Reseeding a lawn
Hi, My lawn is overrun with weeds. Probably less than half is actually grass. I am planning to tear it up and reseed. I understand that I probably need to apply a weed killer as the lawn is establishing itself. Since I'm going to do that, will it work to just till up the lawn, leaving the old grass and weeds, amend the soil, and then reseed? Or do I need to get rid of the old grass and weeds? Is it too late to do it now? Thanks
Washington County Oregon
Hello and thank you for asking about your lawn. The recommendation is that you plant a lawn or do major renovations in early fall (mid-August to mid-September). Early May to mid-June is the usual spring window which isn't ideal, but works many years.
The publication "Practical Lawn Establishment and Renovation", EC 1550 from Oregon State University Extension: http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/19278/ec1550.pdf is excellent. It is 26 pages of useful information tailored for our area. The last page is a step-by-step guide to establishing a lawn from seed, but the details throughout the publication are helpful.
OSU has other publications about lawn, use this "Publictions and Multimedia Catalog" page search box: http://extension.oregonstate.edu/catalog/.
Your question about getting rid of the current weeds is a good one. Since you should wait for May to seed, I think killing perennial weeds first, like dandelions, could be worthwhile. It might depend on the spring weather, as weeds generally need to be growing if you are treating with herbicide. Follow directions for herbicide carefully, watching the timing, temperatures, and each other detail.
This gardening-tip article, "Pick a low-maintenance grass...", from OSU Extension, is a good overview: http://extension.oregonstate.edu/gardening/pick-low-maintenance-grass-lawn-september It indicates October is okay to seed a lawn, but this year the heavy rains have started so early, it would be more of a gamble for you than those years with warm dry weather through the month.
Best wishes, hope this information helps.
Thanks so much for the quick reply. I will read the references you gave.
I realized that early October is late for reseeding and it does seem like the fall is early, but shouldn't the rain actually help establish the lawn? Isn't the problem with seeding late the cold rather than the wet?
Hello again. Planting now is a gamble. Heavy rains such as we've had the last couple of weeks will often wash seeds away or cause erosion if you had worked the soil. Will there be more rain like that before seeds sprout?
Then there is the temperature, as you state. Ideal is about 65. (A prior Ask an Expert response https://ask.extension.org/questions/114286) The National Weather Service prediction right now in my area of Washington County is night temperatures of 39-41F degrees. Will the soil get too cold for the grass to sprout and grow well? Hard to say, actually. One way to look at it is that grass seed isn't expensive, and if it doesn't grow, you can reseed in spring. If you do that, I'd say that leaving the current grass to help hold the soil for the winter is best. I'm not sure you can till the soil anyhow when it is this wet.
Sorry I don't sound more definite. There are many variables. The sun and the slope of your location all might make a difference with your success too. Take a look at the renovation parts of the lawn publication EC 1550, as leaving the old lawn is more renovation that establishing.