Originally posted by electricdawn:

The most effective way for me to fight growths is to wait for them to start shooting, then dodge sideways to evade them. I then run in using their recovery down time to kill them quickly. They're completely helpless during that (very) short time.

You also can prevent them from spawning again, by just placing a camp fire right at the border of the tar pit.

This is your answer right here.
FYI, Growths will respawn even from a drained Tarpit. There can be up to 7 in a fresh one but after you kill those, I've only seen them spawn in pairs.
For dealing with Growths:
1. If there are more than two, do not directly attack. Use your bow from a distance and try to get a height advantage or leave them alone. You can also try to lure any Lox in the area over to the pit and have them fight it out. Growths hate everything.
2. Like electricdawn said above, circle around them or strafe to the side when they shoot the tar gobs at you. They will miss. When the attack is over, rush the Growth and kill it.
If you're fighting 1 on 1 and you get tarred, do NOT run away, press the attack and kill the Growth, do not allow it time to attack you again.