Still have some empty spaces in your garden beds? September’s cooler temperatures and rainfall make it a great month for planting, and new plants still have sufficient time for root development before the ground freezes. Trees and shrubs should be planted by the end of September, and perennials by mid-October.
Tropical and succulent plants, as well as herbs like bay and rosemary, can be overwintered as houseplants in a sunny location. Gradually move these plants into increasing shade outside before moving them inside to accustom them to the lower light levels.
Divide spring-blooming perennials such as iris (Iris spp. and cvs., Zones 3–9) and peonies (Paeonia spp. and cvs., Zones 3–8). Water plants thoroughly the day before you divide them, and after replanting, water and mulch around your new divisions to maintain adequate soil moisture and prevent heaving in winter.
Refresh containers by removing faded plants and popping in colorful, cold-tolerant fall plants such as pansies (Viola × wittrockiana, annual), mums (Chrysanthemum spp. and cvs., Zones 5–9), asters (Aster spp. and cvs., Symphyotrichum spp. and cvs., and Eurybia spp. and cvs., Zones 4–8), kale, and grasses.
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