When should cucumbers be fertilized, and what type of fertilizer works best?

　　Cucumber, also known as huqua or qinggua, belongs to the genus Cucumis in the family Cucurbitaceae and is one of the major greenhouse crops. Cucumbers have high water requirements and strong water‑absorbing capacity; therefore, they should be grown in soils with good water‑retention properties and require regular fertilization.

　　So when do cucumbers need fertilizing, and what kind of fertilizer works best? Let’s find out below.

　　I. When Should Cucumbers Be Fertilized?

　　1. Fertilization for Cucumbers – Germination Stage

　　From sowing until the emergence of the first true leaf is the germination stage, which typically lasts 5 to 6 days. During this period, relatively high temperature and humidity are required to promote early and uniform emergence and to enhance seedling survival. Nutrient demand is low at this stage; it is generally sufficient to apply a well‑balanced base fertilizer, which is usually composed primarily of organic matter.

　　2. Fertilization of Cucumbers – Seedling Stage

　　From the emergence of 4–5 true leaves until transplanting, this stage is known as the seedling period and typically lasts more than 30 days. It is a critical phase for floral bud differentiation and for establishing early yield potential. The primary tasks during this period are to promote floral bud differentiation and root development, with an emphasis on field management—appropriately controlling irrigation to encourage compact growth and ensuring adequate ventilation to harden off the seedlings.

　　3. Fertilization of Cucumbers – Early Flowering Stage

　　From transplanting to the opening of the first flower marks the initial flowering stage, which typically lasts about 25 days. During this period, vegetative and reproductive growth occur simultaneously. Begin supplemental fertilization, prioritizing slow-release organic fertilizers. Key management practices include increasing leaf area and the number of female flowers while preventing excessive vegetative growth.

　　4. Fertilization of Cucumbers – Fruit-Setting Stage

　　From the setting of the first fruit to the end of the growing season, this is the fruit‑setting period, during which the demand for various nutrients reaches its peak and represents a critical phase for yield formation. During this time, management should focus on ensuring adequate water and fertilizer supply.

　　During the early fruit‑setting stage, plant growth and fruit set are just beginning, so water and fertilizer requirements are low; simply keep the soil surface from drying out. In the second stage, as temperatures rise during the development of the middle‑size fruits, both water and nutrient needs steadily increase. This is also a critical period for yield formation, so heavy topdressing and frequent irrigation are essential—apply every 1–2 days. Finally, during the late fruit‑bearing stage, the plants enter senescence, and their demand for water and nutrients declines. Nevertheless, continued careful management of fertilization and watering is necessary to prevent premature decline of stems and leaves, extend the fruiting period, and boost overall yield.

　　II. What Fertilizer Works Best for Cucumber Cultivation?

　　1. Fertilization for cucumbers: increase the application of organic fertilizers.

　　Organic fertilizers not only supply cucumbers with the nutrients necessary for growth and development, but also reduce soil bulk density, increase soil porosity, and improve the soil’s physical and chemical properties. Therefore, organic fertilizers play a crucial role in maintaining high and sustained yields of cucumbers and in enhancing soil quality.

　　2. Fertilization of cucumbers: apply chemical fertilizers appropriately.

　　Cucumber roots are shallow and relatively fragile; excessive fertilizer concentration can lead to root burn. When applying chemical fertilizers, it’s best to feed the plants frequently in small doses. For base application, apply 25–30 kg of diammonium phosphate and 23–27 kg of potassium sulfate per mu. Throughout the growing period, supplemental fertilization is essential, with a total of 47–53 kg of urea and 52–58 kg of potassium sulfate per mu. In the early stages, focus on growth regulation; in the later stages, combine fertilization with irrigation and harvesting, applying nitrogen and potassium fertilizers every 7–10 days (or using a liquid fertilizer containing equivalent nutrient levels).

　　3. Fertilize cucumbers and apply foliar fertilizer.

　　Foliar fertilization is typically applied during the peak fruit‑setting stage, when nutrient supplies are relatively abundant in the early growth phase. After fruit set, reproductive growth intensifies and nutrient demand increases significantly. Moreover, at this stage, lower temperatures reduce root activity and diminish the plant’s capacity to absorb nutrients. To meet the nutritional requirements for normal fruit development, foliar application of fertilizer can help replenish the nutrients needed by the plants.

　　4. Use bio-organic fertilizer for cucumber fertilization.

　　Increasing the application of organic fertilizers and bio‑fertilizers while appropriately reducing chemical fertilizers is an essential strategy for producing pollution‑free, green food. In newly constructed greenhouses, a single application of 8 kilograms of high‑quality bio‑organic fertilizer can promote vigorous cucumber growth, enhance fruit set, produce longer, more uniform fruits, and extend the harvest period.