How to Choose and Use Fertiliser for the Garden and Houseplants

In brief: Choose a fertiliser according to the ratio of nitrogen (N), phosphorus (P) and potassium (K) on the pack and according to what the plant needs at the moment – leaves, roots, or flowers and fruit. Apply liquid fertiliser every 7–14 days during the growing period; slow-release granulated fertiliser is enough once every 6–8 weeks. After the end of summer, stop nitrogen fertilisers so that woody plants and perennials can ripen before winter.

Liquid fertiliser	every 7–14 days during the growing period (spring to summer)
Slow-release granulated	once every 6–8 weeks
Last nitrogen feed	end of July to mid-August
Fertiliser registration in the Czech Republic	Act No. 156/1998 Coll., recorded by ÚKZÚZ
Categories according to ÚKZÚZ	fertilisers, auxiliary soil substances, biostimulants, substrates

Fertiliser on its own solves nothing. It helps only when it matches what the plant needs at that moment, and when you use it in a sensible dose and at the right time. More definitely does not mean better – an over-fertilised plant is usually worse off than one that received fewer nutrients.

In this overview you will find out what the abbreviations on a fertiliser pack mean, when to reach for a mineral and when for an organic fertiliser, how to time feeding in containers and in beds, and what to ask before you buy a fertiliser.

What NPK means and why it matters

The three numbers on the front of the pack (e.g. 7-3-6) give the percentage of nitrogen, phosphorus and potassium. Each of these nutrients does a different job in the plant, and a shortage of each shows up differently.

Nutrient	What it gives the plant	Sign of deficiency
Nitrogen (N)	growth of leaves and stems, deep green colour	pale green to yellow leaves, weak growth
Phosphorus (P)	root growth, setting of flowers	dark purple tinge on leaves, few flowers
Potassium (K)	resistance to drought and frost, fruit quality	browning leaf edges, soft fruit
Magnesium and calcium	chlorophyll formation, strength of cell walls	yellowing between the veins, deformed new leaves

A general-purpose fertiliser with a balanced NPK ratio, such as BIOPON universal, is suitable as a basic choice for most garden and indoor plants, unless you are growing something with markedly specific requirements.

Mineral or organic fertiliser

Mineral fertiliser contains nutrients in a precisely defined concentration, the plant takes them up quickly and the result is visible within days. Organic fertiliser (compost, manure, slurry, horn meal) releases nutrients more slowly, because soil microorganisms must first break it down – but in return it improves soil structure and also works as a store for months ahead.

In practice the two complement each other well: organic fertiliser in autumn or when preparing the bed, mineral or combined fertiliser during the season according to the plants' current needs. The topic is covered in more detail in the article Organic fertilisers – a complete guide for gardeners.

Liquid, granulated or sticks: how and when to use fertiliser

The form of the fertiliser determines how often you will apply it and how easy the dosing is.

Dilute liquid fertiliser according to the instructions on the pack and apply it with watering, usually every 7–14 days during the period of active growth.
Work slow-release granulated fertiliser into the substrate or soil; it lasts 6–8 weeks and is suitable for plants where you do not want to keep checking on feeding often.
Push fertiliser sticks into the substrate at the edge of the pot; they are suitable mainly for houseplants in smaller containers.
After application, water the plant with plain water if the instructions on the pack recommend it – you will prevent root burn from a high concentration of salts.

Feeding in containers and on the balcony

Plants in pots have nowhere to draw extra nutrients from, so they need feeding more regularly than those in a bed. For pelargoniums and other balcony flowers a liquid fertiliser such as BIOPON for pelargoniums is suitable, and for strawberries in containers AG Biomin strawberry fertiliser. Anyone who is just starting out and does not want to deal with several packs at once will appreciate the Biotabs Starterpack with a complete set of fertilisers for the whole season.

Fertiliser for more demanding plants

Some plants have special fertiliser requirements and a general-purpose product is not enough for them. Azaleas, rhododendrons and other acid-loving woody plants need a fertiliser for acidic substrates, otherwise their leaves gradually turn yellow even when there are enough nutrients – for example BIOPON for azaleas and rhododendrons can help. Orchids, in turn, need fertiliser at a lower concentration and with a different nutrient ratio than ordinary houseplants, which is what, for example, BOPON Elixír DUO for orchids is designed for. If you are looking for a granulated mineral fertiliser with even release for broader use in the bed, a suitable choice is Cererit Mineral universal granulated.

When to stop feeding and how to recognise over-fertilising

You can recognise over-fertilising by scorched leaf edges, a white coating of salt on the surface of the substrate or, conversely, by lush, soft growth that is prone to fungal diseases and frost. If this happens, stop feeding and flush the substrate thoroughly with a larger amount of water.

Stop nitrogen fertilisers for woody plants and perennials at the latest at the end of summer, so that the plant has time to ripen its wood before winter. In autumn, a fertiliser with lower nitrogen content and a higher proportion of potassium is suitable instead, such as BIOPON autumn universal.

What to ask before buying a fertiliser

Fertilisers, auxiliary soil substances, biostimulants and substrates placed on the Czech market are subject to registration with the Central Institute for Supervising and Testing in Agriculture (ÚKZÚZ) under Act No. 156/1998 Coll. The manufacturer must provide an analysis of the product and correct labelling on the label. ÚKZÚZ then carries out spot checks to see whether fertiliser in shops corresponds to what is stated on the pack.

When choosing, it therefore pays to look at the legible composition and dosage on the label, not just the marketing slogan. The difference between a substrate and a fertiliser, and when each is suitable, is described in the article Is it better to buy a substrate or a fertiliser?, and the current European rules in EU Fertilising Products Regulation (FPR) – what it means for gardeners.

Frequently asked questions

How can I tell that a plant needs extra feeding?

The most common signal is slowed growth, paler leaf colour or few flowers at a time when the plant should be flowering. If you water the substrate regularly and the plant still languishes, try a general-purpose fertiliser in a lower dose first.

Can mineral and organic fertiliser be combined?

Yes, they commonly complement each other. Organic fertiliser improves the soil and supplies nutrients in the long term, while mineral fertiliser helps quickly at the moment when the plant needs nutrients, for example before flowering.

How often should houseplants be fed in winter?

Most houseplants grow little or not at all in winter, so either skip feeding completely or limit it to a quarter dose once every 4–6 weeks.

Is fertiliser dangerous for pets?

Concentrated mineral and organic fertilisers can irritate the digestive tract of dogs and cats if swallowed. After application, store them out of their reach and follow the safety instructions on the pack.

Must every fertiliser be registered with ÚKZÚZ?

Fertilisers, auxiliary soil substances, biostimulants and substrates placed on the market in the Czech Republic are subject to registration. The only exceptions are certain minor cases defined by law, which an ordinary consumer practically never encounters in a shop.

Sources

Updated: 10 October 2026