As a newcomer to Oregon, I am uncertain when to fertilize my lawn. It is getting yellow patches. The soil is clay and very mucky wet. What type of fertilizer is best, and when should it be done?
Multnomah County Oregon lawns
Thank you for your question about your lawn. The first thing you need to address is why your soil is holding water so much. Although we have had rain recently, it should have drained. All of our soils here are clay, and getting it 'lightened up' is a priority. Assuming that you don't want to put in a drain system, you can improve the soil by adding organic matter to it, as this Extension article explains. How to do it is explained here, starting on page 9, with specific information for lawns on page 10. Pooling water doesn't allow roots to have the air in the soil necessary to grow, and they will die--true of almost every plant! Just wait until the water has drained before you start walking on it. You can spread organic matter on top.
The second question you ask is about fertilizer. Until you get the soil issue resolved, reseeding and fertilizing will just be a waste of both. So, once you've added organic material, you can start thinking about renovating (reseeding) and fertilizing your yard. I appreciate that this article is a long one, but the seeding information starts on page 10, and the fertilization on page 12. You essentially do both simultaneously, since that's when the grass seeds will begin to need nourishment. Just don't overlook the paragraphs on mulching after reseeding, starting on page 13, and irrigation, page 14.
I appreciate that this is a lot to absorb, but you have to catch up! Good luck!