Hyssop, botanical name Agastache foeniculum and also known as lavender hyssop, anise hyssop and fragrant giant hyssop, is an annual herb that grows 3 feet tall. Its flower spikes rise above its foliage and have multiple clusters of tiny purple flowers that can be used in herbal teas and to season breads and muffins and other baked goods that need a light licorice flavor.
Native Growing Conditions
In the north-central United States, its natural habitat, hyssop grows in open, sunny areas. It favors wooded areas with fairly dry soil. It also can be found growing along the shores of waterways such as rivers, creeks and ponds.
Growing Hyssop as an Annual
You can grow hyssop as an annual herb outdoors anywhere in the United States. If you purchase seeds online or from a catalog, start them in an area that is protected from frost about two months before your final spring frost. Do not bury the tiny seeds---instead gently press them into the soil with your palm. Transplant 4-inch-tall young plants to a sunny spot in your garden that has any type of soil--- because it is a wildflower, it's not picky about the soil in which it grows. Even rocky soil is suitable for hyssop. It will perform well with little care all summer and then fall frosts will kill it.
Hyssop does nicely as a potted plant and will add fragrance and color to decks, patios and terraces. You can use any type of potting soil for hyssop. Choose a medium-sized decorative pot with a drainage hole if you have one plant, or purchase a larger pot for multiple plants. If you want to keep your hyssop from winter freezes, move the container indoors before Jack Frost arrives in the fall. Keep it fairly dry all winter---watering every two weeks should be sufficient to keep it alive. Be sure to give it some sunlight during its captivity indoors and you might be able to enjoy the same plant for another summer season.
Allowing Hyssop to Naturalize
When you allow a plant to naturalize, you'll end up with "wonderful weeds" that you won't want to pull out. Hyssop's flower spikes will form seeds if you don't cut them, so let the flowers turn brown and drop their small seeds to the ground and you might be pleasantly surprised the following spring when you find lots of baby hyssop plants popping up where last summer's plants once stood. Because hyssop belongs to the large mint, or Lamiaceae, plant family, you might suspect that it could become invasive, as some of the mints tend to become. However, hyssop has not been reported to be as invasive as some of the mints. If you get too many plants for the area you have designated as their home, pot them up and give them to friends as lovely green gifts.
Companion plants are those that "like" each other and seem to grow to their fullest potential when you grow them near other plants with which they are compatible. Hyssop is a friendly companion to grapes and cabbage---when you grow it next to cabbage, it can help to deter the destructive cabbage moth. Hyssop and radishes are not good companion plants, so avoid growing them near each other.