Chemical or natural fertilisers: a complete guide to feeding your plants without exhausting the soil
Chemical or natural fertilisers: what do your plants really need?
You look at your monstera and something bothers you. The new leaf is slow to unfurl, its green seems less deep and its once-conquering growth has dozed off. On a garden-centre shelf, two worlds face you. On one side, bottles of mineral fertiliser promise fast, measurable action. On the other, compost, plant extracts and organic fertilisers speak of living soil, slowness and balance.
Which to choose? Should you wake the plant up with an immediately available ration, or patiently feed the soil it lives in? The answer lies less in the opposition between "chemical" and "natural" than in a much simpler question: what does the plant need, right now?
Because fertiliser is neither a universal medicine nor a magic potion. It is more like a larder. The plant still has to be hungry, its roots have to be able to eat, and you have to offer it the right foods in the right proportions.
What do the three numbers on the bottle mean?
Almost every pack shows a mysterious formula: NPK 5-3-6, 10-10-10 or sometimes 4-6-8. These numbers are the condensed language of plant nutrition.
N stands for nitrogen, the great builder of leaves and young stems. When enough is available, the plant develops generous foliage. In excess, however, it can produce overly soft tissue, unbalanced growth and greater vulnerability to certain pests.
P, for phosphorus, plays a part in energy transfer, root growth and reproduction. K, or potassium, helps regulate water, keeps cells working and contributes to the plant's general resilience. Around this trio orbit magnesium, calcium, sulphur and a constellation of trace elements — iron, boron, manganese, zinc or molybdenum — needed in tiny amounts but sometimes decisive.
A yellowing leaf is therefore not automatically asking for fertiliser. It may lack light, suffer from too much water, be suffocating in a compacted mix or be unable to absorb iron because the pH is wrong. Adding nutrients in that case is like piling more food on a plate in front of someone who cannot eat.
Why does mineral fertiliser work so fast?
Mineral fertiliser provides nutrients in forms that roots can take up directly or quickly. In a pot, where the volume of compost is limited and regularly leached by watering, this precision can be valuable. A plant in full growth receives a known, repeatable dose that is easy to adjust.
That is the real talent of mineral fertiliser: it works with the precision of a measuring instrument. A plant grown in a poor mix, a heavily used container or an intensive vegetable plot can respond quickly to a well-calculated feed. But this speed has a darker side.
When the nutrient solution is too concentrated, the build-up of salts disrupts water exchange around the roots. Their fragile tips can be damaged as if they had touched an invisible ember. The symptoms are sometimes misleading: dried-out leaf edges, stalled growth, yellowing foliage and a whitish crust on the surface of the compost. Thinking they are seeing a deficiency, the gardener adds more fertiliser and makes the problem worse.
In this situation, it is better to stop feeding and let plenty of water run through the compost, provided the pot drains properly. The plant will then need time, suitable light and sensible watering, not another feed.
Is natural always gentler?
Compost seems to arrive in the garden with its hands full of promises. It does not just deliver nutrients: it also adds organic matter, improves soil structure and feeds a host of organisms that gradually turn that matter into elements plants can absorb.
Its action is less spectacular but deeper. Where soluble fertiliser feeds the plant directly, compost starts by feeding the soil. Bacteria, fungi and the small creatures underground become the garden's invisible cooks.
That does not mean every natural product is automatically harmless. Fresh manure can release a lot of nitrogen, contain unwanted organisms and burn young roots. Ground horn, very rich in slow-release nitrogen, can be overdosed. Fermented plant teas are also concentrated and must be used in moderation. As for wood ash, often presented as a free fertiliser, it is alkaline and rich in mineral salts: spread carelessly, it can upset the pH and supply too much potassium.
The word natural therefore never excuses you from observing, measuring and understanding.
What happens when nutrients leave the garden?
Whatever the roots do not absorb does not disappear. Some of the nitrogen can move as nitrate into groundwater, while nitrogen and phosphorus carried into rivers, lakes or the sea can encourage eutrophication. The water becomes covered with excessive plant growth and algae; as they decompose, they use up the oxygen that fish and aquatic organisms depend on.
The European Environment Agency points out that imbalances linked to nitrogen and phosphorus remain a major cause of the degradation of European ecosystems. Between 2016 and 2019, almost 36% of river monitoring stations in the European Union showed signs of eutrophication. (eea.europa.eu)
This pollution is not caused by mineral fertilisers alone. Too much manure or slurry can produce the same result. For water, a nitrate from organic matter is still a nitrate. The problem arises mainly when inputs exceed what crops need, are applied at the wrong time or land on soil that is bare, frozen, waterlogged or unable to hold them.
In Europe, the Nitrates Directive regulates, among other things, the spreading of livestock manure in vulnerable zones. The general benchmark remains a limit of 170 kg of nitrogen per hectare per year from livestock manure, with rules on when and how it may be applied. A targeted amendment adopted on 9 February 2026, however, provides additional, strictly conditional options for certain processed fertilising materials derived from manure, known as RENURE. (environment.ec.europa.eu)
So, do you have to pick a side?
In a living garden, the fairest choice rarely looks like a war of religions. Compost can form the foundation of fertility, while a carefully dosed mineral or organo-mineral fertiliser corrects a specific need from time to time. This alliance is often more sensible than the systematic use of a single product.
In the vegetable garden, start by looking at the soil. Is it dark, crumbly and full of worms, or pale, compact and almost lifeless? A soil test becomes particularly useful before adding phosphorus or changing the pH. In many gardens, fertilising blindly leads to a build-up of certain elements rather than correcting a real deficiency.
A soil low in organic matter will first need mature compost, properly decomposed plant residues, mulch and, where space allows, green manures. Legumes, together with nitrogen-fixing bacteria, can contribute to the fertility of a rotation, but they do not instantly drop a sack of nitrogen on the plot: a large share becomes available only after their tissues have been dug in and decomposed.
For tomatoes, squashes or container-grown plants, which are very hungry while growing, an extra feed can then be worthwhile. The secret is to split the feeds rather than pour in one large dose.
And indoors, where the soil fits in a pot?
A houseplant lives in a tiny world. Its roots explore a few litres of compost, sometimes less, and cannot go looking for a more fertile patch. Yet the light available indoors often limits how fast it grows. The weaker the light, the less the plant can use the nutrients it is given.
In spring and summer, when a plant is actually producing new leaves, a diluted liquid fertiliser can be applied following the label, starting cautiously at a reduced strength. In winter, many plants under natural light slow down considerably; continuing to feed them at the same rate then increases the risk of salt build-up.
The monstera appreciates balanced feeding while it is growing, but does not want to be drowned in nitrogen. The snake plant, slow and frugal, makes do with little. Orchids grown in bark need a very dilute fertiliser given regularly during active growth: composted bark alone is not a complete feed. As for calatheas, their sensitive foliage quickly shows that hard water or an overly concentrated fertiliser does not suit them.
Here again, the right frequency is not set by the calendar but by visible growth, light, temperature, pot size and how rich the compost was to begin with.
Do pets change the rules?
If a dog or cat roams the garden, read the label as you would read a medicine's. Even a fertiliser presented as organic can be dangerous if it contains attractive animal materials, such as dried blood, bone meal or certain by-products that may be eaten in quantity.
A common confusion also needs clearing up: glyphosate is a herbicide, not a normal component of mineral fertilisers. Some commercial products combine weedkilling and feeding, but these must then be regarded as specific formulations, not simple fertilisers.
After application, close the packs carefully, store them out of reach and keep the animal away from the area for as long as the label requires. In case of ingestion, do not make it vomit on your own initiative. Keep the product packaging and contact a vet or an animal poison centre immediately.
Is the Biobizz Try Pack a good starting point?
If you are looking for an organic approach for a few potted plants, the Biobizz Try Pack Indoor can be a practical way in. The official box contains three 250 ml bottles: Bio·Grow, Bio·Bloom and Top·Max. The manufacturer presents it as a basic feeding programme for around one to four plants. (biobizz.com)
Bio·Grow mainly supports the growth phase, Bio·Bloom is formulated for flowering and Top·Max is marketed as a flowering stimulant. The small format lets you try the range without immediately buying large containers. On the other hand, it will soon run out if you look after many pots or very hungry plants.
This pack should not, however, be seen as an automatic solution. The right dose depends on the growing medium, water quality, the species grown and light intensity. It is better to consult the official feeding chart, then start modestly rather than aiming straight for the maximum dose. Claims about taste, yield or final quality also depend on many factors and should not be taken as guarantees.
How do you know when to stop?
Successful feeding leaves few visible traces. The plant grows steadily, its internodes stay in keeping with the light it receives and its leaves keep a normal colour. It neither turns soft under an avalanche of nitrogen nor freezes under a crust of salts.
A plant recently repotted in enriched compost generally does not need fertiliser straight away. A plant that is sick, dehydrated, infested with pests or deprived of light must first get back suitable growing conditions. Feeding a suffocating root does not cure it any more than a big meal cures someone who is short of air.
The safest rule fits in a few words: a small dose at the right time is better than a big dose given out of worry.
Feeding the plant without starving tomorrow
Natural or mineral fertiliser? If you were waiting for an outright winner, the garden answers with a riddle. Mineral fertiliser acts quickly and precisely, but demands great discipline. Organic matter works more slowly, improves the soil and supports its biological life, without being risk-free when badly prepared or overdosed.
In the garden, first build soil fertility with mature compost, plant cover and suitable rotations. In pots, choose a formula that matches the plant and its growing medium, then dilute with care. In every case, observe before you act.
Because the plant is not asking you to choose between chemistry and nature. It is only asking you to understand its language: a leaf that pales, a root that struggles to breathe, growth that surges or stops. Once you learn to hear these signs, fertiliser stops being a recipe. It becomes a measured gesture, almost a conversation between you, the plant and the living soil that works in silence.
Sources and references
European regulation of fertilising products is governed in particular by EU Regulation 2019/1009, which sets requirements for composition, labelling and limits on certain contaminants, including cadmium in several product categories. (eur-lex.europa.eu)
Information on nutrient pollution, eutrophication and the pressures exerted by nitrogen and phosphorus comes from publications and indicators of the European Environment Agency. (eea.europa.eu)
The features and contents of the Biobizz Try Pack Indoor were checked against the manufacturer's official documentation, consulted on 8 September 2026. (biobizz.com)