University of Minnesota Extension
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One of the easiest and most popular culinary herbs to grow is the common or sweet basil, Ocimum basilicum. A member of the mint family (Lamiaceae), it is native to southern Asia and islands of the south Pacific. This tender annual is primarily grown for its aromatic leaves, used fresh or dried, to liven up numerous dishes of both Asian and Western cuisines. Basil seeds are also used in Thai foods.
Like most herbs, basil requires a sunny location that receives at least 6-8 hours of bright light per day, and well drained soil conditions. A pH range of 6.0-7.5 is ideal.
Propagation is easiest by sowing seeds directly into the ground where they are to be grown, after danger of spring frosts has passed. Sow evenly, covering with 1/4 inch of soil, and keep moist and free of weeds. Germination should take place within 5-7 days. The basil seedling is recognizable by its two broad seed leaves, each shaped like a capital D, borne with flat sides facing each other.
Once seedlings have developed 2-3 pairs of true leaves, they should be thinned or transplanted to stand 6-12 inches apart. Seeds can also be sown indoors 6-8 weeks before planting outside to get a head start on the growing season. This is especially beneficial for some of the slower-germinating varieties such as O.b. 'Purple Ruffles.'
A 2-3 inch mulch of grass clippings, straw, compost, or ground-up leaves will be beneficial in retaining soil moisture and minimizing weeds around the plants.
Depending on the amount of regular rainfall, water deeply every 7-10 days to insure the roots are receiving adequate moisture. Plants grown in containers will dry out faster than those in garden beds, and will have to be watered more frequently. Choose a container with holes in the bottom for proper drainage.
Fertilize sparingly, using a 5-10-5 commercial fertilizer once or twice during the growing season at the rate of 3 oz. per every 10 ft. of row. Use a liquid fertilizer at one half the label recommended strength every 4-6 weeks or so for indoor plants and every 3-4 weeks for basil grown outside in containers.
Begin harvesting at any time by snipping the fresh young leaves as they are needed. If whole stems are harvested, cut just above a pair of leaves. New growth will be encouraged at the cut point and should be seen within a week's time. From a culinary perspective, it is important to prune the plant periodically through the growing season to maintain succulent and productive growth. Otherwise, if basil is allowed to flower and form seed, it will become woody and yields will be considerably less. Quality will also be affected, with more bitter flavors arising. However, some of the flowers do have ornamental value, especially the purple-leafed varieties, which have pink blooms, so if your plants flower, cut some stems for a mixed bouquet.
Since basil is a tender annual, it will not survive the winter in our region. At the end of the growing season, you may choose to dig up your plants and bring them inside for the winter. If this is the case, make sure they receive plenty of bright light. Artificial lights may have to be installed and run for 10-12 hours daily since light will not be adequate indoors during the darker winter months. As annuals, basil plants will flower and die eventually, even indoors. Plan to start new seeds or buy new plants each spring.
Basil is best usedfresh. The clove-like aroma and flavor is a wonderful seasoning in both Western and Asian foods and the fresh leaves have a tender texture. However, many people use dried or frozen basil during the cold months when fresh basil isn’t available.
Leaves can be preserved by hanging the foliage upside down in small bunches and air drying in a warm, dry, well ventilated room for a week or so. Foliage can also be dried by spreading flat on a drying rack under the same conditions. Once the basil is thoroughly dried, strip the leaves from the stems and store whole or ground in an air tight container away from heat sources and bright light. If stored properly, it should keep for about a year. If any sign of moisture occurs, empty the container and repeat the drying process. Unfortunately basil leaves turn a very unpleasant brown color when air-dried. Freezing is a better method.
Freezing is another method of preserving basil, and usually results in a product with flavor more like fresh basil. Freeze whole leaves in small quantities in small plastic bags or chop up the leaves into small pieces and place in ice cube tray compartments topped off with a little water. Another freezing method is to mix ¼ cup chopped basil with 2 teaspoons vegetable or olive oil. Drop teaspoonfuls of this mixture onto wax paper-lined baking sheets, freeze, and then peel off the wax paper and store the basil mixture in plastic bags. Similarly, basil pesto can be prepared in quantity, then frozen in small containers. Omit any cheese from the recipe if you plan to freeze pesto. Whichever method is chosen, frozen herbs should be used within a year.
The traditional sweet basil, Ocimum basilicum, is the most popular variety, used primarily for culinary purposes such as pesto and tomato dishes. But there are many other varieties offering both ornamental value and unique fragrances.
Here are a few to try:
- Spicy Globe - O. basilicum, 8"-10". Use green foliage in many dishes as well as a nice edging or border because of small, compact plant size. This is a good indoor plant as it is slower to go to seed than most other types.
- Lettuce Leaf Basil - O. crispum, 15". Produces large, crinkled green leaves which have a sweeter flavor than other varieties. Very vigorous grower.
- Lemon Basil - O.b. 'Citriodorum', 12"-18". Fine-leafed plant with distinct lemon fragrance. Use in potpourri, iced teas, salads.
- Opal Basil - O.b. ‘Purpurascens’, 12"-18". A very versatile variety that has red-purplish foliage and pink flowers. Use ornamentally in most garden settings, fresh floral arrangements or herb vinegars. O.b. 'Minimum' is a compact variety.
- Cinnamon Basil - Ocimum sp., 18". This variety offers dark green shiny leaves and pink flowers. The flavor and fragrance in both foliage and flowers is very spicy. Use in dried arrangements, potpourri, vinegars and jellies.
- Thai Basil - O.b., 24"-36". An upright, well-branched plant with flavor and fragrance distinctly different from other basils. Excellent for Asian cuisine; highly decorative with purple stems and flowers.
Edited by Jill MacKenzie, Former Extension Specialist, Horticulture, University of Minnesota Extension, 6/07. Reviewed by Shirley Mah Kooyman, Adult Education Manager Minnesota Landscape Arboretum and University of Minnesota Extension, 10/07