Gardening Tips for September 2025

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• Cool-Season Annuals - The last week of September through the first two weeks in October is the optimal time to plant winter flowering annuals, such as Pansies, Iceland Poppies, and Calendula. There are other annuals that can be planted later in the year. New plantings may need protection during heatwaves. For best bloom, plan ahead so cool-season annuals are planted where they get good winter sun.
• Perennials - Frost hardy perennials, such as Lavender, Achillea (Yarrow), Columbine, Rudbeckia, Geum. Subscribe to The Gardening Tutor Newsletter to see which other perennials to buy now, it might surprise you.
• Trees - Bloom color can be mistakenly mislabeled. If you're looking for a specific color of Lagerstroemia indica (Crape Myrtle) buy now before blooms fade until next year. Start shopping later this month for trees, such as Chinese pistache, that have beautiful fall color to their leaves.
• Winter Vegetables -  Spinach, Lettuce, Swiss Chard, Broccoli, Peas, Beets, and Carrots.  In Sonoma County, September is the optimal time to get many of your veggie starts and seeds in the ground while the soil is still warm from summer. Labor Day is a good soft target reminder of when to get veggie plants and seeds planted.  New plants may need protection during heatwaves.
• Bulbs - Spring flowering bulbs will be arriving in local nurseries this month, shop early for best selection. Choose bulbs that are heavy for their size and free of blemishes. Here are just a few of the choices for spring bloom: Alliums, Anemone, Crocus, Daffodils, Freesia, and Sparaxis.
• Extras - Frost Cloth (also used as row cover to protect new veggies from insects), Dormant sprays.

• Pruning - Alstroemeria - once a stem has finished flowering, pull the stem completely out by using a quick tug. If you feel that if you tug roots want to come out then put your fingers on each side of the stem at ground level and then pull it out. This will tell your Alstroemeria to make new stems. No new growth happens on the stem once you cut for flower harvest or the flowers are finished. Continue to prune off spent Fuchsia flowers. Shape Phlomis fruticosa (Jerusalem Sage) by cutting back to healthy side shoots. Clean up unwanted growth on frost hardy vines. Erigeron, Teucrium chamaedrys, Alyssum, Oregano can still be sheared if you missed doing this task in August. Watch The Gardening Tutor Video: Shearing Plants to Encourage Flowers or Foliage. Frost season in Sonoma County begins at the end of October so shear plants in time for them to fill in and bloom again before frost. Contact Mary for an Appointment to Learn What to Prune Now.
• Pest Management - Notice which frost-hardy plants have powdery mildew and plan to spray when dormant. You can spray them now but depending on the plant the fungicide may just roll off the mildew and not get rid of the problem. Continue to bait for snails, slugs, earwigs and sowbugs (especially where you plan to plant new bloomers or veggies). When digging in the soil you may find immature pests that look like caterpillars (cutworms) or little, hard brown cocoon-like (pupa), discard these in hot, soapy water.
• Fertilizing- Summer annuals can continue to be fertilized once or twice a month until frost kills the plant. Mary uses Maxsea fertilizers.  
• Mulch - Fall is a great time to apply mulch to the garden. Watch The Gardening Tutor's Video: Mulch vs. Compost.
• Weeding - Bermuda Grass is hitting its peak now before it starts to go dormant in winter. What an insidious weed! Herbicides only brown the top grass blades and do not kill the whole plant. The roots can go down several feet in the soil. Bermuda Grass spreads by seed, by underground rhizomes (underground roots) and stolens (above ground roots)! Pulling it out by as many roots as you can is really the best management. Sheet mulching can work somewhat too.   

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ALL CONTENT by Mary Frost (no AI).