The Ornamental Garden in September

  • By Pat Chadwick
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  • September 2015 - Vol.1 No. 9
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It’s September – a magical time of year when the late afternoon sun casts a golden glow over the entire landscape. The air, though still warm, feels cooler following the dog days of summer and the days are growing noticeably shorter. As temperatures begin to cool down, it’s time to swing into action to prepare the ornamental garden for the transition into autumn.

Many annuals, such as petunias, marigolds and zinnias, start to look leggy, floppy, or just plain tired by September. Begin your fall garden cleanup by removing spent annuals and composting them unless, of course, they are diseased, in which case, they should go straight into the trash.

Other annuals, such as begonias, coleus, geraniums and lantana, should still be going strong. To keep the floral show going for as long as possible, protect tender plants such as these when night-time temperatures turn chilly.

If you’re thinking about digging up some of your annuals and bringing them indoors for the winter, don’t do it! They’re not likely to survive the transition indoors. You’ll have far better success if you take stem cuttings and root them in pots. Give them a sunny spot on a window sill or other suitable well-lit place so that you can enjoy them indoors this winter. Then, next spring, you will be able to return the plants to the garden.

Do you love early-blooming annuals, such as larkspur, love-in-a-mist (Nigella), snapdragons, and calendula? These plants like cool growing conditions. Try direct sowing the seeds in the fall rather than next spring.

Begin to prepare your houseplants for the return indoors. Day-time temperatures may still feel hot to you, especially during the first half of the month, but nights will be noticeably cooler. When night-time temperatures begin to fall into the 50s, move house plants indoors. To prepare for the transition, move your house plants to a shady spot about 2 weeks in advance so that they get used to lower light levels. Remember – you gradually acclimated your plants for their transition to the sunny outdoors this spring. Now you need to reverse the process.

Before you bring those potted plants indoors, thoroughly inspect them for insects. Scale, white fly, mealy bugs and fungus gnats are just some of the beasties that may catch a ride indoors on your plants.

One last thought on house plants. Thoroughly wipe down all potted plant containers to remove dirt, debris, spider webs, and insect eggs or larvae. Inspect the bottoms of containers as well as the bottoms of saucers for insects that may be hiding there. Those are ideal places for spiders to hide as well as stash their egg cases.

Early fall is an ideal time to divide and transplant spring-flowering plants. Many perennials, such as daylilies, garden phlox, irises, and oriental poppies, should be divided every three to four years.   Pick a cool day for this task. As you divide plants and transplant them, water them well and continue to keep them watered so that they become well established in the garden before the onset of winter.

September or early October is the ideal time to divide or move peonies so that they become well established before winter. Peony tubers are very fragile, so be particularly careful to keep the root mass as intact as possible.   Space the plants at least three feet apart. This is important: Plant the roots so that the buds are only about one to two inches below the soil surface. If you plant them deeper, they will not bloom.

Fall is traditionally the best time of year to plant new trees and shrubs in the landscape. To give those woody ornamentals the best possible chance for success, keep them well watered throughout the fall. Inadequate moisture can stress the plant making it more susceptible to winter damage. Don’t rely on rainfall alone to maintain adequate moisture levels. To help hold in moisture as well as moderate the soil temperature,  spread a three-inch layer of mulch over the rootball area after it has been well watered.  Be careful not to pile mulch against the plant’s stem or trunk.

As you plan ahead for next year’s spring garden, expand your horizons and experiment with bulbs other than daffodils and tulips. Invest in early-blooming bulbs such as snowdrops, crocus, scilla, dwarf early-blooming iris, winter aconite, narcissus, glory-of-the-snow, and other easy-to-naturalize hardy bulbs for planting this fall. A naturalized display of blue grape hyacinths (Muscari), for example, can be stunning in the early spring. As extra incentive for you to plant these early bloomers, deer, voles, and other pesky critters generally do not bother them.

Note for next season’s garden: If you’re not already doing this, try incorporating more native plants into your late summer/early fall garden. Try Joe Pye Weed, goldenrod (Solidago), asters, ironweed, and boltonia in sunny, well drained sites.   All of these plants are butterfly magnets. For the shade garden, try turtlehead (Chelone), woodland aster (Aster divaricatus), or cardinal flower (Lobelia cardinalis).


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