For a successful harvest, you need to begin with the right time to plant the seeds. Planting your seeds in late spring to early summer will avoid seasonal frost which is damaging to the basil plant. Typically, exposure to temperatures of 50 °Fahrenheit or 10 ° Celsius or below is too cold and harmful. Ideal conditions for its growth are 70 ° Fahrenheit or 21 ° Celsius under six hours or more of direct sunlight. The planting can begin indoors about a month prior to the last cold frost of the season. When there are approximately three set of leaves, ordinarily six to eight inches in height, you can begin to harvest. Cut the top set of leaves keeping the others sets in tact. If any flowers begin to show, cut them as soon as possible. Flowering will make the basil bitter and keep new leaves from growing. The night prior to cutting, water the plant heavily allowing for more of its oils to reach its optimum. The next day, harvest them in the morning before it gets hot outside. Remember to cut the new set of leaves right above the leaves you're leaving on. With proper harvesting, the basil plant will keep growing and producing new leaves. As annual plants, basil will last only until the following frost season.
Wilting, stunt growth, loss of leaves, yellowing, browning of leaves or the stem can be the cause of several of the plant’s diseases. Diseases can come from fungus, mold and bacteria. Many of the diseases can be attributed to soil being overly watered or not drained sufficiently. Once this occurs, the soil and the plant itself should be removed and new seeds should be planted in a different location or soil. Other forms of damage to the basil plant can come from root rot, aphids, slugs, thrips and lack of nitrogen.