Hi, Well the key here is knowing what type of lavendar you have. English lavenders such as Munstead or Hidcote can withstand zone 4 winters if planted in a spot that drains well (they like a sandy soil). And, if they have time to establish a good root system before fall hits. I would not plant one if you expect freezing temps within 8 weeks or so. If, on the other hand, you have a French or Spanish lavender, they will not overwinter in your zone. You could try to grow them on a sunny windowsill through the winter, but lavendar isn't the easiest plant to keep alive in a centrally-heated home. If you like you can check out the lavendars in our Plant Encyclodia on this website to figure out what species you have.