University of Maryland Extension

September Tips & Tasks

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lilac leaves infected with powdery mildew
Powdery mildew on lilac

Outdoor Yard and Garden Tips

  • Powdery mildew may be seen now on many trees, shrubs, and perennials, like pin oak, roses, lilac, phlox, peonies, and monarda. This fungal disease favors high humidity but unlike other fungi does not require wet weather to thrive. It usually appears on plant foliage as a grayish, powdery coating on upper leaf surfaces. When possible select resistant cultivars. No chemical control is necessary.

  • Poison ivy leaves will begin to turn red this month. Don’t be fooled by their fall color change, the leaves are still very irritating. Do not handle or shred the leaves and do not burn the vines. 

  • Avoid planting one type of tree or shrub (a monoculture) when planting a living screen. Diseases and insects are typically host specific so you run the risk of loosing the entire screen if a pest or disease attacks your plants. Select several different types of trees and shrubs, both evergreen and deciduous, to prevent this from occurring.

  • In most cases healthy, mature trees and shrubs do not require fertilizers. Woody plants receive nutrients from lawn fertilization if their roots are adjacent to or growing under the turf area.  Their roots also take in nutrients from decaying mulches and leaves and from the minerals in soil.  

  • Hold off pruning trees and shrubs until later in the fall into the winter. Pruning stimulates growth and any new growth produced now will not have a chance to harden off before winter. 

  • Spruce spider mites are active again on evergreen trees. Monitor for this pest by tapping branches while holding a piece of white paper underneath. Look for moving specks. They can be controlled with ultra-fine horticultural oil (do not use on blue spruce). Follow label instructions.
  • Plant garlic now through mid-November for a July 4 harvest next year. Plant the cloves root end down; space them 4-6 inches apart and cover with 1-2 inches of soil. Mulch the garlic bed with fallen tree leaves.  

  • Full size green tomatoes can be brought indoors to ripen. They ripen more quickly if placed in a paper bag with a banana or apple. The ethylene gas released from the fruit will help to ripen the tomatoes.

  • Harvest pumpkins and winter squashes when the rind hardens (fruits can tolerate a light frost).  Cut them from the vine leaving a 4-5 inch handle, handle gently, and store in a cool, dry location until ready to use.   


    oat and rye seed cover crop seeds
    Cover crop seeds ready for planting

  • Time to plant cover crops to protect and improve the soil in your vegetable beds. 

  • Harvest figs when they soften slightly. Ants may enter the small eye at the bottom of the fruit as the fig ripens.

  • Prune out the dead raspberry and blackberry canes that fruited this past summer. Fall fruiting raspberries and blackberries can be mowed to the ground in late winter.
  • Apply lawn fertilizer in the fall and fertilize according to the UME fertilizer schedule.  Make sure to sweep any fertilizer that lands on sidewalks or driveways back onto grassy areas.

  • Have a difficult area in your yard to grow a lawn? Refer to The Challenge of Growing a Lawn in Maryland and Lawn Alternatives

  • Leave the large seedheads of black-eyed Susans, coneflowers, and other perennials for birds to feed on over the winter.

  • House mice and sometimes field mice may be more noticeable around and in homes due to the onset of cool weather. Keep grass and weeds properly mowed around your house and seal all cracks.

  • Avoid storing pesticides over the winter in sheds and garages. Cold temperatures can cause these materials to become ineffective. If you have questions about the efficacy of your pesticides call the manufacturer, using the phone number listed on the label. For additional pesticide storage information visit the National Pesticide Information Center website

Indoor Plant and Insect Tips

red-leafed begonia houseplant
Begonia

  • Before moving houseplants back indoors check plants for antsearwigspillbugs, and other nuisance insects.  Wash off insect pests or apply a labeled houseplant insecticide to control any plant pests such as aphids, scales, spider mites and mealybugs.
  • Avoid wetting the leaves of fuzzy leaved plants like African violets. Wet foliage can cause leaf spotting.
  • Be careful not to over water houseplants during the indoor adjustment period which can take several weeks.

  • As houseplants that were outdoors for the summer adjust to less light indoors leaf yellowing and drop is possible. 

  • It's early fall - prepare for the invasion of insects! Crickets, multicolored Asian lady beetlesboxelder bugsstink bugs, cluster flies, and other innocuous insects will attempt to enter your home this fall to overwinter. Caulk, weatherstrip and seal up all cracks, and entry points around your house foundation, vent openings, windows, and doorways to prevent these critters from coming indoors.
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