Feeding cucumber plants: when, how & what fertiliser?


With a passion for growing installed at an early age, I have always been happiest outdoors in nature. After training as a professional gardener and horticultural therapist, I currently run horticultural therapy and community kitchen gardens in the UK, helping others access the many physical and mental health benefits of growing vegetables, fruit and plants.

Favourite fruit: apples and pears
Favourite vegetable: asparagus

For the tastiest fruits and healthy robust plants, it is well worth regularly applying fertiliser to your cucumber plants. Read on to find out which fertilisers are right for cucumber plants and how often to apply them.

Cucumbers growing on a plant
For an impressive harvest, cucumbers require the correct nutrients [Photo: Leo Pakhomov/Shutterstock.com]

Cucumbers (Cucumis sativus) are a popular fruit to grow and rightly so, as they are easy to care for and nothing quite beats the refreshing taste of a cool and crisp homegrown cucumber. Cucumbers not only need fertile soil to grow well, but they also need to be fertilised regularly to ensure healthy, strong plants with plenty of good-sized fruits.

Do cucumbers need fertiliser?

If you are wondering whether your cucumber plants need fertiliser, the short answer is yes. Cucumbers are hungry feeders and can crop for weeks on end, using up precious energy to produce flowers and the subsequent fruits. If you do not provide an ongoing supply of nutrients, especially for those grown in containers, the plants may stop cropping earlier and struggle, leading to decreased resistance to stress and disease.

cucumber plant being fertilised
Slow-release granular fertiliser can be used to feed cucumber plants [Photo: FotoDuets/ Shutterstock.com]

When should you feed cucumbers?

If you are unsure when to start feeding cucumber plants, it might be later than you think.

When sowing cucumbers, they do not need any extra nutrients because their seeds already contain everything that is needed for germination. This is why it is best to use a seed sowing compost that is low in nutrients, like our Plantura Organic Herb & Seedling Compost. Too many nutrients can actually harm or kill off your seedlings.

Cucumber plants need a boost of nutrients for the first time when they are potted on or planted out into a greenhouse trench or grow bag. They are ready for this when they are around 15cm tall with several true pairs of leaves. Plant the cucumber seedlings into a good quality potting soil, like our Plantura Organic Tomato & Vegetable Compost. It is ideal, as it contains all the nutrients the young plants need for their first 4 to 6 weeks, when they concentrate on putting on a lot of new growth.

Organic Tomato & Vegetable Compost, 40L
Organic Tomato & Vegetable Compost, 40L
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  • Perfect for tomatoes & other vegetables such as chillies, courgettes & more
  • For strong & healthy plant growth as well as an abundant vegetable harvest
  • Peat-free & organic soil: CO2-saving composition

It is at this point or soon after that the cucumber plants put on a huge amount of growth and will benefit from a slow-release fertiliser with a high level of nitrogen.

However, as soon as the first flowers start to appear the cucumber plant requires a higher level of potassium to encourage further flowering and subsequent fruiting. A high potassium fertiliser, such as tomato feed or a balanced fertiliser mix including potassium can be used as per the instructions.

cucumber being watered by can
Liquid fertilisers are easy to apply [Photo: nieriss/ Shutterstock.com]

Best fertiliser for cucumbers

Cucumbers require different levels of nutrients at their different stages of growth, using more nitrogen whilst they are growing strongly and more potassium when flowering and setting fruit.

Cucumber plant food can either be applied in the form of slow-release granules or liquid that can be applied at the same time as watering. Caution: cucumbers are quite sensitive to an increased salt concentration at their roots, which builds up when using higher doses of soluble mineral fertilisers. It is better to use organic fertilisers that have a slower and more balanced nutrient release as well as additional organic substance to feed soil microorganisms than mineral fertilisers.

Liquid feeds are fast acting compared to granular fertilisers and need to be applied every 1 to 2 weeks. Our organic Plantura Liquid Tomato Food is simple to mix and can be applied when watering your plants, making it easy to administer. With a blend of both nitrogen and potassium, it is ideal for healthy growth and plentiful fruits.

Liquid Tomato Food, 800ml
Liquid Tomato Food, 800ml
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  • Perfect for tomatoes & other vegetables
  • Liquid fertiliser for healthy plant growth & an abundant harvest
  • Quick & easy application - child & pet friendly

For those who prefer to apply fertiliser less frequently, our granulated organic Plantura Tomato food feeds your plants for up to 3 months at a time, making it only necessary to apply twice during the growing season; apply the first dose when planting.

Using nettle (Urtica dioica) and comfrey (Symphytum officinale) to make homemade fertilisers is another way of providing your cucumber plants with the nutrients they need.

Nettle tea or nettle soup as it is also known, is made by mixing chopped-up nettles with water; let it steep or brew for 2 to 4 weeks. Dilute with water at a ratio of 1:10 to 1:20 and water the cucumbers with the nettle tea. Nettle fertiliser is a completely natural liquid feed that is full of micronutrients, iron, and nitrogen, making it perfect to feed cucumber plants with whilst they are actively growing.

Once made, comfrey tea contains many nutrients, especially potassium, making it ideal for feeding cucumbers when they are actively flowering and fruiting. Make it in the same way as nettle tea. Comfrey tea is also quite strong and concentrated and needs diluting with water at a ratio of 1:10.

Making nettle fertiliser for cucumbers
Homemade nettle fertiliser can be used to feed cucumbers [Photo:Foxxy63/ Shutterstock.com]

Both homemade fertilisers can be applied every 1 to 2 weeks at the relevant growth stage.

Tip: remember to wear gloves when collecting the foliage because nettles sting and comfrey’s hairs can irritate the skin.

When it comes to the best fertilisers for cucumbers grown in pots or containers, it is often easiest to use a liquid feed. Not only is liquid feed faster acting, but it is also easy to apply and there is less chance of overdosing a small pot. Plus, it can be difficult to work granular feed into a container tightly packed with roots. That said, if you are growing cucumbers directly in soil, such as in a bed, it can prove easier and quicker to use a granular feed, which needs fewer applications and can be worked into the soil more freely.

Feeding cucumbers: step-by-step

If you are wondering how to feed cucumber plants for the first time, do not worry; we will walk you through how to fertilise your cucumbers, whether you are using a liquid feed or granular feed.

Stirring liquid fertiliser
Liquid feeds need to be thoroughly mixed before applying [Photo: Galina Sharapova/ Shutterstock.com]

Applying a liquid feed to pots and beds

  • If the soil is dry, pre-water the soil so that it is moist but not wet. This will ensure an even uptake of the fertiliser and prevent the liquid feed from draining straight through the pot and soil.
  • Following the fertiliser’s dosage instructions, measure the liquid feed and add to the water in a watering can and mix thoroughly. Rainwater is ideal.
  • Apply to the soil around the plant, avoiding the foliage.
  • Repeat every 1-2 weeks or as instructed.

Applying a granular feed to beds

  • Before planting, add the recommended amount to the planting area and work into the soil.
  • Water thoroughly to help break down the granules and release their nutrients into the soil.
  • Apply a second dose after 2-3 months or as instructed.
  • Spread the recommended dose evenly around the base of the plant, leaving an area of roughly 10cm around the stem clear.
  • Carefully work the granules into the soil, being careful not to damage any roots.
  • Water in to activate the nutrient release.

Our slow release granular Plantura Tomato Food is ideal for feeding cucumber plants and as it is plant-based, it is almost impossible to over-fertilise your plants with it.

Tomato Food, 1.5kg
Tomato Food, 1.5kg
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  • Perfect for tomatoes, chillies, courgettes, cucumber & more
  • For healthy plants & an abundant tomato harvest
  • Long-lasting fertiliser that is free from animal products - child & pet friendly

Feeding cucumber plants will help maintain plant health and encourage fruiting throughout the growing season, hopefully resulting in a bumper crop. Find out how to harvest and store your cucumbers in our expert article.