Our lawn is 2 years old. It was done by the builder after moving in.

This spring the grass is very yellow. I did some research and decided to aerate and fertilize the lawn.

On Saturday I had the lawn aerated, then I did a soil test which showed the soil was extremely low on nitrogen and potassium, but the phosphorus levels were okay. I used fertilizer 30-0-9 the same day (Saturday).

I'm wondering now if I should overseed the grass as well. Is it too late now that I've already fertilized? Is there even a point to overseeding right now or should I wait until the fall?

Any suggestions or advice would be greatly appreciated.

Also, after aerating, the cores should on average about 0.5 to 1 inch of thatch build up.

Where are you? Naming the town and state usually works. Giving the USDA hardiness zone never works.
What kind of grass do you have?
How frequently are you watering and for how long?
How high/low are you mowing?
How often do you fertilize and with what? If this is the first time you fertilized, then that question is answered.

There is seldom a point to seeding in the spring. Grass sprouting now usually dies by July from the heat stress. Seeding in the fall gives the roots much more time to penetrate into cooler parts of the soil. Also seeding now activates all the crabgrass seed along with any new grass seed. You don't need that.

Thatch after 2 years? And without fertilizer? We really need to know your watering schedule.

I live in Canada, Ontario to be exact. I have no idea what kind of grass I have.

We just came off the winter, so I haven't watered since last summer. When I did water, it was maybe 1 or 2 times a week at best? Maybe for an hour each time.

I was mowing pretty low, probably removing 1/2 of the grass blade each time.

Since getting the lawn, I've maybe fertilized 4 times. Everytime with the seasonal version of Scotts from the hardware store.

At least your answers tell me what you don't have, so while I still might embarrass myself, it won't be as bad as it might have been.

Based on location and the fact that ryegrass and bentgrass are rare, you likely have a fescue lawn possibly with some Kentucky bluegrass. Fescue is a bunch type grass that grows in clumps. To have a nice fescue lawn, you have to have a lot of clumps close together. Kentucky bluegrass is a sod forming type grass that will spread over the top of the surface and fill in the spaces left by sparse clumps of fescue. Fescue likes to be mowed at your mower's highest setting. Kentucky bluegrass likes to be mowed one notch lower than the highest setting. So you are pretty good to go with either one of those settings for most of the season. Just don't mow at the lowest setting unless you are seeding.

Your watering is perfect. Once a week in the heat of summer is good. Watch the grass for signs of wilting. And watering for an hour is usually good. What you should strive for is an inch of water as a starting point to see how that goes. For my sprinkler that takes 8 hours but for some it only takes 15 minutes. You can check yours with a cat food can. Time how long it takes to fill the can. That is your starting point. With my conditions, I water 3/8 inch per week in the summer unless it is really hot and dry.

Your fertilizer schedule is not bad. Do it on Memorial Day (do y'all have Memorial Day?), Labor Day (!), and Thanksgiving - all those American holidays!

does your suggested fertilizing schedule (on the American holidays) apply to both synthetic and organic fertilizers? Do you recommend applying organics earlier than Memorial day and more frequently in general?

I've read on these forums that organics can and should be applied monthly to get the max benefit. Just trying to reconcile all these opinions.

Thanks,

So what do you think about overseeding? Should I wait until the Fall?