Detailed Explanation of Standardized High-Yield Cultivation Techniques for Spring Celtuce
Celtuce, namely stem lettuce, has a crisp and tender fleshy stem with a delicious flavor. It can be stir-fried, served cold, blanched in soup, pickled, and more, making it a fine vegetable much favored by consumers. Celtuce, also known as stem lettuce, is a variety of the lettuce species in the genus Lactuca of the Asteraceae family that can form a fleshy tender stem, and is an annual or biennial herbaceous plant. Also known as stem lettuce, asparagus lettuce, green lettuce, and celtuce. Harvest period: January to April. Native to Central or North China. The above-ground stem is edible, with white-green stem skin; the stem is crisp and tender, with young tender stems being emerald green and turning white-green upon maturity. The main edible part is the fleshy tender stem, which can be eaten raw, served cold, stir-fried, dried, or pickled; the tender leaves are also edible.
Morphological Characteristics of Celtuce
The stem looks like concentric rings, resembling a bamboo shoot. It has a taproot system; after transplanting, numerous lateral roots develop, shallow and dense, mainly distributed in the 20-30 cm soil layer. The stem is shortened. Leaves are alternate, lanceolate or long ovate, etc., with colors ranging from light green, green, dark green, or purplish-red; leaf surfaces are flat or wrinkled, with entire or notched margins. The shortened stem gradually elongates and thickens as the plant grows; after flower buds differentiate at the stem tip, the stem thickens while the flower stalk elongates, forming a club-shaped fleshy tender stem. The flesh color is light green, emerald green, or yellow-green. It has conical capitulum inflorescences with pale yellow flowers; each inflorescence has about 20 flowers, self-pollinating, though cross-pollination sometimes occurs. The achene is dark brown or silvery white, with pappus attached.
Problems in Spring Cultivation of Celtuce:
1. Bolting (known as “cuan”): In the mid-growth stage, the fleshy stem becomes slender, internodes of leaves elongate, leaves become thin and small, the outer skin is thick with little flesh, and edible value is low; it easily bolts and flowers. This phenomenon is commonly called “cuan” (spindly bolting). The causes of “cuan” are roughly the following four: first, insufficient water supply and dry soil; second, insufficient fertilizer supply and poor vegetative growth; third, excessively high temperature, high respiration intensity, excessive nutrient consumption, and low dry matter allocation rate to the edible portion; fourth, excessive watering.
2. Cracking: In the late stage of fleshy stem expansion, the fleshy stem splits longitudinally, reaching deep into the middle of the stem; the split area is yellow-brown, prone to rot, reducing edible value. Causes of cracking: first, it is related to variety; second, it is related to uneven water and fertilizer supply, alternating drought and waterlogging, especially when the fleshy stem is mature and the outer skin has already lignified; at this point, heavy watering causes the fleshy stem to suddenly expand, and the epidermis cannot expand accordingly, resulting in cracking.
3. Premature bolting: If spring celtuce is transplanted too late, it is affected by high temperature and long daylight, rapidly differentiating flower buds and bolting to flower. In addition, transplanting oversized or spindly seedlings also easily leads to premature bolting.
Standardized High-Yield Cultivation of Spring Celtuce
In response to the above problems in spring celtuce cultivation, we should adopt the necessary high-yield cultivation measures.
1. Variety Selection: Choose varieties that are not prone to cracking. Generally, purple-leaf celtuce has high water content and high yield but is most prone to cracking; green-leaf celtuce cracks relatively less.
2. Timely Sowing: Sow as early as possible so that the root system and leaf rosette fully grow under relatively low temperatures, accumulating more dry matter for the rapid expansion of the fleshy stem. In our region, greenhouse sowing is generally done from early to late February. If sowing is too late, during the stem expansion period, high temperatures cause high respiration intensity, making it prone to “cuan”.
3. Raising Strong Seedlings: To cultivate 667 sq m (1 mu) of celtuce, a seedbed area of 15 sq m is needed, using 50 g of seed. The sowing bed soil should be prepared in advance as nutrient soil. The nutrient soil ratio is: 7 parts soil that has not previously grown vegetables, 3 parts high-quality decomposed organic fertilizer, plus inorganic fertilizer, mixing 50 g of compound fertilizer per cubic meter, thoroughly mixed and sieved. Then spread the nutrient soil evenly into the sowing bed, generally 6-7 cm thick, using about 100 kg of nutrient soil per sq m.
After the sowing bed is prepared, sow immediately. Before sowing, treat the seeds: first air-dry the seeds for 2-4 hours, then soak in clean water at 20°C for 3-4 hours, rub clean and drain the water, then sow. Alternatively, place the soaked seeds in a 15°C-20°C environment for germination; after 2-3 days when sprouts are uniform, sow.
The sowing method generally uses broadcasting. On the leveled bed soil, water thoroughly before sowing; after the water infiltrates, mix the seeds or sprouted seeds with moist fine sand at 4-5 times the seed volume, evenly broadcast onto the bed surface, cover with 0.5-1 cm of fine soil after sowing, and lay plastic film flat after covering soil to help retain heat and moisture. At 15°C-20°C, when most seedlings push through the soil in 1-2 days, promptly remove the plastic film.
After sowing, control the daytime temperature at 20°C-25°C and nighttime at about 15°C; seedlings emerge uniformly in 3-5 days. After emergence, maintain daytime temperature at 18°C-20°C and nighttime at about 12°C. When seedlings have 2-3 leaves, transplant them into a cold shed at a spacing of 5-7 cm. After transplanting and recovery, spray 1-2 times with foliar micro-fertilizer, and spray chlorothalonil and thiophanate to prevent disease. Water management follows the principle of keeping the soil moist and not watering unless dry. Too dry or too wet easily causes seedling aging or spindly growth.
4. Transplanting: Celtuce has a well-developed root system, dense root mass, shallow roots, and poor absorption capacity, so it needs more organic fertilizer. Generally, apply over 5000 kg of high-quality organic fertilizer, 50 kg of diammonium phosphate, and 15 kg of potassium sulfate per 667 sq m as base fertilizer, then prepare the land and make beds 1.2 m wide.
From mid to late April, when seedlings have 4-5 true leaves, transplant promptly, with a row spacing of 40 cm and plant spacing depending on variety, generally 25-30 cm, planting 4 rows per bed, generally about 6000 seedlings per 667 sq m.
The day before transplanting, spray water on the seedbed to moisten the bed soil; when digging up seedlings, carry as much soil as possible and minimize root damage. Since the outdoor temperature is relatively low at transplanting time, choose warm, sunny, windless weather after a cold spell. Plant at a depth where the roots are fully buried in the soil; do not plant too deep and bury the heart leaves. Press the soil slightly firm so the roots are in full contact with the soil.
5. Field Management After Transplanting: After planting, control water for 2-3 leaf rings to encourage seedling establishment, promoting root development and rosette leaf development. When the heart leaves are level with the rosette leaves, the stem begins to thicken; water and apply quick-acting nitrogen and potassium fertilizer, promptly shifting from “control” to “promotion”. This irrigation and fertilization must be timely; too early or too late is unfavorable to the growth of the fleshy stem. After watering begins, stem expansion accelerates, and water and fertilizer needs increase; water whenever the surface is slightly dry, watering evenly and in moderate amounts, strictly avoiding flood irrigation. When the field can be walked on, shallowly loosen the soil to break up compaction; combined with watering, apply additional fertilizer 1-2 times, applying about 20 kg of urea per 667 sq m each time. Do not apply too much fertilizer to prevent stem cracking.
6. Pest and Disease Control: Through observation over the past two years of cultivation, the main diseases of celtuce in our region are downy mildew and leaf spot, which can be controlled alternately with chlorothalonil, mancozeb, thiophanate, and propamocarb aqueous solution.
The main pests include aphids, whiteflies, lettuce winter noctuid moths, and red spider mites. For aphids and whiteflies, use imidacloprid and methomyl. For lettuce winter noctuid moths, use trichlorfon, deltamethrin, and Bt emulsion. For red spider mites, use amitraz and fenpropathrin.
7. Timely Harvest: The appropriate harvest time is when the top of the main stem of celtuce is level with the leaf tips of the highest leaves; at this point, the fleshy stem has fully expanded and is crisp and tender in quality. For staged harvesting, the apical growing point can be removed to prevent “cuan” or hollow aging. However, the interval should not be too long. Also, if slight cracking is found in celtuce, harvest and market early. Generally, the yield per 667 sq m is 2500-3000 kg.