Basil is a flavourful herb often used in pasta dishes, salads and sauces. Basil is simple to grow in your own garden, as it requires little fertilisation and is equally suited to life in the ground or in containers. Like other plants, basil is not exempt from problems with pests, disease and growing problems. One symptom your basil may experience is curled leaves.
Basil is affected by viral and bacterial plant diseases. These diseases spread through the soil and from plant to plant if an infected plant is incorporated into your garden. Symptoms of viral, bacterial and fungal diseases in basil include discolouration, wilt, rotting of the stem or leaves, growths on the plant and curling of the leaves. One particular disease that causes leaf curling is cucumber mosaic virus. Treat disease with fungicide or antibacterial and anti-fungal products from your garden supply store. Another treatment method is to remove infected plants completely from the garden to prevent the spread of disease in your garden.
Basil is an easy plant that does not require excessive fertilisation. In fact, too much fertiliser often causes basil to have an unpleasant or bitter flavour and may cause leaves to discolour, wilt or curl. However, insufficient nitrogen in the soil also causes leaf curling. Provide basil with continuous fertilisation by working compost or coffee grounds into the soil to provide slow-release nitrogen fertilisation. Fertilise basil with a liquid fertiliser every three to four weeks as an additional means of nourishment. Remove curled leaves and correct fertilisation problems to prevent further leaf curling.
Basil grows rapidly and prefers hot weather, so it needs plenty of water to keep up with its growth rate and hydration needs. Basil needs consistently moist soil to keep it at its healthiest. Curled leaves on your basil plant may be the result of either over-watering with too moist conditions or under-watering along with too dry conditions. Water your plant once or twice daily, depending on the dryness of your climate. Keep soil moist, never soggy or muddy. Insert your finger 2 inches into the soil before watering -- if soil feels moist 2 inches deep, watering is not necessary. If soil feels dry, water more frequently. Properly watering your basil helps to prevent leaf curling.
Basil is affected by pests that damage and sometimes kill the plant. Pests that infest basil include mites, thrips, aphids and beetles. These pests use piercing, sucking mouth parts to extract fluids from inside the basil plant. The result is dry, scorched-looking, curled leaves. Other signs include discolouration, wilt and dropped leaves. Treat basil for pests using insecticides or natural remedies such as hot pepper or soap sprays.