Lawn overseeding for fall and winter.
In Portland area what type of grass seed would you recommend for cooler weather.
Multnomah County Oregon lawns and turf
In general, in Oregon, we plant cool-season grasses which include perennial ryegrass, the 3 fine fescues, tall fescue, Kentucky bluegrass (not recommended in western Oregon), and colonial or highland bentgrass. There are pros and cons to each variety and lawns generally convert over time to either annual bluegrass or bentgrass from seed already in the soil seed bank. If you are planting this late, perennial ryegrass should be in the mix - at least as a nurse grass - because it germinates quickly and will give your lawn cover while the other grasses (e.g. fine fescue or colonial bentgrass) are growing in. Tall fescue is fairly fast to germinate now but not as fast as perennial ryegrass.
If you want the nicest lawn initially, plant 100% perennial ryegrass at 10 lbs of seed per 1,000 sq. ft. Many people now are planting tall fescue because they want to water less, or not at all, and tall fescue will stay green longer with less water. However, tall fescue is coarser textured than perennial ryegrass so it doesn't look at nice. If you are not going to water in the summer, do not plant perennial ryegrass - the best choice is colonial or highland bentgrass, but as mentioned above, plant perennial ryegrass with it at about 4 lbs of seed per 1,000 sq ft (the seeding rate for bentgrass is 1 or 2 lbs per 1,000 sq ft). Both these grasses are susceptible to winter diseases and you need to fertilize a couple times in the fall to minimize the damage.
Fine fescue (creeping red) is an option that can tolerate long term drought if you plan not to water in the summer, but it takes regular watering in the summer to look good. If not, it has a summer dormancy and will turn brownish in color. It is has the finest texture. Fine fescue does not handle heavy traffic well (nor do the bentgrasses).
If you plant bentgrass, you should mow it lower rather than higher. 3/4" - 1" with a push reel mower would be great. If all you have is a rotary, in general, the lowest setting is most likely the best setting for most rotary mowers but use your judgement if your lawn is not smooth enough and you are getting bad scalping.
Fine fescue and bentgrass only need 1 or 2 fertilizer applications per year whereas perennial ryegrass needs at least 4 to look its best, and maybe 6 in the first year depending on whether you return clippings (you should) and the nutrient status of your soil. Tall fescue less than perennial ryegrass and more than fine fescue and bentgrass.
I hope this helps.