de fertometer is een handige tool

General tips for plants in pots.

What is important for potted plants?

If we don't consider the flowers - which for plant lovers are of course the most important thing - we could say that a plant consists of three main parts: the roots, the stems and the leaves.
The roots take nutrients (minerals) out of the soil which are transported through the stems. These nutrients are necessary for production of amino acids, the building bricks of protein, and from these, chlorophyll (leaf-green) is formed. The leaves, in their turn, are responsible for photosynthesis - a process by which plants use sunlight to absorb CO2 and transform it into sugar. In this process oxygen is released and the plant 'breaths'.

The structure of the soil, the degree of acidity and the amount of nutrients play an important role in the growth of a plant, so the potting soil is of the utmost importance.

1. The structure of the soil has to be airy, well drained and consist of organic materials. Often garden peat, compost and/or coco waste is used. The presence of clay is important as it retains water in the soil. It is recommended to use good, professional potting soil.

2. The optimum degree of acidity - the pH-value (pondus Hydrogenii) - lies for most potted plants between 5,0 and 6,5 pH. If the pH is lower (3,5-5,0 pH) we speak of sour soil.

3. It is important to know if there are enough nutrients available at any moment - the amount of soil is limited and the nutrients quickly consumed.

Potting soil and feeding

If we consider a plant which is standing in good potting soil and where the structure of the soil and the pH-value are correct, we still do not know if enough nutrients are available in the pot. Perhaps the plant has enough fertiliser or manure to last for 6 weeks, or even 6 months, or it might not have been 'fed' at all for a long time.

Because of the limited amount of soil in a pot the proper fertilisation is much more delicate than with plants in open soil where the roots can reach several meters and will be able to absorb nutrients most of the time. For plants in pots we ought to know at any time what the situation is so we can fertilise if necessary. With the Fertometer you can determine this instantly!

Fertilising can be done with different products: organic manure, fertiliser granules or liquid fertiliser.
Do not be tempted to add more fertiliser than is allowed (see instructions on the package). For potted plants with lots of flowers we advise a well balanced NPK-proportion: 10-5-15 (NPK = Nitrogen, Phosphorus, Potassium).

A plant without a nutrient stock will, after fertilising, immediately consume everything and shortly a nutrient deficiency will exist again. However, building up a reserve supply of nutrients can take weeks and has to be done according to the instructions of the fertiliser producer. Do not be tempted to over fertilise. By measuring regularly you can prevent this. But if you feel that building up a nutrient reserve is taking too long, simply repot in a larger container for faster results.

When you add too much fertiliser, your plant will grow faster in the beginning, produce longer stalks and bigger leaves and will generally grow well. The disadvantage though is that the plant not only becomes weaker but will also produce large amounts of sugar, which will attract vermin such as lice. Tip: do you have ants on your plant? Then the lice are not far!


Be careful that the root ball does not get 'rooted'! When a root ball consists of only roots, there is no soil available and the plant gets rapidly exhausted. In that case you should put your plant into a bigger container (dead roots can be cut off).

Dense Soil

As a result of a too dense soil, roots cannot get sufficient oxygen. The plant will not be able to absorb enough nutrients and it is therefore better to repot it in a larger container.

Salinity of potting soil

Often plants stand in the same pot for years and look worse and worse. Fertilising has no effect; On the contrary, black points form on leaf ends as a result of over fertilising. In severe cases feed consumption is even blocked. Leaves will become yellow and fall off and a white crust forms at the rim of the pot. This is due to the salt content of the soil. When you water plants with water that has a high degree of salt, salinisation of the soil will happen quickly. The only remedy is to take the plant out of the pot, rinse it very well and put it in fresh compost with long life fertiliser. If necessary cut the plant back.


Water is essential for the growth of plants, for the transport of nutrients and for the 'cooling' of the leaves. We advise you to mix rainwater with tap- or groundwater.

OUnder normal conditions you can use rainwater because it is fairly clean and has a pH-value of 5,6. However in regions with lots of cars and industry the pH value can drop to a level between 3 and 4. This is too acidic and not suitable for watering potted plants.

Tap water as well as groundwater contains a lot of minerals (including calcium and magnesium) and oligo elements which are indispensable for plants. The pH is often much higher then for rainwater - around 8 - 8,5 (calciferous) and is too high for potted plants.

If only tap water is used, it is possible that a white crust will form at the rim of the pot similar to salinisation. This white residue can also appear on the leaves.

By mixing rainwater with tap- or groundwater, the ideal pH-value of 5,5 - 6,2 will be achieved more easily.