Geranium care: maintenance & diseases
The flowers of geraniums are stunning. Here is our guide to geranium care from the right way to prune, water, fertilise and avoid diseases.
Pelargonium (also known as geranium) belongs to the family Geraniaceae. Most of the approximately 250 wild species are native to South Africa, but were introduced to Europe in the 16th century. They were mistakenly classified in the genus Geranium. However, Pelargonium and Geranium differ in their flower structure. Due to this taxonomic faux pas, Pelargonium was initially falsely classified as Geranium. However, since then the geranium has achieved immense popularity and is now available in an array of hues. New colour variants are being created through intensive breeding. From May to the first frost in autumn, the flowers of the numerous varieties shine in all the colours of the spectrum from white to red to violet. But it is not only its appearance that makes it one of the most popular bedding and balcony plants. Compared to other plants, they are also less susceptible to diseases and pests, can be reproduced and overwintered very easily. For all these reasons, you can see the colourful variety of their flowers on almost every balcony during summer. The following guide will provide you with all the information about geranium care, so that your balcony can be embellished with these wonderful plants too.
Geraniums are not high maintenance. But in order for their beautiful flowers to appear in large numbers on strong shoots, your geranium needs a lot of fuel in the form of water and regular fertilisation. The use of scissors supports healthy growth and is strongly recommended before putting these South African beauties to overwinter. In this article you will learn everything about watering, fertilising, cutting back and hibernating geraniums so that you can keep your balcony friends in wonderful shape.
Watering geraniums correctly
Geraniums need a lot of water. Although they can completely dry out without sustaining any damage, they bloom especially abundantly if you water them regularly with lukewarm rainwater. However, make sure that their soil is not constantly wet. Therefore, it is better to water the plants once and thoroughly rather than more often with small amounts of water. Do not water again until the soil has dried out and avoid stagnant moisture.
Summary of watering geraniums:
- Water regularly and abundantly with lukewarm water
- Let the soil dry before watering again to avoid waterlogging
Tip: If your geraniums look limp and wilted despite sufficient watering, this may be due to root damage caused by waterlogging.
Geraniums are plants that require a lot of nutrients. Especially if potted, fertilising is unavoidable. You should fertilise these hungry plants from planting until October. You can use the following fertilisers for geraniums:
- Compost and horn shavings
- Fertilisers for flowers
- Mineral fertilisers such as blue grain
When planting, you can use a slow-release fertiliser such as compost and horn shavings. As a rule, three litres of compost per square metre and a handful of horn shavings should be worked into the soil. After that you do not need to fertilise for three to four weeks. Instead of compost or horn shavings, you can also work a mainly organic long-term fertiliser into the soil.
When choosing a fertiliser, you should make sure that the nitrogen content (recognisable by the ‘N’ of the NPK ratio) should be greater, whereas the phosphate content (P) should be the smallest. We recommend using organic fertilisers. This not only protects the environment, it also supports the microorganisms in the soil, because the nutrients are present in complex form and must first be broken down. This means that organic fertilisers also have a natural long-term effect. They can be used just once in spring with an occasional slight re-fertilisation afterwards. Mineral fertilisers, on the other hand, are given every one to two weeks in watering water. You can read here how to exactly fertilise the geraniums where you will also find valuable information about the nutrient needs of this plant.
Summary of fertilising geraniums:
- When planting, use slow-release fertilisers such as compost, horn shavings or organic fertilisers
- Occasionally re-fertilise; use mineral fertilisers every one to two weeks while watering
- Our recommendation: use mainly organic fertilisers with a high nitrogen and low phosphate content
Pruning geraniums correctly
Geraniums are generally very tolerant to pruning. For example, upright standing geraniums (or zonal geraniums) can be pruned in many different ways: you can shape the plant according to your desire and give free rein to your creativity. Those who like it low-maintenance can make do with cutting off the tips of the new shoots from spring to early summer. In this way, the geraniums will not overgrow. The cut-offs of the new shoots are ideal for growing cuttings and the mother plant is encouraged to branch out. How this works is explained in the following.
In rainy weeks there is an increased risk of rot or mildew on withered flowers. To avoid this, you should regularly remove (deadhead) the faded inflorescences by hand. This additionally strengthens the formation of new flowers, because by removing the flowers the seed formation is suppressed and new flowers are produced. It is recommended to do this weekly. With certain subspecies of ivy-leaved geraniums (Pelargonium peltatum), deadheading is not necessary because the plants lose their flowers themselves. Especially popular are the varieties ‘Cascade’ or ‘Villetta’.
For the last time during the season, the geraniums are cut back in September/early October before being moved to their winter quarters. The long, non-wooden shoots are shortened to about ten centimetres, leaving two to three knots per shoot. In addition, all leaves should be removed. After the geraniums overwinter, spring pruning takes place at the beginning of sprouting (around the beginning of February). Since geraniums bloom on new shoots, radical pruning leads to a particularly large number of flowering shoots.
Summary of geranium pruning:
- In summer: occasionally shorten shoot tips for a better growth
- Weekly: deadhead the geranium to minimize the risk of mould and rot
- Beginning of February and in September/October: prune thoroughly
Tip: If you trim one or more main shoots when cutting back trailing geraniums and only cut back the side shoots in spring, they will grow as climbers.
Geraniums unfortunately do not tolerate the temperate climate winter conditions and cannot survive winters outside unless in their sunny African homeland. In order for you to enjoy your geraniums for years to come, they have to be taken to their sheltered winter quarters before the first frost. This is ideally a dark and cool room, such as a cellar. Take the following steps and leave your geraniums in these conditions until spring:
- Carefully dig out the geranium
- Gently knock the soil from the roots
- Cut back as mentioned above
- Cover the roots with sand and potting soil in a pot or a bag
- Place the geranium in their winter quarters
The root ball should be watered regularly so that they do not dry out completely. During the hibernation period, fertilising is not needed.
Find out more about alternative hibernation strategies and other useful information to get your colourful companions through the winter here.
An overview of the most common geranium diseases
Geraniums are abundantly flowering plants if they are properly planted and cared for. The following pests or diseases can nevertheless occur.
Especially with wet leaves the susceptibility to geranium rust is increased. You can recognize a geranium rust infestation by the fact that the leaves turn yellow to brownish and pustules may appear on the underside of the leaves. Spots or rings are visible on the upper side of the leaves and spread quickly. Since geranium rust is contagious, you should remove and dispose of affected leaves as quickly as possible in the event of initial infestation. In addition, you can support the plant with a plant fortifier and should absolutely avoid watering the plant from above. The geranium should also be protected from rain.
The so-called botrytis (also called grey mould) is a common fungal disease. Similar to geranium rust, it is more likely to occur in cold and wet conditions. If your geranium shows rotten spots with a grey spore coating, it is most likely diseased. Then you should first remove the infected parts and keep the plant dry. Spraying with organic active agents with straw and oats can also help strengthen the plant.
Aphids also often target geraniums. An aphid infestation frequently occurs in winter when the plant is in the dark and grows only a little. The aphids suck on the leaves and, as a result, the leaves become wavy, which makes the infestation recognizable. If this is the first infestation by aphids, rinse the geranium thoroughly with water. If it occurs more frequently, you can also control the aphids with soapy water.
While grey mould and geranium rust usually occur during wet weather, geraniums can be attacked by spider mites during dry weather. The infestation is distinguishable by silver dots on the upper side of the leaf and webs on the underside. In most cases it is sufficient to spray the geranium with water and treat it with a plant strengthening agent.
Greenhouse white flies
Especially in wind-protected, warm locations and in winter, geraniums are susceptible to infestation by greenhouse white flies. The pests settle on the underside of the leaves and cause yellow spots on the leaves by puncturing the plant skin when feeding. Affected leaves then dry out and fall off. To treat a less severe outbreak, you should remove affected leaves and attach sticky yellow panels to capture the flies. Wasps are natural predators of the white flies. To combat white flies naturally, wasps could be a solution.
Summary of the most common geranium diseases:
- Geranium rust turns the leaves yellow to brownish; pustules sometimes appear on the underside of the leaves; spots or rings are visible on the top of the leaves and spread quickly; contagious
- When geraniums have grey mould or botrytis, rotting spots with a grey spore coating occur
- An infestation by aphids can be recognized by the undulating leaves
- Spider mites leave silvery dots on the upper side of the leaf and silk-like webs on the lower side
- White flies settle on the underside of the leaves and cause yellow spots on the leaves by feeding; the affected leaves dry out and fall off
- Find out what to do if geraniums have yellow leaves in this article.