Are Weeds Halal

If you are referring to seaweed, then, yes. It is kind of sea food that is halal to eat and allowed for Muslims to eat.

If you are referring to intrusive grasses, such as crabgrass, I can see no reason why they would not be halal, but I can also see no reason why you would wish to consume them.

If you are referring to "weeds" as slang for marijuana, then no. It is haram for a Muslim to use mind-altering drugs for a recreational purpose.