English lavender (Lavandula angustifolia) is the most cold hardy species. Two varieties recommended for zone 5 are Hidcote and Twickle Purple. Munstead also stands cold very well, but doesn't produce long stemmed flowers. There are two French lavender varieties from a cross between L. angustifolia and L. spicata that are not quite as hardy, but might work out. The cultivars are Grosso and Fred Boutin.

In general, plants survive better in the ground than in pots. A spot sheltered from wind helps, and snow cover protects plants even better. However, perfect drainage is absolutely essential. Planting at the top or on the side of a slope is best.

Munstead does better here than Hidcote. I had very good luck with Lady when it was widely available as seed. There is a relatively new lavender that people seem to have had good luck with, but I haven't grown it and don't remember the name.

The biggest piece of advice I can give you is to check your soil pH, and if it is low, add lime. It is much easier to change the pH than to make 'perfect' drainage, particularly since frozen soil doesn't drain almost by definition.

I am colder than you and have tried a bunch of different lavenders. The one that has done best is Phenomenal which is on year 4 in my garden.

Thanks all. Any recommendations on where I could buy Munstead or Phenomenal? I usually go to box stores, and they don't even name their varieties, it's just "Lavendar". Thanks

I got Phenomenal via mail order after seeing it reviewed on the Perennials Forum, IIRC. Mine came from Wayside Gardens since they had another plant I couldn’t find elsewhere. It came in a 6pack for less than $20 I think. I only find individual plants now. While I have had mixed results with Wayside over the years, both the lavender and the clematis I got were first rate plants. Bluestone has Phenomenal also.

I will just add this, which I read in one of Carol Stocker’s Boston Globe columns: lavenders do not care for much of the soil in the greater Boston area, which she calls “blue clay.” She gardens in Milton, IIRC. I assume that this is because of the drainage requirement mentioned above. I’ve had fairly good luck growing lavender in my town, which on a geographic survey map is located right in top of deposits of sand and gravel! And indeed, when we were being hooked up to sewers a number of years ago, the trench kept trying to refill, the soil was so sandy.

So, if you do have drainage problems, perhaps amending with sand will help. I am in zone 6a, but right on the line with 5b according to people who live a bit further west.

Thanks all. I do water however until it is "established" right?

Will sand also raise the pH?

The above lavender is on its third year and I'm surprised it survived this winter with nary a blight or struggle. I grew it from seed and it is either Hidcote Superior or Ellagance (their spelling, not mine) Purple. I'll have to look through my wintersowing records to see. I sowed both, but it's possible only one type made it into the ground. They are in a raised bed so drainage is good. I think I also added something to increase pH without being too careful, like throwing some wood ash in. One "weird" thing I did do, which I learned from the Shaker village in Canterbury, NH, is add a layer of white pea gravel or small stones to sit on top of the soil. The Shakers apparently did it not only for drainage, but it help the sun reflect back up onto the lavender and keep it dryer and increase sun exposure. I have no idea if the rocks help now because the plants seem to cover the area completely, but it is possible they help in spring when they are small and waking up again during lots of rain and less sun.

I have tons of lavender, but I do not know the exact variety. It thrives here in my zone 6b garden with absolutely no winter dieback, so it may well be hardy in your zone. It self-seeds like crazy. I am always pulling up many plants every spring as weeds!

Wow Bill, so beautiful! Full sun, I assume? Thanks.

Yes it's full sun all day. Reseeds like crazy, but that's OK.

Unfortunately I could only find Spanish lavender. When I learnt it was not hardy to zone five b, I potted the plants. What is the best way to overwinter the pots? Options are unheated sun room, or either a dark unseated garage or dark heated basement. Thanks.

Unheated sunroom. It has no chance of surviving the winter in the dark.

I'm in MA zone 6a so I get your struggle
lavender constantly dies on me. The only one that's survived a winter was Dilly Dilly, hopefully that helps you. I also tend to not water it as much as my other plants

Mine is English lavender and is perfectly hardy here in zone 6B. I would wonder why struggle with other non-hardy types?