The Scandinavians grew hemp not ganja. At least 2000 years ago, long before the Vikings. What's interesting is the Vikings did not use hemp for rope. They used trees.
If I remember correctly they didn't use it for their masts either but I don't have the time to look for sources. It could be the hemp was too valuable, it was used for linen, stuff like blankets, clothing, etc.
It certainly would have been the European type of ganja, cannabis sativa sativa, not the drug type. Medicinal and food but not a good buzz. Vikings and other Europeans didn't smoke, no pipes have been found until after Columbus brought back tobacco. (this is a thread of it's own-lots of arguments but nothing conclusive. A lot of articles talk about a Scythian bong but I believe it's nonsense-like I say another thread) I can't remember if Inuit smoking is mentioned by the Greenland settlers. I think it might have been but once again I have other stuff to do right now. It's worth looking up.
What ancient peoples did do was vaporize hashish and ganja. Basically hot knife it and hit the smoke although it was more complicated than that. Or simply decarboxylate and eat it. The Vikings certainly had contact with the Middle East and north Africa, areas where drug strains are grown and could have imported it. And surely they were well-aware of the medicinal properties of their own strains of cannabis. Likely be more discoveries in the future adding to our knowledge of the subject.
"In addition to the theory of ritual use of hemp in Viking times or earlier, it is prudent to consider another, more mundane, theory: the hemp seeds were placed in the pouch of the Oseberg Queen for their rarity. These were highly prized seeds of an exceedingly useful plant, as yet rare in the north. The hemp seeds were valuable for their promise of better cordage and more durable textiles. Such a theory does not, of course, exclude the possibility that hemp may also have had ritual uses." https://vindheim.net/hamp/hemp.html
We started using hemp as soon as we started trading with Europe... And by trading I mean plunder and raze ;p no we did trade, we have a few Arabic artifacts in our museums that were obviously paid for as we still have the receipt on the runic sticks we found next to it. (the fact that we saved our receipts on wood really tells you a lot about the return policies of the time)