The optimal spraying time and fertilizer selection for cucumber leaf surface fertilizer in open fields

When growing cucumbers in the open field, if you want the plants to grow vigorously, produce more fruits and have good quality, foliar fertilizer is definitely an indispensable helper. Compared to fertilizing the roots, foliar fertilizer is absorbed faster and takes effect more quickly. It can quickly replenish nutrients for the cucumbers and solve problems such as nutrient deficiency, weak growth, and poor fruit setting. However, many farmers use foliar fertilizer, either they choose the wrong time or mix the fertilizers randomly, spending money but getting poor results. Today, using simple language, I will explain to you in detail about the foliar fertilizer for open-field cucumbers, when is the best time to spray it, which fertilizer to choose, and teach you step by step how to use the foliar fertilizer correctly to grow high-yield and good-quality cucumbers. 
Let's talk about the best time for spraying during the day. This is particularly crucial as it directly affects the fertilizer's effectiveness. When applying foliar fertilizer to open-field cucumbers, it is essential to avoid hot and strong sunlight, strong winds, and rainy days. The most suitable time is before 9 a.m. on a sunny day, or after 4 p.m. On cloudy days without strong sunlight, you can spray at any time of the day. Why these two periods? Before 9 a.m., the dew has just dried, the temperature is not high, the light is gentle, and the stomata of the cucumber leaves are fully open, allowing the fertilizer to be absorbed quickly; after 4 p.m., the sun is not as intense, the temperature is gradually decreasing, and the pesticide solution stays on the leaves for a longer time, allowing for full absorption, and it won't evaporate too quickly due to high temperatures, preventing the fertilizer concentration from rising and burning the leaves.

Remember this: Do not spray between 10 am and 3 pm. At this time, the temperature is high and the sunlight is strong. The pesticide solution dries out in just a few minutes. It cannot be absorbed and it is prone to burning the leaves. Spraying on windy days will cause the fertilizer to be blown away, resulting in waste and uneven distribution. Do not spray 1-2 hours before rain either, as the rain will wash away the fertilizer, wasting your efforts in vain. If it rains within 4 hours after spraying, wait until the leaves dry completely after the rain stops and then make sure to spray again to ensure the effectiveness. 
Let's talk about the entire growth period of cucumbers. At different stages, which foliar fertilizers should be applied? The requirements vary at each stage, and only by choosing the right fertilizer can it be effective. 
First, during the seedling stage, from the time the cucumber plants are transplanted until they start flowering, this period is mainly focused on nourishing the roots and strengthening the seedlings. The goal is to make the plants grow robustly, with lush green leaves, and to enhance their resilience. No excessive fertilization is necessary. Instead, focus on supplementing amino acid foliar fertilizers or seaweed fertilizers, as these types of fertilizers are gentle and contain small molecule nutrients that can be directly absorbed by the leaves. They can promote root growth, allowing the roots to penetrate deeper, and also enhance the cold resistance and disease resistance of the cucumber seedlings, preventing the occurrence of weak or yellow seedlings. Generally, one to two applications are sufficient during the seedling stage, with an interval of about 10 days. The concentration should be diluted according to the instructions and do not add more by yourself.

Then comes the flowering and fruiting period, which is the critical stage for the growth of cucumbers. Protecting flowers and fruits, and increasing the fruit setting rate are the core issues. If the nutrients are insufficient, problems such as flower drop, fruit abortion, and low fruit setting will occur. During this period, the preferred fertilizer is phosphoric acid potassium + boron fertilizer, which is regarded as a golden combination. Phosphoric acid potassium can replenish phosphorus and potassium elements, promoting flower bud differentiation and making the flowers bloom more vigorously; Boron fertilizer can promote pollen germination and increase the success rate of pollination, effectively reducing flower and fruit drop, and allowing more cucumbers to set fruit. Liquid boron and chelated boron fertilizers have better absorption effects. The spraying concentration should be controlled at 0.1%-0.2%, while the concentration of phosphoric acid potassium is 0.3%. Spray once before flowering and again during the flowering period, and the fruit setting rate can be significantly improved. 
Next comes the fruit expansion stage. After the cucumber fruit settles in place, the key is to rapidly expand and improve the quality of the fruit. During this stage, a large amount of potassium is needed, as well as calcium supplementation. Potassium fertilizer can be selected as high-potassium foliar fertilizer or 0.3% phosphoric acid potassium, which can promote the expansion of cucumber fruits, make the fruit stems straight and taste sweet, and also accelerate the ripening process. Calcium fertilizer can prevent cucumber cracking and bottom rot, enhance fruit hardness, make cucumbers more resistant to storage and less prone to rot, and has the highest efficiency in calcium absorption, without reacting with other fertilizers. During the fruit expansion stage, spray once every 7-10 days, and do this for 2-3 times continuously. As a result, the cucumbers will be larger in size, better in appearance, and the yield will also increase.

Finally, during the late stage of the result peak period, after continuous harvesting of cucumbers, the plants are prone to premature aging and yellowing of leaves. At this time, it is necessary to balance fertilization and prevention of premature aging. A mixture of 0.3% diammonium phosphate and 0.5% urea can be used. Urea can quickly replenish nitrogen, keeping the leaves green and preventing premature aging. Diammonium phosphate can continuously supply phosphorus and potassium, ensuring continuous cropping and more fruit production in the later stage. It can also be combined with multi-element compound micro-fertilizers to supplement iron, zinc, magnesium and other trace elements, preventing leaf yellowing and deformed fruits, and extending the harvest period. 
Apart from the timing and fertilizer selection, there are a few minor details to pay attention to when applying the spray. First, the application should be uniform. Focus on spraying the back of the cucumber leaves, as there are more stomata on the back side, which enables faster nutrient absorption. The front side should also be sprayed as well. Second, the concentration must strictly follow the instructions. It's better to be slightly diluted rather than concentrated, as too high a concentration can burn the leaves. Third, foliar fertilizers cannot replace root fertilization. They can only serve as an auxiliary measure and should be combined with root fertilization to ensure better growth of cucumbers. Fourth, foliar fertilizers can be mixed with insecticides and fungicides to save labor. However, a small-scale trial should be conducted first to avoid causing pesticide damage. 
Overall, for cucumber plants grown in the open field, applying foliar fertilizer in the morning and evening (the two prime time periods) can help promote strong seedlings during the seedling stage, protect fruits during the flowering stage, improve quality during the fruit expansion stage, and prevent premature aging in the later stage. By selecting the right fertilizer and applying it scientifically, the cucumber plants can grow robustly and continue to bear fruits, resulting in a double increase in yield and quality. Farmers who grow cucumbers, if they follow this method, will definitely have a good harvest.