Tulsi (Ocimum tenuiflorum), which is also known as holy basil, is a small, perennial shrub with either green or purple leaves, usually cultivated for medicinal purposes in India and South East Asia. Typically the leaves are dried to make either herbs or teas, some of which are used in the religious practices of Hinduism. To care for your tulsi shrub, especially if you plan on harvesting the leaves for tea or medicinal purposes, there are a few very important gardening techniques that you need to implement to keep the shrub healthy and growing.
Refresh the planting soil around the tulsi shrub with nutrient-rich soil every spring. The tulsi plant thrives in tropical landscapes, so the soil that you use in your garden must contain of these same nutrients. If you are unsure of which soil is best for your tulsi plant, ask a staff member at your local gardening store for a soil that is dense in nutrients and free from most harsh chemicals.
Water the planting soil around the tulsi shrub regularly. Ideally you will need to water the soil every other day to keep it moist, while avoiding flooding the soil. When you feel the soil, it should feel damp or muddy to the touch, but you should not see a layer of water resting on it. Remember that tulsi really needs to be grown in a warm, humid environment, so if you are not living in such an environment, you should do your best to mimic those conditions with light and water.
Trim or clean dead or dying leaves from the tulsi shrub as frequently as you notice them. Because the tulsi shrub needs to be in a moist environment, the leaves can attract some mould, in which case you need to clean the leaves by wiping away the mould with a soft cloth. Also, the leaves can become brittle from not enough water or sun exposure, in which case you need to trim them away from the shrub with small gardening shears.
Harvest your tulsi after it is fully grown (about 1 meter in height). According to Dr. Ralph Miller, co-author of "Tulsi Queen of Herbs: India's Holy Basil," this process can take several months in the right conditions.
Protect your tulsi in the winter months. When the leaves have died back, you may want to cover your plant with a tarp or plastic bag to protect it from especially cold weather. Simply put the tarp on top of your tulsi shrub and secure the bottom of the tarp or bag by bunching it together at the bottom of the shrub. This will not work for every shrub, unfortunately, especially if you live in cold climates. If you live in climates that get no snow, there is a good chance that your tulsi shrub will survive the cold, winter months, and then bloom again in the late spring.