Lettuce

Lettuce (Lactuca sativa)

Other common names: 生菜, 叶用莴苣, 玻璃菜

One of the most recognisable leafy vegetables, lettuces come in a variety of shapes and colours, with flat-leaved, curly, green, and red cultivars serving as exciting options for the edible gardener. Loose-leaf lettuces do better in the tropics as the leaves have plenty of airflow, and the clear leaf seperation makes it easy to prune and for cut-and-come-again harvesting. Head lettuce is difficult to grow outdoors in Singapore due to the heat and humidity, which tends to cause the tightly bunched leaves to rot.

An annual crop, this plant is often grown and consumed under 2 months. Its rapid harvest cycle makes it useful for crop rotation.

Due to its shallow root system, these plants are a popular choice for container gardening.

Sun and soil needs:

Lettuce does best in more than 6 or more hours of indirect sunlight, or around 4-5 hours of direct sunlight. Plants do best in pots with loamy soil at least 10cm deep, or in true ground. These plants are vulnerable to root rot, so ensure that your pots drain well, and that your soil has plenty of organic matter to let the roots breathe. Keep your plants cool with mulch and plenty of water to encourage growth.

Sowing seeds:

Sow seeds individually in a seedling tray filled with potting mix or seedling mix. Lightly mist the soil until damp, once a day. Seeds should sprout within a week.

The seedlings will be vulnerable to high heat and heavy rain and are best kept in a sheltered propagation area or a shaded space with around 4 hours of partial or direct sunlight.

The seedlings may be eaten by snails or birds. Protect your young plants with a DIY cloche or netting.

Transplanting:

Seedlings will be ready for transplanting into pots or true ground when they have developed 4 or more leaves, or roughly a week or two after germination. Leave 10-20cm between each plant to encourage more growth, better ventilation, and prevent etiolation.

Growing:

Lettuce is a rapid grower and will produce more leaves if fed with high nitrogen fertilisers. Plants can be fertilised regularly once every two weeks after transplanting for a fuller crop.

Harvesting:

Plants can be harvested for leaves at any time, with younger leaves being the most tender. However, the leaves will become bitter when the plant starts to flower. Most gardeners will harvest their crop around a month and a half after sowing.

The whole plant can be harvested once by cutting the head at the base or multiple times by harvesting the older leaves as per the cut-and-come-again method.

Harvest cycle:

Propagation:

Lettuce is primarily grown from seeds.

Common problems & solutions:

Young plants have soft stems and can be completely eaten by slugs and snails. Grow seedlings till they are at least 10cm tall before planting them in true ground, or use DIY cloches or netting to protect young plants.

Caterpillars, usually from the Diamondback moth and Tussock moth, can rapidly eat all the leaves of your plant. If your plant has lots of large holes and small brown or black poo pellets scattered around damaged leaves, you likely have a caterpillar infestation. Manually remove the caterpillars by hand and protect your plants with netting.

Leaf miners are fly larvae that eat the leaves from the inside, leaving white lines or patches in their wake. Manually remove damaged leaves and use fine mesh netting to stop the adult flies from laying eggs on the plant again.

Etiolation is characterised by plants growing long and skinny, with weak stems and small leaves. The plants may also sometimes look yellowish. Plants etiolate when they do not get enough sunlight, which results in slow growth and untidy forms. To prevent this, grow plants in environments with enough light for them and make sure that each plant has enough space to prevent overcrowding.

These plants are vulnerable to sunburn in more than 6 hours of direct sunlight. Use shade netting to protect your plants or replant in a shadier spot.