uses Maxsea). Watch The Gardening Tutor video: Two Quick Methods of Fertilizing. During winter, cool season annuals will still appreciate being fertilized monthly.
• Mulch - Apply a thick layer (at least 3 inches on top of soil) of compost as mulch in planting beds that will have winter annuals growing in them. Also, the veggie garden soil will appreciate some amending with compost and mulching on top with compost too. Veggies starts (small plants) such as Spinach and Lettuce love being planted directly into compost. The key is to keep the compost moist, this means more hand watering when the compost is new because when compost is new it is hydro-phobic (repels the water). Once the spinach and lettuce plants start growing well they can be on drip only (unless there is a heatwave when an extra shower will help them get through the last of summer’s heat).
• Bulbs: Spring flowering bulbs, such as Alliums, Freesia, and Scilla peruviana are in nurseries now. Choose bulbs that are blemish free and heavy for their size.  
• Pest Management – One last preventative spray of Neem Oil on Dahlias and Zinnias and other plants that tend to get powdery mildew will help prevent the mildew from starting. Scales insects are best removed by hand as sprays tend to only work to kill the crawlers (baby scale) when they are active, usually in spring. Use a plastic scraper or gloved hands to slide the scale off the stems of plants and let them drop into hot, soapy water. For Japanese Beetles Larvae in Lawns apply Milky Spore in fall. These and other grubs can also be managed by using Beneficial Nematodes (follow directions on the packet for best application times). Note: when a lawn has the larval stage of insects this can be a food source for raccoons or other critters, the goal is to remove the food source to try to keep raccoons from digging up a lawn and prevent lawns from having brown spots where grubs eat the roots of the grass.  

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ALL CONTENT and Photos by Mary Frost (no AI).