Fertiliser (NPK) Calculator
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Fertilizer calculator
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Other tools you may find usefulFertilizing plants and lawns - how to provide nutrients in appropriate doses
Proper fertilization is one of the most important care procedures in agriculture, gardening and taking care of home greenery. For proper growth, flowering and fruiting, plants need constant access to macro- and microelements. The three basic nutrients necessary for every plant are nitrogen (N), phosphorus (P) and potassium (K) - hence the name of mineral fertilizers: **NPK fertilizers**. The key to success is to administer these elements in appropriate doses and proportions. Both deficiency and excess of fertilizers are harmful. Overfertilization of plants (especially with nitrogen) may lead to soil salinization, "burning" roots, weakening frost resistance and susceptibility to diseases.
Our interactive fertilizer calculator makes it easy to precisely calculate the amount of mineral or organic fertilizer needed for a specific area of your garden or lawn, preventing dosage errors and saving money.
Three pillars of fertilization - the role of nitrogen, phosphorus and potassium (NPK)
Each letter on the fertilizer packaging means a specific element and is responsible for other life processes of the plant:
- Nitrogen (N):Responsible for vegetative growth, the structure of green mass (leaves and stems) and intense green color (synthesis chlorophyll). It is crucial in spring.
- Phosphorus (P):Supports the development of the root system, accelerates flowering and supports the setting of fruits and seeds.
- Potassium (K):Responsible for the plant's water management (drought resistance), regulates the uptake of other nutrients and strengthens resistance to frost and fungal diseases.
Table: Demand for NPK ingredients and dosage for popular crops
The table below shows the optimal NPK proportions and the average annual demand for the pure ingredient per 100 m² (1 are) of cultivated area:
| Crop / Plant | Recommended N:P:K ratio | Average dose of fertilizer per 100 m² (kg) | Best application date |
|---|---|---|---|
| Intensive lawn | 12 : 5 : 8 (spring) | 3.0 – 4.0 kg | Spring and early summer (after mowing). |
| Autumn lawn | 0 : 8 : 20 (without nitrogen) | 2.5 – 3.0 kg | September – October (preparation for winter). |
| Tomatoes and vegetables | 8 : 10 : 18 | 4.0 – 5.0 kg | Before planting (mixing with the soil) and top dressing. |
| Conifers | 10 : 10 : 20 | 2.0 – 3.0 kg | Spring and mid-summer. |
| Roses and ornamental shrubs | 12 : 12 : 12 | 3.0 kg | Spring (after pruning) and June. |
How to calculate fertilizer dose based on percentage?
Fertilizers are rarely 100% pure. The percentage composition is given on the packaging (e.g. NPK 15-10-20 fertilizer contains 15% nitrogen, 10% phosphorus and 20% potassium). If your plant needs 1 kg of pure nitrogen, you must calculate the dose of physical fertilizer according to the formula:
Fertilizer dose = Demand for pure ingredient / Percentage · 100
For example: 1 kg / 15 · 100 = 6.6 kg of NPK 15-10-20 fertilizer to provide exactly 1 kg of nitrogen.
Frequently asked questions (FAQ)
What does the NPK abbreviation on the fertilizer packaging mean?
The abbreviation NPK stands for three main macroelements necessary for plants: N - nitrogen (Nitrogen), P - phosphorus (Phosphorus), K - potassium (Kalium). The numbers next to the abbreviation (e.g. 10-20-10) indicate the percentage of these elements in the fertilizer.
What are the symptoms of overfertilization of plants?
Symptoms include: browning and drying of the leaf edges (so-called salt burn), limp shoots, unnaturally dark green color of the leaves in the absence of flowering (excess nitrogen) and white residue on the soil surface.
What is the difference between mineral and organic fertilizers?
Mineral (artificial) fertilizers are highly concentrated and act quickly, but they may salt the soil. Organic fertilizers (manure, compost, biohumus) work slower, but they improve the soil structure, enrich humus and are safe for the environment.
Why should you not use nitrogen fertilizers in autumn?
Nitrogen stimulates the plant to grow and sprout new green shoots. If applied in autumn, it will prevent the shoots from becoming lignified before winter, which will lead to freezing and destruction of the plant during frosts.
How to properly spread fertilizer on the lawn?
It is best to spread the fertilizer using a wheel seeder (crosswise - along and across the lawn), which guarantees even distribution. Spreading by hand often results in dark green stripes or burned patches of grass. After fertilizing, the lawn should be watered abundantly.