What to Do in the Garden in August (Cool-Climate US)

Start and sow

• Finish direct-seeding fall vegetables: the UMN window closes around mid-August for spinach and lettuce.
• Direct-seed carrots, beets, kohlrabi, kale, and snap beans early in the month; lettuce, spinach, radishes, and green onions can follow in late August (Purdue Extension).
• Order spring-flowering bulbs now for fall planting.
• Take cuttings of impatiens, coleus, geraniums, and wax begonias to overwinter indoors.

Lawn renovation window

• Seed new lawns or bare spots; early August to late September is the best seeding window for cool-season grass (UMN lawn care calendar).
• Early August through mid-October is the best lawn fertilizing window; mid-August through mid-October is best for aerating, and mid-August through September for dethatching (UMN Extension).
• Mid-August to late October is also a good window for laying sod.

Prune and maintain

• Don't fertilize woody plants now; it stimulates late growth that won't harden off before winter (Purdue Extension).
• Prune out and destroy raspberry and blackberry canes that bore fruit this year.
• Divide peonies from late August through September (UMN Extension).
• Keep newly established trees and shrubs watered, about 1 to 1.5 inches every 7 to 10 days in dry spells, and check young trees for girdling wires or twine.

Harvest

• Harvest onions after tops yellow and fall, then cure them in a warm, dry, well-ventilated spot.
• Harvest potatoes after the tops yellow and die.
• Pick beans, tomatoes, peppers, and squash often to keep plants producing.
• Harvest sweet corn when kernels are plump and ooze milky juice.

Sources

Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.

• University of Minnesota Extension — Upper Midwest home garden care schedule — Fall vegetable direct-seeding window runs through mid-August (spinach, lettuce); divide peonies late August-September
• University of Minnesota Extension — Lawn care calendar — Best windows: seeding early August-late September; fertilizing early August-mid October; aerating mid-August-mid October; dethatching mid-August-September; sodding mid-August-late October
• Purdue University Extension — August garden calendar (Indiana Yard and Garden) — Complete fall direct-seeding early August; plant greens late August; don't fertilize woody plants now; prune fruited bramble canes; onion/potato harvest cues; order spring bulbs; overwinter cuttings of annuals

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