Fertilization
Even a well-prepared substrate provides nutrients to the plant for only 4–6 weeks. At different growth stages, tomatoes need different substances – it's worth considering this when planning fertilization.
Needs by growth stage
Intense growth begins after transplanting – in the first month, the need for phosphorus increases, ensuring a good root system and strong flowers. Darkening leaves with a purple tint indicate a phosphorus deficiency.
When flowers begin to form, the need for calcium increases sharply, peaking during flowering. Calcium determines the fruit's firmness, color, and taste, and increases resistance to fungal diseases. Drying leaf bases and blackening fruit tips signal a calcium deficiency.
Nitrogen demand increases when flowers start to set, but most fertilizers provide enough. Excess nitrogen promotes green mass growth, reduces the number of flowers, and increases nitrate accumulation.
Source: pomidorai.eu