Wintering English and Lady Lavender

I purchased English and lady lavenders from your company by the plug trays in the Spring. I need to know how to overwinter them in an open field. The business I have helps the poor and disadvantaged. I mention this as funds are at a minimum therefore could you suggest inexpensive ways if possible.
I have been delighted with the quality of the plants I purchased ( which included ten or eleven trays of various plants, plus plants that were larger and some in-store product purchases). I also want to let you know the customer service I received was excellent.
I plan to have many years of purchasing from you as my business in Horticultural Therapy expands.
Thank you for any help in making a success of keeping the plants healthy and growing each year.

Thank you for letting us know that we did our job well! As for your lavenders, you have to consider the plant hardiness zone you are residing in. English lavender is able to survive zone 5 winters, but needs heavy mulching in any area colder than this. Lady lavender is winter hardy to zone 6 and will only survive in the warmest areas of Canada without lots of help. In a field, the mulching is about the only option you have. Make sure that your mulch is loose, since smothered lavender rots even if it is not killed by the frost. In individual plants I always advise people to pop a pot over the plant and mulch over that, since the pot will prevent smothering. A one foot (30cm) deep mulch may help the plant survive in one zone colder than it is rated for.
The best mulch is probably straw. Do not use leaves, since they pack down and hold so much moisture that lavender will rot. Remove all but a few inches of the mulch as early in the spring as the frost is out of the ground – again to stop rot.