Causes and Control Methods of Buttoning and Yellowing in Broccoli

Broccoli is an annual or biennial herbaceous plant native to the eastern Mediterranean coastal region. It is cultivated on a small scale in China, mainly for use in Western cuisine. Broccoli is rich in nutrients, containing protein, sugars, fats, vitamins and carotene, and ranks first among vegetables of its kind in nutritional content, earning it the title "crown of vegetables." It is a variety of the cabbage species in the Brassica genus of the Brassicaceae family, grown for its green flower heads as the product. It originated in the Italian region along the Mediterranean coast of Europe and was introduced to China at the end of the 19th century.

Growth Habits of Broccoli

Light

Broccoli is not very demanding in its light requirements, but it prefers ample light during growth. With sufficient light, the plants grow robustly and can form a strong vegetative body, which favors photosynthesis and the accumulation of nutrients, and makes the flower heads compact and dense with a fresh green color and good quality. Excessively strong sunlight in midsummer is also unfavorable to the growth and development of broccoli.

Temperature

Within the range of 5—20°C, the higher the temperature, the faster broccoli grows and develops. The optimum germination temperature is 20—25°C, and the optimum growth temperature during the seedling stage is 15—20°C. Broccoli is highly cold-tolerant and heat-tolerant. The optimum growth temperature during the rosette stage is 20—22°C, and the optimum temperature for flower head development is 15—18°C. When the temperature is above 25°C, the quality of the flower head tends to deteriorate, but as long as it is not damaged by freezing, the flower head can still grow slowly at low temperatures of 5°C or even below. Different varieties and different seedling ages differ considerably in the temperature required to complete vernalization, so the selection of varieties is very important for year-round cultivation.

Water

Broccoli requires a relatively large amount of water throughout its growth process, especially during the period of vigorous leaf growth and flower head formation, when water shortage must be avoided. Even short-term drought will reduce yield. Rainy conditions during the seedling stage or excessively high soil moisture can easily cause diseases such as black rot and black spot. During the flower head formation stage, the soil moisture needs to be about 70—80% of field capacity to meet the growth requirements.

Soil

Broccoli is not strict about soil conditions, but overly poor soil leads to poor plant development and low yield and quality, while excessively fertile soil can cause loose flower buds and hollow flower stalks. Broccoli is suitable for planting in loam and sandy loam with good drainage and irrigation, a deep plow layer, loose and fertile soil texture, and strong water and fertilizer retention. It adapts to a soil pH range of 5.5—8, but 6 is best. Broccoli requires sufficient fertilizer throughout its growth process, with an N, P, K ratio of 14:5:8. During the seedling stage, the demand for nitrogen is relatively high, and after flower bud differentiation begins, the demand for P and K increases relatively. Note that during flower head development, broccoli also has a relatively high demand for trace elements such as boron, molybdenum and magnesium, so applying an appropriate trace-element foliar fertilizer before budding will significantly increase yield and quality.

Causes and Control of Buttoning and Yellowing in Broccoli

During cultivation, broccoli often develops fuzzy flower heads or forms buttoned heads, and some flower heads become loose, with buds withering or yellowing. When this occurs, it seriously affects the edible value and marketability of broccoli.

Causes of buttoning and yellowing in broccoli. Broccoli is suited to summer and autumn cultivation. When cultivated in early spring, its early growth period is in a low-temperature period. Although the plants grow slowly, low temperatures favor flower bud differentiation, so budding occurs early and small flower heads are easily produced. However, in the later growth period, when it enters a high-temperature period or the greenhouse temperature is too high, flower bud development is inhibited, and abnormal flower heads such as fuzzy heads and buttoned heads easily appear. When the temperature rises near the flower head harvest period, the flower head grows and develops quickly; if not harvested in time, the buds become loose and tend to yellow, especially when daytime temperatures are too high, causing the flower head to wither and yellow. Long storage time also easily leads to the above conditions. The disease is more severe in off-season cultivation.

Control methods for buttoning and yellowing in broccoli:

(1) Choose mid-early maturing varieties or early maturing varieties that are not very sensitive to low temperatures in the early growth period, such as Luling, Shanghai No. 1, Ludi, Qinglu, Zaoshenglu, etc.

(2) Sow at the appropriate time. If sown too early, because the temperature is low after transplanting, the plants undergo flower bud differentiation upon encountering low temperatures; at this time, nutrition is insufficient, with few and small leaves, leading to early budding and small flower heads. If sown too late, the temperature rises rapidly, and the flower bud development period coincides with a high-temperature period, which easily causes high-temperature injury and produces buttoned heads.

(3) To cultivate strong seedlings, temperature management is the main factor. After sowing, keep the night temperature above 12°C and the daytime temperature below 30°C. Transplant at the appropriate time when there are 5-6 true leaves; if too late, the seedlings age and the flower heads are small. Plant about 3,000 plants per 667 sq m.

(4) For those whose harvest period falls in a high-temperature stage, be sure to harvest at the appropriate time, and arrange it in the morning to avoid bud withering and yellowing and to prolong the freshness of the flower heads.

(5) Broccoli is not suitable for long storage and should be eaten as soon as possible after harvest.