Fertilizing and Humidity Conditions for Indoor Ferns


Plants in pots have only a limited amount of space for their roots to grow, along with relatively little compost at their disposal, so nutrients are used up relatively quickly. The possibility for plant nutrients to be supplied from deeper layers of soil or through the production of humus, as would be the case in the wild, is not an option for pot plants. For this reason, you must make sure there is an adequate substitute.

Suitable fertilizers for indoor ferns:

fronds of Microlepia unfurlingThe nutrients required by ferns can be divided up by quantity into main nutrients and trace elements. The main nutrients include nitrogen (N), phosphorus (P), potassium or potash (K), magnesium (Mg), calcium (Ca), and sulphur (S). Use a liquid multi-nutrient compound fertilizer for your indoor ferns, in which phosphorus and potassium occur in a balanced ratio. This information should be listed on the packaging in the form N + P + K ; for example, in the ratio 8 + 8 + 6. Ordinary liquid fertilizers, available in the trade, are also suitable. They usually contain the necessary trace elements of iron, manganese, copper, zinc, molybdenum and boron.

A simple and time-saving way of supplying nutrients is by the use of controlled-release fertilizers. These products release nutrients gradually into the compost and, over many weeks, ensure an even replenishment without the mineral salt concentration rising too much.

How to fertilize correctly:

Keep the dose for ferns very low, In the case of liquid fertilizers, half the amount recommended for green plants will be sufficient. The concentration to use is normally 0.05% which is the equivalent of 0.5 g fertilizer per litre of water. You may give liquid fertilizer in water when watering, add it to water used for immersing or even occasionally spray it on to the plants, For most ferns it is best to give a dose of fertilizer at fortnightly intervals. Some require more nutrients and therefore need a weekly dose of fertilizer; others manage on a dose every four weeks.

In their natural environment tropical ferns are not used to a clearly defined change of seasons nor to the alternation of growing and dormant periods during the year. In a temperate climatic region, however, they are practically forced to endure a rest period in the winter due to the decreased amount of light. For this reason, you should fertilize only in the spring and summer as, during the rest of the time, their nutrient requirement is not very high under ordinary indoor conditions.



Most ferns demand high humidity and will, therefore, be particularly comfortable in a greenhouse, an enclosed plant picture window, a glass case or a bottle garden. A warmish conservatory containing lots of other plants will also engender enough humidity for ferns. Things are a little more difficult in a room also lived in by humans. Dry air rising from a radiator on to a windowsill is like poison for most species of fern. The following suggestions will help to increase humidity.

• Do not stand the plants on their own but in groups. This will improve the mini-climate.

• Frequent misting of the plants. This is a lot of work, however. Furthermore, some species, such as Blechnum and Platycerium, do not like water lying on their leaves.

• Ensure indirect humidity by means of water evaporators on your radiators or with electric humidifiers. It is also helpful to stand the fern on top of an upside-down saucer in a dish filled with water. An alternative is to place the fern pot inside another pot lined with moist peat.

23. May 2011 by Dave Pinkney
Categories: House Plants, Indoor Ferns | Tags: | Comments Off on Fertilizing and Humidity Conditions for Indoor Ferns


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