Helle Terrakottatöpfe mit Geranien in verschiedenen Farben und Größen auf einer Holztreppe vor einer Holzwand

Everything you need to know about fertilising geraniums

Geraniums conjure up summer charm on balconies and terraces with a minimum of care. But even they cannot thrive on air and love alone. As so-called vigorous growers, they need a good dose of nutrients to grow and flower. And they get that by fertilising.

Geraniums are easy-care plants that, with the right fertiliser regime, will enhance your balcony for many months and bloom profusely with colourful flowers. 

Auf einer mit Teppich, Korbsessel und Beistelltisch wohnlich eingerichteten Terrasse gießt eine junge Frau eine prachtvolle Geranie im Topf.

Find out on this page:  

  • How to make geraniums bloom effortlessly with liquid fertiliser  
  • How often you should fertilise geraniums with liquid fertiliser  
  • Why it sometimes makes sense to use slow-release fertiliser  
  • When it’s time to start fertilising  
  • When you no longer need to fertilise  
  • Why balcony plants such as geraniums need fertiliser at all 

Fertilising geraniums at a glance

The most popular method for fertilising geraniums is to use liquid fertiliser. Dilute the concentrate with the water you use for watering at regular intervals.  


The advantage: Poured directly onto the soil, the roots of the plant absorb the nutrients immediately. Liquid fertiliser is particularly useful during the main growing season, when vigorous balcony plants need lots of nutrients to grow strongly and bloom profusely.  


For a nutrient boost that lasts longer, slow-release fertiliser is the best choice. Mixed into the soil, it provides your geraniums with all the nutrients they need to look their best for practically the whole season. 


Geraniums only need fertiliser during the growing season. This applies to upright, hanging, scented, butterfly, and interspecific geraniums as well as regal pelargoniums. The growing season in Europe is from about mid-May to early autumn.   

As soon as the days get shorter and the temperature drops, geraniums go into a dormant phase. Fertilisation can even harm the flowers because they can no longer convert the nutrients they are given. The tissue becomes soft, which makes these easy-care balcony plants susceptible to pests and diseases. 

Fertilising geraniums with liquid fertiliser - how does it work?

  1. Fill a watering can with water. 
  2. Measure out the right amount of fertiliser (use a dosing aid). 
  3. Pour the liquid geranium fertiliser into the water. 
  4. Stir the mixture with a stick. 
  5. Pour the solution directly onto the compost in the window box or planter. It’s best not to do this in direct midday sun. Make sure nothing gets on the leaves or flowers and nothing runs off.  


Depending on the product, mix liquid geranium fertiliser or flowering plant fertiliser into the water weekly or every 14 days, according to the dosage instructions.  

If the soil in the pot is so dry that it comes away from the edge, first moisten it with plain water and only then fertilise. This will not damage the roots. The fertiliser will also be better absorbed. 

Don't want to think about fertilising every Saturday or every other Saturday?

Then add a very small amount of liquid fertiliser to the water every time you water. Geraniums usually respond well to 1ml of liquid fertiliser per litre of water.   

A syringe or shot glass will help with dosing if the dosing aid provided isn’t suitable. Add 10ml of liquid fertiliser to a 10-litre watering can. That is 1cl, or half a shot glass. 

Liquid fertiliser works quickly and precisely

Roots only absorb nutrients dissolved in water.  

Just like the ones you give with liquid fertiliser!  

Maybe the sun is shining extra brightly this year and the geraniums are growing like crazy. Or it’s raining a lot and the rain is washing out nutrients. In both cases, liquid fertiliser meets your plants’ high nutrient requirements quickly and precisely.   

Jump to this section if you are interested in why it’s worth buying special liquid geranium fertiliser. 

Why are slow-release fertilisers often recommended for fertilising geraniums?

In slow-release fertilisers, better known as controlled-release fertilisers, a membrane encapsulates the nutrients. They are released gradually in small amounts. This is why slow-release fertilisers promise maximum flowering for months with minimum maintenance.  


How much of the controlled-release fertiliser’s nutrients are released in what time depends on the temperature and moisture in the soil – in other words, on the same factors as plant growth.   


If the plants need a lot, a lot is released. If they need less, they get less. Clever! We also recommend using slow-release fertiliser.  

Hände stecken Düngekegel in weißen Pflanzkasten mit pinken Geranien.

How often you need to fertilise your geraniums with it

With slow-release fertiliser, once mixed into the soil according to the dosage instructions when planting, you won’t have to think about feeding for several months.  


However, keep the following in mind: It’s not guaranteed that one application of slow-release fertiliser will last the whole season. Depending on the temperature and soil moisture, your geraniums may need an extra dose of plant food in late summer. This applies to plants in balcony boxes as well as geraniums in pots.  


If, despite slow-release fertiliser, flowering and growth decline, liquid fertiliser will help you out.  


If, at some point, you notice your geraniums are no longer flowering vigorously or their leaves are turning yellow, even though everything else is fine, start adding liquid fertiliser to the water regularly. This will feed your geraniums just as they need it – even in late summer.  


Fertiliser sticks work in a similar way to slow-release fertiliser pellets. You can insert them into the soil at any time after planting. The dosage depends on the size of the planter. 

Are there any other fertiliser products for geraniums?

These methods for fertilising geraniums have been tried and tested millions of times and proved their worth. Of course, there are also people who fertilise their geraniums with home remedies. Some even fertilise them with milk! We have written a separate article on this topic.   


Follow the link “Fertilising geraniums with home remedies” if you are interested.   


Or do you know people who use coffee grounds as fertiliser? We look at the pros and cons in the article “Fertilising geraniums with coffee grounds: Does it work?” to get to the bottom of it. 

When to start fertilising geraniums?

Start fertilising at the beginning/mid-June. After about four weeks, the fertiliser in the fresh potting compost you planted your geraniums in will be practically used up. 



Why not fertilise from the start?

Firstly, because the plant doesn’t initially need more nutrients than are in the soil. Additional fertiliser would be a waste of money. Secondly, the roots should still make an effort to obtain nutrients. The plants develop a more efficient root system as a result. This will often help them over the course of the summer. 


When to stop fertilising geraniums?

In Europe, fertilising is no longer worthwhile by the end of September at the latest. By then the days are shorter and the nights are cooler, so your geraniums will grow more slowly than in summer. They will manage with the remaining nutrients still in the soil. 

Nutrients have an influence on overwintering

If you plan to overwinter your geraniums, stopping fertiliser signals to the plants that it’s time to prepare for the dormant phase. Their metabolism slows down and the cells get ready for winter.  

Why geraniums need fertiliser

Geraniums are popular, flowering balcony plants. They grow by forming new cells. This is known as organic matter.  


Organic matter consists of chemical elements, the nutrients. The plant obtains these from the soil. If there aren’t enough nutrients available, we provide them by fertilising.  


The most important nutrients (known as key nutrients) are nitrogen (N), phosphorus (P) and potassium (K). Their content is listed on all fertilisers.  


All plants need nitrogen (N) for their metabolism and for the green pigment chlorophyll. If they have enough nitrogen, geraniums will be rich green and bursting with vigour. If there is a lack of nitrogen, their leaves will be pale green and they will not grow at all. Too much nitrogen makes plants susceptible to diseases. 


Phosphorus (P) promotes flowering. It is considered a power nutrient for the plant cells. If it is lacking, geraniums flower less and the leaves turn reddish in colour. Caution: Too much phosphorus will impair growth.  


Potassium (K) regulates the water balance. It strengthens a plant’s tissue, boosts its defences and is needed for fruit formation. You can recognise a potassium deficiency when the older leaves dry out from the edges first.  


Plants also need calcium (Ca), sulphur (S) and various trace elements such as iron (Fe) and magnesium (Mg).  


Special liquid fertilisers for geraniums or flowering plants contain all the necessary nutrients to promote abundant flowering and bright colours. Healthy growth is assured by using them. 

Why does it have to be flowering plant fertiliser?

Fertiliser for foliage plants is not suitable for feeding geraniums. It doesn’t contain phosphorus. Fertiliser for vegetable plants is usually low in potassium and therefore not ideal for geraniums.  


If you value sustainable gardening, buy natural geranium fertiliser made from organic raw materials from a garden centre. 

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