Basil (Ocimum basilicum) is grown as an annual, although it may live for up to two years if it is not exposed to frost. It is hardy in U.S. Department of Agriculture plant hardiness zones 9 to 11, which means there's a chance it will survive winter in all but the northernmost parts of Florida.
Plants generally grow to a height of 2 to 3 feet, but there are larger and smaller cultivars. 'Genovese' (Ocimum basilicum 'Genovese') matures to 3 to 4 feet tall with spicy-sweet flavored leaves that are used to make pesto sauce. 'Pesto Perpetuo' (Ocimum basilicum 'Pesto Perpetuo') tops out around 1 ½ feet with variegated foliage.
Basil Growing Requirements
To test your drainage, dig a 1-foot-deep by 1-foot-wide hole to see how fast the soil drains before planting the basil. Fill it with water twice, and monitor how quickly the water drains the second time. If the hole empties within two hours, it drains fast enough.
Basil does well in soils with a pH between 6 and 7.5. The soil throughout most of Florida will fall within this range. At the southern tip of Florida, however, the soil pH tends to be high. Test the pH and lower it with sphagnum peat moss or elemental sulfur if it is above 7.5. Use 2 ½ pounds of peat moss per square yard to reduce the pH by 1, or from 8 to 7, or use 1 ounce of elemental sulfur per square yard, applying the sulfur one year before planting.
Mix a 2- to 3-inch layer of organic matter into the soil to improve drainage if water takes two to three hours to drain from your test hole. Composted pine bark mulch, compost, sphagnum peat moss, worm castings and well-aged cow manure are good options. A combination of different types of organic matter is best. Mix it thoroughly into the top 6 to 8 inches of soil with a shovel or rototiller.
Mix the same amount of organic matter into sandy soil to increase nutrients and help retain moisture. If peat was used to lower the pH, include the depth used when calculating how much additional organic matter should be added. Mix 4 ounces of 5-10-10 fertilizer per square yard into the soil along with the organic matter.
Containers and Raised Beds
Grow basil in containers or build a raised bed for it if the water takes four or more hours to drain into the soil. Raised beds can be made from stones or landscape timbers. They are commonly 1 to 2 feet high and filled with compost or composted cow manure.
Plant basil in containers with drain holes in the bottom. Use houseplant potting soil that contains sphagnum peat moss, vermiculite and perlite. Mix commercially packaged compost into the potting soil at a rate of one part compost to three parts potting soil to increase nutrients. Do not use garden soil in containers. It does not drain quickly enough or hold enough nutrients. Plant small basil varieties in 4- to 6-inch-diameter pots, medium varieties in 8- to 12-inch pots and large varieties in 12- to 16-inch pots. Basil can be grown indoors year round in front of a south-facing window, but it grows better outside.
When to Plant
Plant basil outside when temperatures stay above 70 degrees Fahrenheit during the day and above 50 F at night. Space them far enough apart to reach their full width with a few inches to spare. For example, if the variety grows to a width of 3 feet, plant it at least 20 inches away from other plants.
Water basil generously right after planting to help settle the soil. Spread a 3-inch layer of organic mulch over the soil to reduce evaporation. Water the basil again when the top of the soil begins to dry. Use a watering can or soaker hose.
Keeping the leaves dry helps prevent disease. Water in the morning so that the leaves will dry during the day if they do get wet. This may mean watering every day in the Florida heat, especially when the basil is growing in a container.
Fertilize in-ground basil two months after it is planted. Sprinkle ½ to ¾ ounce of calcium nitrate fertilizer per square yard around the plants. Do not let it get on the leaves. If it does get on them, wash it off right away to prevent fertilizer burn. Water the calcium nitrate into the soil.
Give container-grown basil water-soluble houseplant fertilizer every two weeks after it has been growing for two months. Use a balanced 10-10-10 fertilizer. A common dilution rate is ½ teaspoon per quart of water, but this is varies. Follow the dilution rate recommended on the package.
Indoors for the Winter
To ensure your plants survive the winter, even in Florida, bring basil indoors when temperatures begin to drop to near 40 F. Simply carry container-grown plants indoors.
Cut basil plants growing in the garden down to a height of 3 to 4 inches. Use sharp scissors or pruners that have been sterilized with household disinfectant and rinsed off to cut basil. Dig up the plants with a dirt shovel and pot them up to move them indoors.
Set the basil in front of a south-facing window where it will get direct sunlight. Water when the soil begins to dry and give them 10-10-10 houseplant fertilizer once each month.