What are the methods to prevent leggy growth of summer vegetable seedlings?

The main causes of leggy growth in seedlings are insufficient light and excessively high temperatures, especially when nighttime temperatures are too high, as excessive respiration consumption makes it even more likely to occur. In addition, excessive nitrogen fertilizer and water, overly dense sowing, and delayed transplanting can also easily cause leggy growth in seedlings.

I. What causes leggy growth in summer vegetable seedlings?

① The period most likely to produce leggy growth and cause serious damage is from emergence to the cotyledon unfolding stage. At this time, leggy growth is mainly due to overly dense sowing and failure to remove the covering promptly after emergence, which makes the seedlings too crowded.

② Failure to lower the temperature promptly after emergence can also easily cause excessive elongation of the hypocotyl, resulting in leggy growth.

③ From the cotyledon unfolding stage to the 2-3 leaf stage, failure to thin the seedlings in time, or excessively high temperatures combined with failure to prick out (transplant seedlings into pots) in time, makes the seedlings overly crowded and causes leggy growth.

④ After the pricking-out recovery stage and before field planting, continuous rainy weather, excessively high soil and air humidity in the seedbed, and excessive nitrogen fertilizer in the nutrient soil, combined with failure to ventilate and provide light in time or to space out crowded seedlings, can also cause leggy growth.

II. Methods to prevent leggy growth in seedlings

① Sowing density should not be too high, to avoid crowding of seedlings after emergence. For solanaceous vegetables, for example, 2-3 sq m of sowing bed is generally needed per mu of field, with 15-25 grams of seed sown. At the same time, once about 30% of seedlings have emerged, remove the ground covering promptly.

② Thin the seedlings, prick out, and field plant in time. After emergence, solanaceous vegetables should be thinned in time, generally 2-3 times; when the seedlings reach the “two leaves and one heart” stage, they should be pricked out, with the pricking-out density controlled at 120-130 plants/sq m.

③ Strengthen ventilation and light exposure, and control temperature and humidity. After seedling emergence and before pricking out, and after pricking-out recovery and before field planting, ventilation and light exposure should be carried out to lower temperature and humidity, strengthen low-temperature hardening, and control excessive growth of seedlings.

④ Carry out fertilizer and water management reasonably. In preparing nutrient soil, attention should be paid to the amount of phosphorus and potassium fertilizer and the amount of nitrogen fertilizer should be controlled. In the seedbed, strictly control water and topdressing; when topdressing is needed, nitrogen fertilizer should not be applied alone.

⑤ Space out seedlings in time. About 20 days before field planting of eggplants and cucurbits, seedlings often become overly crowded. At this time, the seedlings should be moved appropriately so that large and small seedlings are separated, and the living space of each plant is expanded.

⑥ Control leggy growth with chemicals. Once leggy growth occurs in seedlings, in addition to taking the above measures, you can also spray with 0.2% Bordeaux mixture (equal amounts formula), or spray with 50% chlormequat at 2000-2500 times dilution.