Gardening by Month - September
Monthly Tips and Tasks

Category
Week
Activity
  1 2 3 4  
 Ornamentals x x x x Continue planting evergreens now.
  x x x   Cuttings of annuals can be taken now to provide vigorous plants for overwintering.
  x x x   Herbs such as parsley, rosemary, chives, thyme and marjoram can be dug from the garden and placed in pots now for growing indoors this winter.
    x x x Except tulips, spring bulbs may be planted as soon as they are available. Tulips should be kept in a cool, dark place and planted in late October.
    x x   Begin readying houseplants for winter indoors. Prune back rampant growth and protruding roots. Check for pests and treat if necessary. Houseplants should be brought indoors at least one month before the heat is normally turned on.
      x x Perennials, especially spring bloomers, can be divided now. Enrich the soil with peat moss or compost before replanting.
      x x Divide peonies now. Replant in a sunny site and avoid planting deeply.
      x x Lift gladioli when their leaves yellow. Cure in an airy place until dry before husking.
      x   Poinsettias can be forced into bloom for Christmas if they are moved indoors now to a sunny windowsill. Each night, they must be kept in a cool, dark place where there is no light for 14 hours. This must continue until proper color is achieved in 6-10 weeks.
 Lawns x x x x Cool-season lawns are best fertilized in fall. Make up to 3 applications between now and December. Do not exceed rates recommended by fertilizer manufacturer.
  x x x x If soils become dry, established lawns should be watered thoroughly to a depth of 4-6 inches.
  x x x x Begin fall seeding or sodding of cool-season grasses. Seedbeds should be raked, dethatched or core-aerified, fertilized and seeded. Keep newly planted lawn areas moist, but not wet.
    x x x Lawns may be topdressed with compost or milorganite now. This is best done after aerifying.
      x x It is not uncommon to see puffballs in lawn areas at this time.
      x x Newly seeded lawns should not be cut until they are at least 2 or 3 inches tall.
 Vegetables     x x     Egyptian (top-setting) onions can be divided and replanted now.
  x x     Sowing seeds of radish, lettuce, spinach and other greens in a cold frame will prolong fall harvests.
    x x x Keep broccoli picked regularly to encourage additional production of side shoots.
    x x   Pinch out the top of Brussels sprout plants to plump out the developing sprouts.
    x x   Harvest herbs now to freeze or dry for winter use.
    x x   Tie leaves around cauliflower heads when they are about the size of a golf ball.
      x x Pinch off any young tomatoes that are too small to ripen. This will channel energy into ripening the remaining full-size fruits.
        x Sow spinach now to overwinter under mulch for spring harvest.
 Fruits     x       Pick pears before they are fully mature. Store in a cool, dark basement to ripen.
      x x Bury or discard any spoiled fallen fruits.
        x Paw paws ripen in the woods now.
        x Check all along peach tree trunks to just below soil line for gummy masses caused by borers. Probe holes with thin wire to puncture borers.
 Miscellaneous     x x x x Autumn is a good time to add manure, compost or leaf mold to garden soils for increasing organic matter content.
  x x     Monitor plants for spider mite activity. Reduce their numbers by hosing off with a forceful spray of water.
    x x x Seasonal loss of inner needles on conifers is normal at this time. It may be especially noticeable on pines.
September Pests and Problems


Now is the time to reseed dead areas in your cool-season lawn, such as fescue and bluegrass. These areas should be reseeded between September 1 and mid-October. If this also involves killing any existing grass, kill these areas with an herbicide at least 2 weeks before planting seed. Stop fertilizing, dethatching, and core aerifying of warm-season grasses now. Resume again after green-up in late spring next year.
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Perennial Grassy Weeds in Lawns and Gardens
Orchard grass Dactylis glomerata in fescue lawn (Festuca
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Perennial Broadleaf Weeds in Lawns
Dandelion in bloom, a common perennial weed in lawns and gardens 
 

Monitor and treat for grubs in lawns if required. Treating is only necessary if 10 or more grubs are found in a one square foot area when grass is actively growing. If this threshold is met, treat with fast acting trichlorfon (Dylox) now. Treatment with imidacloprid (Merit) or halofenozide (Mach 2) should have been made in July as they take longer to act.
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Grubs in Lawns
Feeding by grubs (Coleoptera) causes dead spots in lawn in late summer. 
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Grubs in Lawns
Grubs (Coleoptera) can be found when the grass killed by their feeding is pulled back. 
 

Scorch is a common problem in hot, dry weather. Be sure and keep plants well watered during periods of drought. Stressed plants are more susceptible to attack by insects and disease. Many plants may also exhibit wilting leaves or yellowing foliage due to lack of adequate water. Water during dry spells.
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Scorch, Sunburn, and Heat Stress
Scorch on dogwood (Cornus) leaves 
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Environmental
Drought stress on magnolia (Magnolia
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Drought and Water Stress
Close-up of drought stress on magnolia (Magnolia

Galls are common on many plants throughout the season. Generally galls on leaves are just cosmetic and do little damage. Horned and gouty oak gall affects twigs and, although usually not a serious threat to the health of the tree, can be unsightly. Unfortunately, little can be done to control them. An arborist can remove them, but there is no guarantee that they will not recur. In mid- to late summer fall webworms may also be seen.
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Galls on Trees
This gall on an oak leaf (Quercus) looks like an oak flake gall caused by a wasp (Hymenoptera) but dissecting the gall is the only sure way to tell what caused the gall 
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Gouty, Horned and other Twig Galls
Gouty oak gall on pin oak (Quercus palustris) caused by a wasp (Hymenoptera) 
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Fall Webworm
Fall webworm (Lepidoptera) on crabapple (Malus

To force poinsettias into bloom for Christmas they should be moved indoors by the 3rd week in September to a sunny windowsill. Each night, they must be kept in a cool, dark place where there is no light for 14 hours. Continue until proper color is achieved. This may take 6-10 weeks or longer. Water and fertilize on a regular schedule.
 
 
 

Check your lawn for sod webworms now.
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Sod Webworm
Sod webworm adult (Lepidoptera) on lawn grass 
 
 

Mushrooms and puffballs are commonly found in lawns at this time of year. Most are the fruiting bodies of useful fungi that decompose organic matter in the soil or exist in a beneficial relationship with the living roots of nearby trees. They cause minimal harm to grass. No chemicals are currently registered for control. Physically remove them and treat as yard waste.
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Fairy Rings
Fairy ring in lawn 
 
 

White pines normally shed old needles in the fall, usually beginning mid to late September. The yellowing and dropping of these interior needles is normal and should not cause concern.
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Normal
Yellowed interior needles on white pine (Pinus strobus) caused by normal needle drop; note that growing tips are unaffected 
 
 

Powdery mildew may appear as a white coating on the leaves of lilacs, dogwoods, and other plants as temperatures cool in autumn. Damage to leaves this late in the season is purely aesthetic and is not harmful. No treatment is required.
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Powdery Mildew - Outdoors
Powdery mildew on lilac (Syringa
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Powdery Mildew - Outdoors
Powdery mildew on underside of oak leaves (Quercus
 

Moles may cause damage to lawns as they feed on earthworms, grubs and other soil inhabitants. Control options are discussed in our IPM sheet on moles below.
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Moles
Mole tunnels in lawn 
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Moles
Mole, common lawn pest 
 

Keep your eyes open for magnolia scale. Unlike most other species of scale, crawlers of the magnolia scale are present and active now. This is the ideal time for controlling the most vulnerable stage of this troublesome pest.
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Magnolia and Tuliptree Scale
Magnolia scale (Hemiptera) on magnolia (Magnolia) with sooty mold growing on the honeydew that has dropped on the leaves 
 
 

Unlike many spider mites that are most active in hot, dry weather the spruce spider mite proliferates in the cool temperatures of spring and fall. They can cause substantial damage to spruce, hemlocks, and junipers. Examine yellowing needles on spruce now for these mites. Treat if necessary. Controls are the same as for other spider mites. Also check of whitefly, which can become numerous at this time of year.
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Spruce spider mite
Spruce spider mite damage (Acari) on spruce (Picea
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Whitefly - Outdoors
Close-up of whitefly (Hemiptera) adult and pupae on sweet potato vine (Ipomoea batatas
 

Rose rosette can appear at any time of year but frequently shows up on new fall growth. If witches’-brooms are found on rose bushes at this time of year, suspect rose rosette.
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Rose Rosette
Rose rosette on rose (Rosa
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Rose Rosette
Rose rosette on rose (Rosa
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Rose Rosette
Symptomatic thorns on rose (Rosa) caused by rose rosette 

Purplish-brown needles on blue and other spruces at this time of year is often caused by Rhizosphaera needlecast disease. Infection occurs in May and June long before symptoms appear. Fungicides are available for control but must be applied in spring before infection occurs.
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Rhizosphaera Needlecast
Purplish cast of needles on Colorado blue spruce (Picea pungens) caused by rhizosphaera needlecast 
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Rhizosphaera Needlecast
Needles of Colorado blue spruce (Picea pungens) dropping due to rhizosphaera needlecast disease 
 

Both box elder and red-shouldered bugs are commonly seen in large masses on tree trunks and the siding of buildings at this time of year. They do little damage to trees but will feed on the seeds. Homeowners may find them objectionable especially when they migrate indoors. (They look very similar to the milkweed bugs below.)
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Milkweed Bugs
Milkweed bug nymphs (Hemiptera) in various stages 
 
 

Asian multicolored lady beetles may also be found at this time of year. For home gardeners they are beneficial but a nuisance. Control out of doors is not recommended, but insects found indoors can be vacuumed and disposed of.
 
 
 

Be alert to the flight of peachtree borer adults that are active from July - September. See August and May for control measures. August and September are the best times to implement controls for carpenter bees.
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Peachtree Borer
The thick, gummy or jellylike sap mixed with frass at the base or crown of this peach tree (Prunus) is caused by a heavy infestion of peachtree borers (Lepidoptera) 
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Carpenter Bees
Close-up of the exposed tunnels made by carpenter bees (Hymenoptera) for their eggs. The grooves in the wood were made by woodpeckers drilling for the larvae.