Perennial Herb Culture

Perennial herbs are generally the herbs with woody stalks that survive year after year.  In milder climates some soft herbs can survive for more than a year, such as chives.  Primarily the perennial herbs people think of are rosemary, lavender, thyme, oregano, sage, the mint family, and marjoram.  There are others but the culture of these plants is pretty similar between species.  Personally I don't recommend starting these plants from seed, the seeds are incredibly tiny, and a bit finicky to get started.  Plus they are available as starts everywhere and aren't terribly expensive.

Perennial herbs need a sunny spot that won't be a swamp during the wet season.  They manage pretty well in my area which is basically a temperate rain forest, but if they are in a depression and get too much water with too little drainage they can die.  I have never had a pest problem or disease problem with these plants.  In fact they have strongly scented oils that can act as repellents to some pests, and at the same time most produce a flush of flowers in spring or summer that attract many pollinators.  These herbs are a great addition to any garden, attracting bees and butterflies, smelling fabulous, keeping out pests.  They don't require any fertilization so long as they are in moderately fertile soil to begin with.  Adding nutrients early in the spring can improve the abundance of fresh growth in the springtime; but don't add more after June since they are finished with most of their growth at that point.

You can plant them in pots or in the ground around your garden, I wouldn't plant them in among your annuals though as planting new annuals each year could damage the roots of the perennials, and the perennials will spread quite a bit over time leaving your no room for the annuals after a few years.  If you put them in pots make sure to move them to a warmer spot during the winter.  I have never lost a perennial herb to frost when they're in the ground, but pots are not as insulating and I often have to replace potted herbs the next spring.

Pots of perennial herbs between vegetable beds.

Rosemary, thyme, sage, oregano and marjoram are all Mediterranean herbs; they are comfortable in hot, cool, dry or moist conditions; they will appreciate both thick clay soils and sandier soils.  In fact, I don't think I've met a soil they wouldn't grow in.  Mints on the other hand prefer a cooler spot with more moisture, sandy soil doesn't suit them well.  Different varieties of these herbs will grow in different ways also.  If you're looking for a ground cover an option to consider is a creeping or spreading version of rosemary or thyme, or a standard version of oregano.  All of these will stay low growing and spread over an area, they smell lovely and produce a sprinkling of tiny purple flowers in spring and summer.  Choosing variegated, or odd colored varieties can add some excitement as well, like lemon thyme with it's yellow and green splashed leaves, or purple sage.  For culinary use smell or taste the leaves of the plants before buying them to ensure they have the flavors you want as well as the look, woolly thyme for example is a spreading attractive ground cover but it is not as flavorful and therefore does not make a quality culinary herb.  No one will mock you for nibbling the plants at the nursery, I promise.
If you are looking for more upright growth in your herbs (for use as a back row with a fronting of bulbs or annuals, or something similar) chives grow a lively bunch of bright green onion-like tops, sage comes in a variety of colors and has a silvery fuzz to it's leaves, a standard (non-spreading) rosemary can reach 4 feet tall and act as a hedge, lavender stays fairly small and makes a great perennial border, and most varieties of mint spread by underground runner and stand up to 18 inches high.

All of these herbs can be cut fresh with a pair of scissors and added to foods, teas, or used as fragrance.  They can also be dried.  To dry herbs hold a bunch of stems in your hand no bigger than you can wrap your index finger and thumb around (if your bunch is too large the center may not get adequate air flow and can mold), tie the ends together with a string, hang in a cool, dry place where they will get ventilation.  Under the eaves of your porch, on a clothesline strung across your laundry room, wherever you can find the space.  I hang my bunches from my pot rack over the island, if my stove were underneath it I wouldn't hang them there because the heat and moisture coming off the stove could ruin the herbs.  Let them dry like that for a week or more, until the leaves are crisp and crumble under your fingers.  If in doubt about whether they are dry enough, just let them hang longer until there is no doubt.  Once they are totally dry you'll want to store them in airtight containers; either plastic bags stored in the freezer or in spice jars in the cabinet.  Either way you will save a lot of space by stemming the herbs and giving them a quick grind with a mortar and pestle or spice grinder. you can continue to hang your herbs in their bunches but they will lose flavor faster and can get a build up of dust on them if left for long.

My favorite way to deal with my dried herbs is to throw together some Italian seasoning, one of the spice mixes I use most often.  First I get my herbs all prepped for putting in jars or the freezer, then just mix together  roughly equal parts rosemary, thyme, oregano, basil, and marjoram.  Then store in a glass spice jar labeled Italian Seasoning.  If this blend isn't to your taste you can also add in savory, or red pepper flakes if you prefer it a little spicy, some people also add garlic, onion, or parsley.  I prefer to keep it a simple blend and add those extras only for certain dishes, or if I have no fresh onion or garlic.

20 year old rosemary at Dad's, rhododendron behind.

Some other great ways to use these plants include: lavender sachets, dried catnip for pets, herbal soaps and lotions, potpourri, rosemary barbecue skewers, sage smudging, teas, mint sprigs in drinks, and medicinal tinctures and teas.