When to Fertilize Watermelons? A Detailed Guide to Timing and Methods
SummarySeedling stage fertilization: Before planting watermelons, apply sufficient basal fertilizer; no fertilizer is needed during the seedling stage. When the plants grow 3-4 true leaves, urea can be applied, taking care to keep it about 10-20cm away from the roots to prevent root burn. Vine extension stage: When the vines grow to 40-50cm, per mu you can apply urea, high-nitrogen compound fertilizer or potassium sulfate along with watering. Fruit swelling stage: The fertilizer demand is large, mainly phosphorus and potassium fertilizers. Late growth stage: If premature aging or yellowing and withering of the vines occurs, spray potassium dihydrogen phosphate.
I. Applying basal fertilizer
1. Before planting watermelons, sufficient basal fertilizer should be applied, mainly organic fertilizer, together with a small amount of chemical fertilizer; the basal fertilizer accounts for about 70% of the total fertilizer application.
2. If watermelons are planted in soil with medium or higher fertility, per mu you can apply about 4000 kg of organic fertilizer, together with about 15 kg of diammonium phosphate, about 25 kg of potassium sulfate, and about 15 kg of urea, then plow to mix the fertilizer evenly with the soil.
II. Applying topdressing
Watermelons can be fertilized according to the principle of light application at the seedling stage, timely application at the vine extension stage, and heavy application at the fruit swelling stage.
1. Fertilization at the seedling stage
During the seedling stage, if the basal fertilizer is sufficient, topdressing is basically unnecessary. Specifically, fertilization can be carried out according to the plant growth and soil fertility. Generally, topdressing can be done when the plants grow 3-4 true leaves, and per mu you can apply about 10 kg of urea. Note that it should not be too close to the roots; apply it at a distance of about 10-20cm to prevent root burn.
2. Vine extension stage
(1) The fertilizer amount can be appropriately increased according to the growth of the watermelons. When the vines grow to 40-50 cm, in order to promote faster vine growth, per mu you can apply about 15-20 kg of urea, about 20-25 kg of high-nitrogen compound fertilizer, or about 10-15 kg of potassium sulfate, which can be done together with watering.
(2) If sufficient basal fertilizer and seedling-promoting fertilizer have been applied to the plants, less nitrogen chemical fertilizer should be applied. During the vine extension stage, in order to avoid excessive growth of the watermelons and its effect on fruit setting, fertilizer should be applied earlier; in the middle and late vine extension stage, topdressing is basically unnecessary.
3. Fruit swelling stage
(1) During the fruit swelling stage, the fertilizer demand of watermelons is relatively large, so fertilizer must be applied in time, mainly phosphorus and potassium fertilizers, together with a small amount of nitrogen fertilizer, which helps promote fruit expansion and thus increases watermelon yield. The fertilization amount at this stage accounts for 50% of the topdressing amount, and can generally be applied in 2 applications.
(2) About 4-5 days after the plants finish flowering, when the fruits grow to the size of an egg, per mu you can apply about 5 kg of urea, about 25 kg of potassium sulfate, and about 15 kg of diammonium phosphate. About half a month after flowering, when the fruits grow to the size of a bowl mouth, use the hole application method, and per mu you can apply about 10-15 kg of potassium sulfate and about 15-20 kg of diammonium phosphate, then water at the end.
4. Late growth stage
In the late growth stage of watermelons, if premature aging or yellowing and withering of the vines occurs in the plants, in order to replenish plant nutrients in time, you can choose 0.2-0.3% potassium dihydrogen phosphate or 0.3-0.4% Feilibao for foliar spraying.