How to Manage Hydroponic Lettuce? Key Technical Points Explained in Detail

Lettuce (var. ramosa Hort.), commonly known as leaf lettuce, also called goose lettuce, mai zai cai, or wo zai cai, belongs to the Asteraceae family, genus Lactuca. It is an annual or biennial herbaceous crop with long obovate leaves that form dense cabbage-like heads. It can be eaten raw, is crisp and tender with a refreshing taste, and is slightly sweet. Lettuce originated along the Mediterranean coast of Europe, domesticated from wild species. The ancient Greeks and Romans were the first to eat it. Lettuce was introduced to China long ago, and is widely cultivated along the southeastern coast, especially in the suburbs of major cities and in the Guangdong and Guangxi regions. In recent years, the cultivation area has expanded rapidly, and lettuce has moved from hotels and restaurants onto ordinary people's dining tables.

Main Types of Lettuce

Based on leaf growth form, lettuce can be divided into head lettuce, curly-leaf lettuce, and upright lettuce.

Head Lettuce

The main characteristic of head lettuce is that its terminal leaves form a head. The leaves are entire, serrated, or deeply lobed; the leaf surface is smooth or wrinkled; and the terminal leaves form a round or nearly round head. Main varieties include Dahu 659, Qianwei 75, Salinas, Beishan No. 3, Mamike, Bilu, and others.

Curly-Leaf Lettuce

The main characteristic of curly-leaf lettuce is that it does not form heads. The basal leaves are long ovate, with relatively long petioles; the leaf margins are wavy with notches or deep lobes; and the leaf surface is wrinkled. The clustered leaf rosette looks like a large flower. Main varieties include “Hongfan” purple-leaf lettuce, red-leaf lettuce, Lubo, Dongshan lettuce, and others.

Upright Lettuce

The main characteristic of upright lettuce is narrow, elongated leaves that grow upright. The leaf margins are entire or serrated, the leaves are thick, the texture is somewhat coarse, and the flavor is relatively poor. This variety has few cultivars, is not widely distributed, and is rarely grown in China.

How to Manage Hydroponic Lettuce?

Compared with conventional soil cultivation, hydroponic lettuce offers good quality, high commercial value, fewer pests and diseases, and no continuous cropping obstacles. In February last year, we conducted experimental cultivation of hydroponic lettuce. The static hydroponic lettuce method is simple and easy to operate, making it suitable for promotion in production. Below is a brief introduction to its cultivation and management techniques.

1. Variety Selection and Seasonal Arrangement: Lettuce prefers cool conditions. It grows best in winter and spring within a temperature range of 15°C to 25°C. Below 15°C, growth is slow; above 30°C, growth is poor and bolting and flowering occur very easily. Loose-leaf lettuce varieties are suitable for hydroponic cultivation.

2. Nutrient Solution Preparation and Selection of Cultivation Containers: For the nutrient solution formula, choose to add 600 grams of calcium nitrate, 600 grams of potassium nitrate, 350 grams of magnesium sulfate, and 150 grams of ammonium dihydrogen phosphate per ton of water. For micronutrients, use a general-purpose formula. In production cultivation, troughs or beds can be used; for home cultivation, pots, basins, or boxes can be used, as long as they do not leak water.

3. Seedling Raising and Transplanting:

1) Seedling raising: Take a seedling tray and use vermiculite as the seedling substrate. Before sowing, soak the vermiculite thoroughly with water, spread the seeds evenly on the surface of the vermiculite, then cover with a layer of vermiculite equivalent to the thickness of the seeds, and water thoroughly. At a temperature of 20°C, seedlings emerge in 5 to 7 days. After emergence, irrigate with a nutrient solution having an EC value (electrical conductivity, a key indicator in water quality standards) of 1.6 to 1.8.

2) Transplanting: Take a foam board and punch holes every 20 cm with a hole diameter of 2.5 cm, and cover the mouth of the hydroponic container tightly. Place nutrient solution in the container with an EC value of 1.6 to 1.8. When lettuce seedlings grow to 2 true leaves, carry out seedling separation and transplanting. First, wash the vermiculite off the roots of the seedlings, wrap a strip of sponge around the stem base, and then insert the seedling into the hole in the foam board. Keeping the stem base dry and well ventilated can greatly reduce the occurrence of diseases at the root-stem base.

4. Management and Harvesting: The management process for hydroponic lettuce is very simple. After transplanting, to keep the nutrient solution level stable and consistent, add nutrient solution once every 2 to 3 days, with a water temperature of 20°C to 22°C and a pH value of 6 to 6.5. When seedlings have 3 to 4 true leaves, adjust the EC value to 1.8 to 2, and continue adding nutrient solution as needed. After about 20 to 25 days, they can grow into marketable vegetables.

For home cultivation, leaves can be harvested as needed and eaten fresh to maintain freshness. In production, harvesting is generally done all at once. To visually demonstrate the characteristics of hydroponic vegetables, it is better to keep part of the pure white root system. To reduce the nitrate content in lettuce, one week before harvest, do not supplement nutrients and only add clean water.

5. Pests and Diseases: Hydroponic lettuce has very few pests and diseases. In nutrient solution hydroponics, keeping the nutrient solution clean is very important, because once root diseases occur, they spread quickly and cause irreparable losses. In addition to properly disinfecting the nutrient solution, the nutrient solution should be completely replaced once a month. In summer, aphids, red spider mites, and other pests sometimes occur, and can be controlled with the high-efficiency, low-toxicity biological pesticide abamectin preparation.