Question
I have a lawn we seeded but used regular hay as a cover. This was a few years ago. Now the entire lawn seems to be mainly hay with grass in between. It grows very thick and high and is hard to cut. Not to mention it is straw-like and course. I now know we should not have used regular hay but it is too late. Is there a way to kill off the hay to allow the gras to eventually take over and fill in?

Answer
'Hay' could be anything growing in a field that was used for forage.  Ken, I feel your pain.  The type of Hay used for protecting Grass Seed as you know is certified to be Weed Seeds Free -- for good reason, as you've learned.

What you have now is a severe Weed problem.  Some of these are actually good for your Lawn -- perhaps there is Alfalfa or other Nitrogen fixing plants down there.  Most of it, though, who knows?

If more than half the Lawn is now 'Hay', i.e., Weeds, it is time to start over and learn from our mistakes.

Should be fairly easy to pull up all the Grass now and start a compost pile.  Then till -- EVER SO LIGHTLY -- and Seed.

Thick, healthy, MOWED Grass growing in RICH Soil has nothing to worry about.  Lucky for you, we are now beginning Grass Growing Season for new Lawns.

Do it right this time.  Start with a Soil Test -- the perfect pH, the right balance of Magnesium and Phosphorous, good tilth.  Pick a state of the art Seed with bells and whistles.

Mow it all Summer, high, as much as possible to choke out any latent Weed Seeds still lurking down there.

In the Spring, use a preemergent Cornmeal Gluten Weedkiller to keep Weeds from germinating.  Let me know if you need further advice on this.