Rose City Roots

Gardening in Portland since 1996.

Portland lawn overseeding August with rake, grass seed, and empty vegetable bed ready for cover crop

Overseeding Lawns and Fall Cover Crops

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Monday's 94°F and Tuesday's low 90s mean the heavy prep waits for Wednesday, when highs drop into the low 80s and stay there. Saturday's rain will complete the job.

This Week's Action List

  1. 1

    Hold the lawn work Monday and Tuesday while highs sit around 90°F. Deep soak established turf with 1 inch of water at dawn Monday, measured with a tuna can under the sprinkler, and skip fertilizer until temperatures drop.

  2. 2

    Starting Wednesday, when the forecast eases to 85°F, dethatch thin or compacted lawn areas with a stiff rake or rented power rake, then overseed with a PNW perennial ryegrass and fine fescue blend at 6 to 8 pounds per 1,000 square feet.

    Starting Wednesday, when the forecast eases to 85°F, dethatch thin or compacted lawn areas with a stiff rake or rented power rake, then overseed with a PNW perennial ryegrass and fine fescue blend at 6 to 8 pounds per 1,000 square feet.
  3. 3

    Keep newly seeded lawn damp with 5-10 minute watering twice a day for 10 to 14 days. Ryegrass germinates in 5 to 7 days at current soil temps near 70°F, and fescue follows around day 10.

  4. 4

    For empty vegetable beds coming out of production, sow crimson clover at 1/2 pound per 100 square feet or winter rye at 2 pounds per 100 square feet. Both go in from now through mid September and will hold soil through winter rains.

    For empty vegetable beds coming out of production, sow crimson clover at 1/2 pound per 100 square feet or winter rye at 2 pounds per 100 square feet. Both go in from now through mid September and will hold soil through winter rains.
  5. 5

    A common mistake in August is fertilizing woody shrubs and trees to push a last flush of growth. Stop nitrogen feeding on shrubs, trees, and roses now so new wood hardens before the first mid November frost.

  6. 6

    Watch tomato plants closely after Thursday's slight bump in humidity and the rain in the forecast. Cool foggy mornings plus warm afternoons are peak late blight conditions, so pull any leaves with dark greasy lesions and bag them in the trash, not the compost.

  7. 7

    Slugs return fast once nights sit in the upper 50s and low 60s, next week's low temperature range. Scatter iron phosphate bait around brassica transplants and newly sown lettuce and spinach beds before Saturday.

    Slugs return fast once nights sit in the upper 50s and low 60s, next week's low temperature range. Scatter iron phosphate bait around brassica transplants and newly sown lettuce and spinach beds before Saturday.
  8. 8

    Clean gutters and check rain barrel overflow diverters this week while the roof is dry; September rains are not far.

Frequently Asked Questions

When is the best time to overseed a lawn in Portland?

Late August through mid September is the ideal window in Zone 8b. Soil temperatures sit in the 65 to 72°F range that ryegrass and fescue germinate fastest in, and the coming fall rains reduce watering demand once seedlings establish. Aim to have seed down at least two weeks before the first sustained rains.

What cover crop should I plant in Portland vegetable beds in August?

Crimson clover is the go to for beds that will be replanted next spring, since it fixes nitrogen and winter kills or turns in easily. Winter rye is better for beds you want strong erosion control on through heavy winter rain. Sow either from late August through mid September at Zone 8b timing.

Can I still fertilize my lawn in late August in Portland?

A light fall fertilizer application at overseeding time is fine, but hold off on any high nitrogen feed until temperatures moderate below the mid 80s later this week. On woody plants, stop nitrogen feeding entirely now so new growth hardens before frost.