Is it safe to plant on soil that was treated to kill grass and seeds?

I would wait a few months, especially if you are planting vegetables. Those chemicals last for a long time.

It depends on what you want to plant. If you want to plant anything that is edible , I

would NOT plant it there !!! Or anywhere that you have used pesticides or chemicals. If that is the space you need that gets the right sun , then use large planters .

A pre-emergent ( kills sprouting seeds ) and an herbicide for established plants are not the same thing -- if you have the container, I'd call the 'Questions' number, or go online to see how soon you can replant the area ...

No. You need to dig out what was there or extremely overwater it to reduce and dilute the ph. This is why it is pointless to use weed killer or worst deisel: you end up needing to overwater it anyway to get the ph down anx may need add manure while it is wet.

When that is so, you are best to water down Manures (to make a diarrhea daiquiri of 32 ounce water to 8 ounce manure) and pour it on the flooded area.

No. I wouldn't plant in that area. First of all, in the future look up the lasagna method for killing grass and weeds in an area where you would like to create a garden later. For the long haul, weed killer just doesn't work. If you leave that area now, you will have weeds coming up again in no time.

What you can do now though, is use raised garden beds. I would place a layer of cardboard between the raised beds and the ground and then fill them with some good compost. I would make sure the raised beds are at least 12 inches deep. Good luck!

Possibly disagree with both. Depends entirely on WHAT was used. Roundup, for instance, is totally gone within 5 days with contact on organic matter. You likely have something different as it will not kill seeds. Still, WHAt was used, very important.