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Beautiful and healthy indoor plants delight every hobby gardener. Fresh green in the living room is good for the soul and has a calming effect. To ensure that you can enjoy your houseplants, it is essential to fertilize them regularly.

Why do you need to fertilize indoor plants?

Regular fertilizing is essential for indoor plants because the soil in the pot only provides limited nutrients. During its growth, the plant consumes the nutrients available from fresh substrate or fertilization. However, these are used up more or less quickly. Now the plant needs replenishment in good time if it is not to starve - because if the necessary nutrients are missing, the plant will no longer grow and eventually die.

How long indoor plants can survive without fertilization depends on the plant species, their species-specific nutrient requirements and their growth rate. Basically, slow-growing plant species such as cacti have a low nutrient requirement and can therefore do without an additional nutrient supply for a long time. Some plants even thrive without any additional fertilizer, as long as they are repotted annually in fresh (and therefore nutrient-rich) substrate. Other green plants, on the other hand, grow very quickly and have a correspondingly large appetite. Many popular indoor plants, such as the various Ficus or Dracaena species, the Dieffenbachia or the green lily, need a basic supply of important nutrients every seven to 14 days between March and October.

Necessary nutrients

In order for green plants to grow and thrive healthily, they need different nutrients in the right composition. The main nutrients - these are the ones that are indispensable for every plant - are called:

  • Nitrogen (abbreviated N, for nitrogenium)
  • Phosphorus (P)
  • Potassium (K)
  • Magnesium (Mg)

A so-called NPK fertilizer contains all the important nutrients and is therefore suitable for the regular fertilization of indoor plants.

NKP is a compound fertilizer

The individual components fulfill different functions in the plant metabolism: Nitrogen allows the plant to grow and ensures growth of shoots and leaves. In addition, nitrogen is indispensable for leaf green formation - if you value beautiful houseplants with strong green leaves, you must ensure a balanced nitrogen fertilization. But be careful with the dosage, because excess nitrogen makes the tissue soft and susceptible to diseases and pest infestation.

Phosphorus is necessary for the formation of roots and buds as well as for fruit and seed ripening. Green plants generally need a little less of this than flowering plants, as they rarely develop flowers and fruits. Potassium makes plant tissue strong and resistant to diseases and pests, and the substance is also important for photosynthesis. Magnesium is also essential for green plants, because plants need it primarily for the development of leafy green.

Don't forget trace elements

But the main nutrients alone are not enough. Trace elements are those nutrients that plants also need to live - even if only in very small doses. For the smooth flow of life processes, plants need

  • iron
  • copper
  • manganese
  • molybdenum
  • zinc
  • and boron.

All four main nutrients as well as the vital trace elements must be contained in a commercially available complete fertilizer. These are dosed differently depending on the plant's needs.

How do you fertilize indoor plants?

There are a variety of fertilizers you can use to feed your plants. The simplest solution is to use a ready-made product from a specialist retailer. This has various advantages, for example

  • an optimal nutrient composition
  • matched to green plants
  • a guaranteed amount of nutrients
  • optimal dosage recommendations

On the other hand, these fertilizers are often synthetically produced or mineral compositions, which in turn are problematic for ecological reasons - for example, because the nutrient cycle is not maintained or the raw materials used in production cause environmental damage. If you avoid such problems and value biologically safe fertilization, use natural-based products or make them yourself. Some of the remedies available in every household are also suitable for the nutrient supply of your green plants.

mineral fertilizers

Bromeliads are poured directly into the leaf funnel.

Mineral fertilizers are available in different compositions and forms. Liquid fertilizers that you add to the irrigation water are particularly user-friendly. Fertilizer sticks that you just stick into the substrate are also very easy to use. The disadvantage of mineral fertilizers, however, is the high proportion of nutrient salts, which quickly leads to over-fertilization in salt-sensitive green plants - for example many types of succulents. This in turn results in increased susceptibility to (fungal) diseases and pests. On the other hand, if you use organic fertilizers, you are less likely to overdose.

Tip: The correct dosage of mineral fertilizers depends on the salt sensitivity of the plant roots. Two milliliters (or grams) of fertilizer per liter of water is sufficient for most green plants. Be sure to follow the manufacturer's dosing instructions, use dosing aids and, if in doubt, make a solution too weak rather than too strong. Salt-sensitive indoor plants such as orchids and ferns should be given a particularly low dose of fertilizer.

Fertilize organically, of course

Plant fertilization is natural and organic when you use organic-based fertilizers. These have various advantages:

  • slow decomposition of the substances
  • gradual release of nutrients to the plant
  • therefore low risk of over-fertilization
  • and continuous nutrient supply
  • long-term care
  • No chemicals, therefore gentler on people and the environment

For indoor plants, we recommend special products from specialist retailers based on organic raw materials such as compost or stable manure. Use these according to the manufacturer's recommendation. Basically, these fertilizers belong to the long-term fertilizers, so you only have to supply your green plants with them once or twice a year. Organic long-term fertilizers supply the plants with all the necessary nutrients for much longer than commercially available mineral fertilizers.

Appropriate home remedies

Basically, you don't even need to buy the fertilizer, but use organic waste from your household. Particularly suitable for fertilizing green plants

  • coffee grounds
  • tea bag (black tea)
  • eggshells
  • Wood ash (blessed is he who has a chimney)
  • and banana peels.

Are you one of those people who don't really wake up in the morning without their coffee? Then don't throw away the daily coffee grounds! It contains the most important nutrients (especially the main nutrients nitrogen, phosphorus and potassium) and is ideal for fertilizing indoor plants. Dry the coffee base, roughly spread it out on a baking tray, because it molds quickly when it is wet. But be careful: coffee is not suitable for long-term fertilization because it lowers the pH value of the substrate.

You can counteract this by giving crushed egg shells, for example, because these contain lime and other minerals that are valuable for plant growth. Caution with lime-sensitive green plants: These should never be fertilized with egg shells! On the other hand, cooled wood ash, which contains a lot of potassium and provides various trace elements, can be used more universally. Only use this agent if you have burned pure, untreated wood without any additives. By the way, wood ash is also a good antidote to fungal and rotting diseases in plants.

Disadvantages of home remedies

You should think twice about using home remedies, because they involve certain risks. The main disadvantages of coffee grounds, wood ash and the like are:

  • do not contain all the nutrients in the necessary amounts
  • Nutrient composition is unknown
  • therefore no exact dosage possible
  • Overdose or underdose likely
  • Malnutrition of green plants
  • Occurrence of deficiency symptoms
  • increased susceptibility to disease and pest infestation

Tip: Compost is a wonderful fertilizer that you don't even need a yard to make. With the help of a so-called worm box - a special composting container - you can even convert organic kitchen waste into fertile compost in your kitchen or on the balcony.

When and how often to fertilize?

The rule of thumb for the frequency of fertilizing says: During the growing season, houseplants should be fertilized every two weeks. However, distinguish between fast-growing and slow-growing species. Fast-growing plants have a higher nutrient requirement and should therefore be fertilized weekly, while slow-growing plants should only be fed every four weeks. If you use long-term fertilizers (e.g. in the form of fertilizer sticks), fertilizing two to three times a year is sufficient, depending on the manufacturer's information. The first application of fertilizer takes place in March, the second in summer between June and July. Since most plants take a break in the winter months between October and March, they are not fertilized during this time. Exception: plants without a rest period.

Fertilize according to the lunar calendar

The moon has serious effects on our life on earth, as confirmed above all by the readers living on the North Sea coast. Experienced indoor plant gardeners ascribe the different phases of the moon not only to an influence on the tides, but also on the effect of fertilizer application. If you want to fertilize according to the lunar calendar, always apply the fertilizer when the moon is waning - if possible on the days immediately after the full moon. At this point in time, nutrients should be able to penetrate the soil more quickly and develop their full effect. When the moon is waning, you can therefore dose the amount of fertilizer less.

Golden fertilizer rules

Even if you now know when, how often and what is the best way to care for your green plants, you can still cause serious damage through incorrect fertilization. So that this doesn't happen to you, we have formulated these golden fertilizer rules for you:

  • Never apply fertilizer to the dry root ball.
  • Never fertilize in full sun.
  • It is better to administer the fertilizer more often and in low doses than infrequently and in high doses.
  • Only fertilize when the plant is growing.
  • If the plant gets little light (e.g. in a dark location or in winter), then it needs less fertilizer.
  • If there is a lack of light, the nutrients are not utilized and, in the case of mineral fertilizers, the substrate becomes salty.
  • Stop fertilizing in case of pest infestation and diseases.
  • Only continue with the nutrient supply after successful control.
  • In no case does fertilization replace regular repotting.

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Indoor plants