Lavender and Winter Survival

We live just south of Rochester, NY, USA, the Finger Lakes region of New York. We are a zone 5.
We planted lavender this spring (Grosso, Provence, English) it is doing well at this time. We worked the ground up very well, amended the soil to the correct ph, are using the black mulch cloth that breathes and lets in some water and then used stone dust on top of the black mulch cloth to help reflect the sun and further help with drainage.
We now want to prepare for this first winter and have heard different views as to what to do. Some have said plants should do fine – don't worry. Others have said we should mulch. What is your recommendation?
If we mulch - how thick of mulch? We are in an area the last few years that have seen some early signs of spring and then it turns very cold again. Would we have to take the mulch off - and then put it back on?
It was also suggested that we use a sprinkler system and water the plants down when we suspect a very cold day - much like they do with oranges in the south.

Lavender likes to be almost dry and cool in winter. The sort of temperature fluctuations we tend to get in the Great Lakes Area is not doing the plants any good, because they might start into growth during a warm spell and then get killed wit the returning normal cold weather.
For this reason I recommend a one foot (30 cm) straw mulch. It holds the snow and prevents the rapid temperature changes that occur on barer ground. Do not remove the mulch until the danger of killing frosts is over.
I would not recommend sprinklers in time of severe low temperatures, because the water will do more harm than the cold. If the weather is forecast to be really freaky and turn suddenly very much colder, you could cover the whole bed with plastic. This will allow the temperature to drop a bit slower and not go down quite as much and the plants can adjust better. Remove plastic during the day to prevent overheating. As you can see this is a lot of trouble and would only be worth it if we get a really wild temperature swing - something getting more frequent in these times of global warming.