Fertilising potatoes: when, how & what to feed potato plants

Potatoes are highly versatile and popular, as well as being highly nutritious. Find out all you need to know about fertilising potatoes for a bountiful harvest.

The potato (Solanum tuberosum) is a member of the nightshade family (Solanaceae). It originated in South America and was brought to Europe by seafarers about 400 years ago. Since then, the tuberous vegetable has been an important food staple that is grown in many home gardens. However, for adequate growth and a plentiful harvest, the nutrient-rich potato plant must be optimally supplied with nutrients.

When is the best time to fertilise potatoes? Which fertilisers are suitable and is there a proper way to fertilise? Here is a summary of the most important information about fertilising potatoes.

When to fertilise potatoes?

Firstly, potatoes are not grown from seed, but rather from seed potatoes or healthy potatoes that have not yet germinated. Each “mother potato” sprouts offshoots, which in turn can form up to 12 new tubers. Due to its high nutrient requirements, this tuberous vegetable is ideal as a first crop in the garden year. The first fertilisation is best done when planting in spring.

Tip: In addition to fertilising, find out what other potato care measures should be taken in our specialised article.

There are two main potato varieties, early or ‘new’ potatoes and maincrop. Early potatoes grow relatively quickly, can be harvested as early as June and are ready to be eaten right away. If the soil has warmed up enough, the pre-sprouted tubers can be planted and fertilised as early as the beginning of April. On the other hand, planting and fertilising maincrop varieties for an autumn harvest does not begin until the end of April to the beginning of May. Then, after two months at the most, fertilise the potatoes again to provide them with optimal nutrients. To protect other plants, soil and animals in the garden, it is best to use quality natural slow-release fertiliser. The optimal amount of fertiliser can vary depending on the product − always follow the manufacturer’s instructions.

Pro tip: To give the young potato plants the best possible start, work some manure or compost into the soil in autumn before planting in spring.

Potato fertiliser: what to feed your potato plants

A bountiful harvest is only possible if the potatoes are fertilised properly. However, overfertilising or unbalanced fertilising is also undesirable and can lead to an increased susceptibility to potato diseases. Here are our tips for optimal fertilisation of potato plants.

Fertilising potatoes naturally

Using natural slow-release fertilisers in your garden makes sense from both a scientific and a sustainability point of view. These are primarily made up of organic material, which is gradually broken down by the organisms that live in the soil. The nutrients resulting from this process are then made available to the plants. Meanwhile, the soil structure is also improved in a sustainable manner. Compared to using chemical fertilisers, natural slow-release fertilisers are particularly gentle on the environment.

Not only is our Plantura Tomato Food a plant-based, slow-release fertiliser, but it is also environmentally friendly and easy to use. Because the fertiliser’s composition is based on the nutrient requirements of high-yielding vegetables, it is also ideal for fertilising potatoes. Its granular form ensures that the essential nutrients are available to your plant in a natural manner, both immediately and over time.

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Here are our detailed instructions to help ensure that your plants are supplied with the right amount of nutrients.

Natural slow-release fertiliser: Instructions and dosage amounts for potatoes

• Before planting: work 100 − 180 g/m² of our Plantura Tomato Food into the upper soil layers.
• After planting, water well so that the granules can dissolve.
• After 2 months, fertilise again with 80 − 120 g (7 to 10 heaped dessertspoons) per plant.

Fertilising potatoes with minerals: blue grain, calcium cyanamide, etc.

Mineral fertilisers are easily soluble and can be absorbed by the plant directly. However, the amount of fertiliser used should be carefully calculated in relation to the nutrient requirements of the potato plant. With mineral fertilisers, this can prove to be difficult and, in turn, increase the risk of overfertilisation and nutrient leaching. Furthermore, fertiliser salts are harmful to soil life because they decrease the number of nitrogen-fixing bacteria and create a hostile environment for earth worms.

Lime fertiliser for potatoes is also controversial. According to experts, such fertiliser promotes plant diseases. Advocates, on the other hand, highlight benefits such as increased quality and yields. Lime raises the pH of the soil and the ammonium in the fertiliser provides nitrogen to the plant over a long period of time. Calcium cyanamide should be handled and applied with caution and, above all, plenty of time before planting (at least three weeks ahead of planting). However, the high price of Calcium cyanamide is generally out of proportion to its effect.

Fertilising potatoes with home remedies

Tried and tested home remedies and natural fertilisers from your garden can also be used to nourish your potatoes. When planting, spread some compost over the tubers before covering them with soil. You can also work compost or manure into the soil the autumn before planting the potatoes. As the compost decomposes over the winter, the nutrients are available to the plants in spring. During the flowering period, you can also make your own plant liquid manure. Nettle manure is high in nitrogen and, when combined with a potassium-rich comfrey liquid fertiliser, it becomes an effective plant pick-me-up. To use a liquid manure, dilute it with water in a 1:10 ratio, and water the plants with it once a week in the morning or evening.

Pro tip: The benefits of liquid manure can be enhanced further by mulching with nettle and comfrey leaves.

At a glance: how to fertilise potatoes

• Apply the first fertilisation ahead of planting the potatoes by working compost or slow-release fertiliser into the soil.
• Slow-release fertilisers − such as our Plantura Tomato Food − promote soil life and provide long-term nutrients to the potato plant.
• Mineral fertilisers promise quick results but carry the risk of overfertilisation and damaged soil life.
• Natural fertilisers (compost, manure, plant liquid manure) provide potato plants with additional nutrients.

Green manuring and crop rotation

To improve the soil conditions, sow green manure in autumn before planting potatoes the following year. Legumes, such as peas (Pisum), clover (Trifolium) and vetches (Vicia), are particularly suitable as green manure. They use their roots to draw nutrients (especially nitrogen) up from deeper soil layers while also loosening the soil. As these plants are not frost-hardy, they die over the winter and can be worked into the soil in spring. Because potatoes have high nutrient requirements, it is recommended that they are grown on a at least four-year rotation plan to give the soil plenty of time to replenish nutrients between cultivations.

After harvesting early potatoes, you can already use the bed to plant other vegetables over the summer. Various types of cabbage (Brassica), for example, are suitable secondary crops. Crop rotation avoids one-sided nutrient removal from the soil and prevents the spread of pests, such as the Colorado potato beetle (Leptinotarsa decemlineata).

Pro tip: Potatoes also thrive particularly well in mixed cropping. For example, you can sow spinach between the rows, harvest it later and leave the remains as mulch. This reduces weeding and the roots can remain in the soil to later become humus.

Learn everything about potato companion plants in our special article.