August Gardening Tips, Tasks, and Problems


Trees & Shrubs

  • Roses should receive no further fertilization after mid-August, or 6-8 weeks before the average first frost date.

  • Bagworms have stopped feeding and are now attached to twigs or other structures. Insecticides are ineffective at this time of year. Manual removal or pruning is the most effective control.
  • Lightly prune hedges for the last time this season.

  • Panicle hydrangeas may flop over with the weight of flower heads. This is normal and removal is optional.

  • Second-generation of pine needles scale crawlers may be present on Mugo and Scotch pines.


Annuals & Perennials

  • Deadhead annuals and perennials as needed. Fertilize some annuals for the last time to encourage a new flush of blooms for the fall.

  • Iris borer moths emerge from the soil to lay eggs on iris leaves in late August.

  • Divide irises and daylilies as needed. When dividing irises, discard old centers and any borer-damaged parts.

  • Surprise lilies and water lilies are now blooming.



  • Zoysia lawns can receive their final fertilizer application in early August.

  • Check lawns for white grubs. If there are 10+ per square foot then apply an appropriate insecticide.

  • Lawns scheduled for renovation should have soil tested to determine nutrient levels.

  • Check lawn for sod webworm, larvae are feeding throughout the month.

  • Dormant cool-season lawns should be soaked now to encourage strong fall growth.


Fruits & Vegetables

  • Protect ripening fruits and vegetables from animals by covering them with netting, spraying repellent sprays, or using other tactics.

  • Sow seeds of beets, kohlrabi, lettuce, mustard, peas, radishes, spinach, and turnips now for the fall garden. Spinach may germinate better if seeds are refrigerated for one week before planting.

  • Thornless blackberries and fall-bearing red raspberries are ripening now.

  • Broccoli, cabbage, and cauliflower transplants should be set out now for the fall garden.

  • Apply treatment to peach and other stone fruit trees now to protect against peach tree borer.

  • Pinch the growing tips of gourds/squash once adequate fruit set is achieved. This directs energy into ripening fruits, rather than vine production.

  • High heat (90oF +) can cause pollination issues in cucurbits, tomatoes, peppers, and eggplants.

  • Squash vine borer damage may be prominent now; plants suddenly wilt and sawdust-like debris can be found near the base of the plant.

  • Look out for squash bugs. Destroy any egg masses, and use proper treatment for any adults/nymphs.



  • Be sure to give plants adequate water, especially during times of high heat. This will help defend the plants against drought and heat stress.

  • Hummingbirds are migrating now.

  • Monitor plants for spider mite activity. Hose off with a forceful spray of water.

  • Powdery mildew may be present on plants (specifically lilacs and peonies). No control is necessary and plants will recover. Keep an eye on plants in subsequent years and apply preventative fungicide in spring when leaves have begun to emerge.

  • Fall galls may be noticeable starting in late August.