How to tell the difference between depot fertiliser balls & snail or slug eggs in soil


I am a student of agricultural sciences and a real country kid. At home, I love tending my small vegetable garden and spending time out in nature. When not outdoors, I love to write. Beyond gardening and writing, however, I am particularly passionate about wildlife.

Favourite fruit: currants and raspberries
Favourite vegetables: salsify, savoy cabbage and potatoes

Snail eggs or just small stones? What are those little balls in the potting soil? Let us clear up the mystery.

Hand holding soil with fertiliser beads
The white beads are deposit fertilizer

Oh my goodness – you open a new package of potting soil and suddenly see those little yellow balls. But what are they? Surely not a home delivery of fresh snail eggs, which will soon become voracious vegetable destroyers? Do not worry, of course, it is not a delivery of pests. The small beads are fertiliser, which will not only not harm your plants but will even help them. After all, it provides the plants with nutrients for several months – without you even noticing.

Depot fertilisers: nutrients from nowhere?

Depot fertilisers provide our plants with nutrients over a long period of time. The small spheres are in fact nutrient salts that are coated with a synthetic resin. This shell first protects the nutrient salts from water so that they are not washed out within a few days. But how do the nutrient salts get to the plant in the first place? This secret also lies in the shell. This has countless small micropores through which water can penetrate the inside of the beads as steam. The nutrients inside are thereby dissolved. Gradually, the nutrient solution gets back out into the plant substrate via the permeable resin coating. However, due to the small size of the pores, it takes much longer for water to wash the nutrient salts out of the synthetic resin shell: this results in a uniform discharge of nutrients, meaning the plant is continuously supplied with nutrients over a longer period of time as if by magic – all you have to do is water it regularly.

Another advantage of many depot fertilisers is that the release of nutrients is dependent on temperature. Since the extent of plant growth is also temperature-dependent, it is convenient if the release of depot fertilisers also increases with rising temperatures. However, even this can have its limits: At some point, excessive heat gets to the plants. If the nutrient release of the depot fertilisers is purely temperature-dependent, this can lead to salinisation of the substrate and consequently to lasting plant damage. No one wants that, which is why there are depot fertilisers that do not overshoot the optimal range of nutrient release, especially at high temperatures, and thus preventively counteract plant damage.

Hand full of yellow fertiliser beads
Depot fertiliser beads come in various colors

But there are not only yellow-white grains: red, green or blue balls can be found in some potting soils. These beads are also depot fertilisers. But then why the bright colours? This is not about a fashionable appearance or a joke – the coloured sheath is intended as a guide for manufacturers and gardeners and reflects how long the depot effect of the fertiliser lasts. This is in fact extremely variable: the small balls can reliably supply your plants with nutrients between two months and over a year. Of course, the decisive factor is the standing time of the plants to be fertilised:

  • Potted plants with several years of standing: Use depot fertilisers with a long release period
  • Seasonal plants such as bedding and balcony plants: Mix depot fertiliser with a release period of about 4 to 5 months into the substrate.
Soil with depot fertiliser beads throughout
Different colors indicate various durations of action of the depot fertilizer

Test: snail eggs or depot fertiliser?

The soil may also harbour snail offspring, especially if the flowers have been outside in the pot for a long time. But how do I distinguish whether depot fertiliser or snail eggs are sharing space with my flowers? The test is child’s play: simply take the suspicious ball between two fingers and crush it. With a depot fertiliser ball, you will hear a cracking sound as the resin shell breaks. In addition, the ball feels dry even after crushing. Snail eggs, on the other hand, have no solid shell and accordingly make no sound. Furthermore, they feel slippery and moist between the fingers. Even if it is difficult to tell whether it is a friend or foe with the naked eye, a simple finger test will make it even clearer for the layperson. Furthermore, snail eggs are not usually found alone, but clumped together in groups. The depot fertiliser, on the other hand, should be distributed as evenly as possible in the substrate used, so it is more of a coincidence if two depot fertiliser pellets are found next to each other.

This is how you distinguish depot fertilisers from snail eggs:

  • Depot fertiliser beads are…
    • coated with a synthetic resin that characteristically cracks when crushed between the fingers.
    • usually found individually and well distributed throughout the substrate.
  • Snail eggs are…
    • not encased in a solid shell.
    • slippery and wet.
    • usually found in a clutch of several eggs.
Hand pinching fertiliser bead
If the bead cracks when crushed, it is depot fertilizer
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