Q. My backyard has a bermudagrass lawn and I would like to overseed with a winter ryegrass seed. When I have done this before, I “burned out” the bermuda by not watering it, then rented a power rake to de-thatch it. This year with all the rain, my bermuda is not turning brown. My concern is if the lawn is green the power rake will not remove the thatch. Also, which do you recommend annual or perennial rye seed and why? Dethatcher or verical mower. A. Overseeding bermudagrass with a cool season grass like one of the ryegrasses has a window of time which is optimum in the fall. This window is from September 15 to October 15. If you overseed to early, the bermudagrass is too active and will compete with your winter lawn. If you overseed too late, you run the risk that it will get too cold quickly and the overseeded grass may not all germinate and fill in your overseeded area.             The mantra for effective overseeding is having “good soil to seed contact”. In other words, the seed should rest on the soil when you overseed correctly. If the bermudagrass is too dense, much of the seed will not land on the soil and you will have a spotty winter lawn. Common Bermudagrass stolon             Sounds like you have the correct sequence for overseeding; time the overseed around October 1, September 15 turn off the water to the bermudagrass, September 21 mow as short as possible (rotary mower on the lowest setting is fine), power rake or dethatch until you see bare soil, apply seed, fertilizer, topdress the seed and fertilizer and water.             Bermudagrass lawns are usually mowed somewhere from ½ to 1 inch high. I like to let it grow to an 1½ in August/September. This produces more stem so I can “scalp” it better and get the seed to fall onto the soil for that good soil/seed contact.             You can use annual ryegrass if you want but it is coarse textured, light green and rough to the touch. Perennial ryegrass is a much prettier grass and soft to the touch. You can put all the nitrogen you want on annual ryegrass and it will just not get the same dark green color as perennial ryegrass. It is more expensive but will give you a much prettier lawn.