August Gardening Tips
for the Willamette Valley

by Rod Smith

Former Iowa Certified Nurseryman and
Oregon Certified Nursery Professional

@copy 2002-2023 Rodney A. Smith
All rights reserved.


Perennials can be started from seed, but sow deeper than normal.

Radishes and carrots can still be planted for a fall crop.


Continue to feed lawns every six weeks.

Give roses and blooming plants one last feeding so they will harden off before winter.


Continue deep watering. Lawns need an inch of water each week when temperatures are near 70 degrees, more during hot weather. Plants will need extra water during hottest weather. Rhodies and Hydrangeas growing in the sun can be cooled down by sprinkling them in the afternoon.


Cut off old flowers to encourage repeat blooming.

Pruning overgrown deciduous trees and shrubs in the summer will slow down their growth the following year and reduce overcrowding.

Early August is the last chance to prune hedges and still have some new growth to hide the brown edges where leaves have been cut.


Continue to spray for leaf spot diseases and powdery mildew if plants are watered by overhead sprinklers.

Spray rhododendrons twice a month through August for root weevils if the leaves have notches on the edges.

Check rhododendrons and azaleas for tiny, light brown spots on the underside of the leaves caused by lace bugs. Severely damaged leaves are almost white. Spray with a product containing Imidacloprid, such as, Bayer Advanced Garden Tree and Shrub Insect Control, or Spinosad, such as Captain Jack's Dead Bug Brew, to prevent lace bug damage. Both are toxic to bees, so do not use on plants with open flowers.

Spider mites are a serious problem on arborvitae and needle leaf evergreens during hot weather. Spraying once a month makes them worse. Apply two miticide sprays a week apart, or according to directions on the package. Hosing down the plants once a week with plain water also helps.

Use a lawn week killer for broadleaf weeds.

Check lawns for dead spots caused by common cranefly and billbugs.
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