Well you are too late to start a renovation this year. You could overseed (still a bit late this year), but it will not take over your existing lawn. It will fill in bare spots, but it won't displace existing grass. In terms of picking the right cultivar(s), you should consult the ntep results (www.ntep.org) to see which ones perform best in your area. Also you will be better off planting a blend, not a single cultivar. The current practice is using a compact midnight, compact, and compact america, but there are other types you could use such as aggressive, mid-atlantic, etc. My advice would be to get a soil test (logan labs) and wait till next summer. That will give you plenty of time to get your soil up to snuff.

I'm closer to the zone you are in and I grow more than a dozen lavenders of different types from munsteads to grosso to french lavenders. I haven't suffered a loss yet. It's ideal to replace lavenders after 3 years only to keep it looking fresh, but I've kept my plants for longer. Spanish lavenders or any of those lavenders that are considered butterfly lavenders will not survive our zones. They do fine in zone 8 but not in colder areas. I have managed to root new lavenders this season which I am proud of. Cold zone types lavender thrive in the cold zones and not so well in warmer zones. Best check with the website of Richter Herbs for the list of lavenders and their zones. In my opinion do not remove or prune your plants now simply because winter is coming and those dying branches will provide winter protection to it's very center. Once that plant gets covered up with snow it will provide a form of insulation which will protect it through winter. Next spring when the snow has totally melted away and there is no longer any danger of frost, start pruning. Fresh new growth will start from its center. I can only guess why your plants are suffering die backs, one is that we've had too many wet rainy weather. Lavenders like being on the dry side,otherwise they are susceptible to fungus or root drowning. It this is the situation with your plants, perhaps next season you should transplant them to higher grounds or simply mound the area so it's a bit higher and won't get flooded.

I've given up on lavender in the ground. I now grow it in a large clay pot that I can move back under the porch roof if we're having a particularly rainy season and control the water it receives. I used to have one growing in the ground, at my old house, and it sulked and did nothing for 3 years until we had a summer of drought (summer of 2007 in central North Carolina) and it took off and flourished. Lesson learned. I only water the lavender in the pot occasionally. Even after first planting it, it didn't get daily watering. I kept an eye on it and only watered it when it showed signs of wilting.

Well I ripped them all out of the gardens and started over with another batch from another company. I did all of my gardens and my vegetable crops from seed (I usually do) and everything else is beautiful and thriving so it was definelty the seeds I purchased. Even my rosemary looks great....oh well, it did give me an excuse to go do a bit more planting and I even found a few new additions to add to my front garden. I will be contacting the company I purchased the seeds from I even had a packet left over that I decided to stick in the green house and grow away from everything else just to be 100% positive that it was the seeds and nothing else but considering it's the one and only thing that turned into these plants that I've never seen before and are nowhere else on my property, I'm pretty sure I've narrowed it down to them lol