For the home cook there is nothing lovelier than sprinkling chopped fresh oregano and basil onto a pizza or putting a fresh bay leaf in a winter stew and sprinkling chopped parsley over the top when serving it. Many home cooks over-winter herbs in pots on a sunny window sill, but as low light levels and cold temperatures take their toll on the plants, replacement of leaves used for cooking slows and gradually fades. But with a greenhouse, you can grow enough herbs to last all winter long no matter how much you might need for dinner.
Bay leaves
If you use bay leaves you should grow your own bay bush. I have had mine for almost twenty years in a pot that is around 18″ across. The bush is nearly three-feet tall and requires very little care, only that I fertilize it once in a while and keep its roots moist. I let it dry out between watering. The only problem I find with it, is that it has a tendency toward fire blight. To keep the disease under control I prune any affected branches back to good wood as soon as I see a problem. Winter temperatures can fall as low as 40 degrees without ill effects, but try not to let it freeze or the leaves will drop.
Rosemary
I have three different types of rosemary growing in pots to ensure that I can harvest it as needed. Rosemary does not like to be dry, so you should be sure to set it on a tray of pebbles and fill the tray with water to raise the humidity around the plant during the winter months. If the plant dries out it will often die. In summer, an occasional dose of fertilizer is all it needs to keep growing. Winter temperatures can go down to 50 degrees F with occasional lower temperatures but the plant prefers a warm, moist habitat.
French Tarragon
Another herb that does not like to be dry is French tarragon. (Use only French tarragon in cooking, Russian tarragon has a different flavor.) French tarragon can only be propagated from cuttings while other types of tarragon can be grown from seed. Like other perennial herbs it gets a little fertilizer and water during summer and sits on a tray of moist pebbles in winter. I have found this herb to be a little finicky to keep going for more than three or four years.
Thyme
Thyme is one of the easier herbs to grow. I have thyme planted between the rocks on my patio where the plants have grown into huge mats. It does extremely well in a sandy, well drained, potting mix. Like the other perennials it gets a little fertilizer and regular water during summer months. It can take freezing temperatures and puts on new growth every spring.
Oregano
There is nothing quite like fresh oregano on a freshly baked pizza. That said, oregano will grow into a huge plant and self-seed, so I grow one plant outdoors and another in the greenhouse. Both plants are cut before they flower. Their leaves are easily dried after cutting. An oregano plant can survive freezing, but it loses its leaves.
Sage
Sage is another easy to grow plant that can be grown inside or outside. I grow several types of sage in my garden and in pots in the greenhouse. Sage can survive freezing but for best flavor dry the leaves and put them in a jar.
Chives
A member of the onion family, chives will grow until frost. In spring the shoots grow fast and should be harvested, chopped and frozen before the plant flowers. You can also use the flowers (chopped or whole) in salads instead of red onions.