Medicinal herbs were grown and dried for use in the winter.

All Heal - used to break as well as prevent fevers
Feverfew - used to break as well as prevent fevers
Lavender - digestive aid
Sage - digestive aid
Peppermint - digestive aid
Goose Grass - good for healing breaks, cuts, and lesions
Tansy
Dandelion - purgative and diuretic
Boneset - good for healing breaks, cuts, and lesions
Willow bark - used to break as well as prevent fevers
Garlic

Culinary plants and herbs were grown for use during the summer and were dried or otherwise preserved for use during the winter.
Winter savory, some oreganos, garlic, and chives would last through most winters.
Other plants such as basil, curry, lavender, coriander, tarragon, sage and rosemary had to be harvested and dried. Pink Dianthus (different from today's) were used to freshen the flavor of many Summer dishes with its clove-like flavor.

Household herbs - used to sweeten the air and alleviate pests.

Lavender - still used today to deter fleas and moths
Rosemary - good for healing breaks, cuts, and lesions
Sage
Citron - good for healing breaks, cuts, and lesions
Pennyroyal
Peppermint
Parsley

http://www.gardeningknowhow.com/herb/the-medieval-herb-garden.htm

Apothecary's Rose
Dill
Thyme
Angelica
Borage
Bee Balm
Fennel
Nasturtium

Some herbs were even grown for religious ceremonies.

http://www.suite101.com/content/medieval-herb-garden-plants-part-1-a13057
http://www.suite101.com/content/medieval-herb-garden-plants-part-2-a13059

Lemon Balm
Mint
Rue
Basil
Marjoram
Costmary (Alecost)
Roses (Rosa species)
Violets
Johnny jump-ups

http://gallowglass.org/jadwiga/herbs/smallherbs.html