My herb garden at Humlegård
I love growing herbs in my gardens - I mean who doesn't? - but as the winters are so severe here in Finland a lot of herbs that overwinter happily in other Scandinavian countries just won't make it through the winter here. Climate zone maps aren't entirely reliable, as the survival of plants not only depends on the temperature but also on snow depth and frost. During a rainy winter they don't get a protective snow cover that would see them through, and there is nothing they hate more than rain turning snow into ice combined with a really bad frost! For the most part, leafy herbs that are perennial in other countries can be treated as annuals along with the true annuals such as basil, coriander, parsly and dill. This means that come spring, my herb garden has large bare patches and I need to redo it all again. Most herbs like a sunny spot with lush but well drained soil. The soil in my herb garden is naturally sandy, so I add compost every year to slowly build it up to a nice but well drained loam.
In my gardens, the only culinary herbs I can truly depend on to thrive is oregano (Origanum vulgare), marjoram (Origanum majorana L), lovage (Levisticum officinale) and various mint varieties. The oregano spreads slowly by seed all over the garden, and turns up in the lawn or in sunny borders much to the delight of bees and butterflies, and even if the marjoram freezes and dies down, it will always return and form slowly growing soft mounds with sweet pink flowers in late summer. The mints are so invasive that I have banned them from my borders, and grow them in pots like annuals instead. Because they are in pots they don't survive the winter, but after having learned my lesson battling chocolate spearmint that took over a whole border I don't mind replanting them each year.
Lavender is difficult to overwinter in my garden, so although I always get a few plants for summer I tend to substitute it in the borders with hyssop (Hyssopus officinalis) which has much the same growth habits and colour. I find charming that in old superstition it used to be believed that hyssop prevented accidents, so I tend to use it all over in the gardens. Luna is crazy about the catnip (Nepeta cataria) and although I don't use it as a herb I do grow a lot of it in the gardens.
Other herbs will cope with moderately cold winters especially if covered with a dry mulch and perhaps some conifer branches. Sage (Salvia officinalis) is a great favourite of mine, and always has a spot in my garden regardless of wether it managed to overwinter or wether I had to replant it in spring. It is hardy down to -10 °C if placed in a well-drained soil with a dry mulch around the roots for winter. In my garden though, they may survive a few years but then invariably we get a really cold winter with - 20 °C and they all die off. The same goes for Lemon balm (Melissa officinalis). It may return yearly for a long time as it is hardy until just about - 20 °C, and then suddenly it just gets offended by the weather and gives up the ghost. Happily lemon balm is a great self seeder, so even when it has died during winter it will often leave offspring scattered around. French tarragon never survives the winter, so instead I grow Russian tarragon. The flavour of the French tarragon is far superior they say, but I must admit to being partial to the Russian one that continues to thrive regardless of winter chill.
In autumn I love to dry big sways of my favourite herbs, and smaller batches ot the others. Although it is melancholy to find the summer is over, it is at the same time such a cozy thing to do to pick the different herbs and tie into them into bundles and hang the bundles in the lamp over the kitchen table to dry. I do have an air-dryer, but after a few seasons of experimenting I have found that actually the herbs keep both colour and flavour better when dried the old fashioned way. Then I store them in glass jars on the bookshelf - well obviously the bookshelf is the natural place to store them! - contrary to popular of advice which is to keep herbs away from light in paper bags. I tend to use my whole supply within a year so I'm not worried about a loss of colour or flavour.