I am interested in using hay as a mulch/ground cover in our row crop garden. I know it makes veg. gardens look pretty for a photo, but how practical is it? I'm concerned about grass and weed seeds, of which I already have problem. Any thoughts?

Use straw not hay . Hay has seed which straw does not.

Straw is what you want to use. (I learned this the hard way. )

Just as a bit of insurance, we learned to spread the straw out in the paved driveway for a day or two (when no rain was predicted) to allow the birds to eat any stray weed seeds which may have tagged along in the bale.

Welcome to All Things Plants, @mcm !

I totally agree with not using hay... learn from our mistakes

A good quality Bermuda Grass hay, for example, should have no seeds and is less water proof than straw.

Pork, I know absolutely nothing about farming, so consider this question is coming from a dummy. Why wouldn't Bermuda grass not have seed? My lawn is Bermuda and from June till fall, there are lots of seed heads present at every mowing. Is Bermuda grown as hay different than my lawn grass?

- Because the conscientious hay farmer cuts it before it goes to seed and loses nutritive value.

Hay I understand is a first cutting and contains all the seed heads, or 'grains' and that is nutritious for livestock.
The straw is a second cutting, of the stems part after some regrowth. (?) and does not contain matured seed heads. Therefore if you use hay, you will get lots of sprouts (weeds to your garden) and straw does not have that.
I use straw and I love it. I primarily use oat straw I buy at Lowes. I have Bermuda grass lawn and I HATE it really bad. Very invasive tough weed. Practically impossible to kill, I just try to control it at best. Even straw will have some viable seeds here and there. I would never purposely use anything that might maybe be contaminated with Bermuda seed. If you put the straw on in the fall, you may have to re-apply some in the late spring. usually spring and fall I lay some down. It looks a little 'raw' at first but in a couple weeks it settles in and looks nice. I just use mulch around the front of the house where I want a more formal look and the straw goes in my backyard.

Frilly, straw comes from grain crops such as oats and wheats -- after the grain is harvested the stems become the "straw." Hay is grown from other plants, mostly alfalfa and Timothy up here. As Porkpal pointed out, the hay is cut before the plants go to seed because it's more nutritious.

I actually think the amount of seeds in hay or straw would depend mainly on how many weeds were growing in the field and not as much whether it's hay or straw... maybe Porkpal or someone else can give us an opinion on that thought.

The local farmers in my area harvest 'grass hay' which is 2-3 cuttings of whatever our local pasture grass consists of. When we kept large animals, it was always a bit of a race to get the hay cut 'before it headed out.'

Thanks to all "repliers"! My thoughts and your answers are matching up.