Choosing potting substrates for ornamentals and nursery stock

A professional potting substrate needs to suit the container as well as the crop. A mix that fills a small pot evenly may behave differently in a larger nursery container, where drainage, watering intervals and structure matter over a longer growing period.

Start with the peat fraction and the size of pot you use. Then check the pH, starter fertiliser and any added material against your own feeding and irrigation programme.

Match the fraction to the container

Medium peat fractions are a useful starting point for many ornamentals and nursery crops. They fill pots evenly while retaining a mix of smaller particles for water holding and larger particles for air. In practice, the right choice depends on the pot depth, the crop’s roots and how frequently you irrigate.

SOLVIKA’s 422W potting substrate uses white peat screened to 0-20 mm. For larger containers or crops held in pots longer, the 442W potting substrate uses a 0-40 mm white peat fraction. Both are pH-adjusted potting substrates with a wetting agent and a starter charge of 1.5 kg/m³ NPK 14:16:18.

A 0-40 mm screening is not a pot full of 40 mm pieces. It includes smaller material as well as coarser particles. Rather than choosing by the number alone, fill a few of your usual pots and check how the mix settles, wets and drains under your normal irrigation.

Think about structure across the growing season

Nursery stock may spend much of a season in the same container. During that time, repeated watering, handling and root growth can change how a substrate sits in the pot. A medium-coarse fraction can be useful where the aim is to retain air space as the crop develops, but fraction alone does not determine how long a mix will hold its structure.

Judge structure in the context of your system. Pot height, irrigation method, watering frequency and the length of time before sale all affect what you need from the mix. A shallow pot with a short crop cycle may call for a different balance from a deep container carrying a woody ornamental through a full season.

• At filling. Check that the mix runs through your filling equipment and leaves a consistent surface. Avoid pressing it harder in some pots than others, since compaction changes the space available for water and air.
• After watering. Compare pot weight and drainage across a representative batch. Look at the centre and base of the pot, not just the surface, before changing your irrigation schedule.
• Later in the crop. Lift a few plants and inspect the root zone. Note whether the mix has settled substantially or stays persistently wet at the base.

Treat starter fertiliser as the beginning of the feed plan

SOLVIKA’s professional potting substrates in the catalogue contain 1.5 kg/m³ NPK 14:16:18, a wetting agent and peat adjusted to pH 5.5 to 6.5. That starter charge provides an initial nutrient supply. It is not a substitute for a crop-specific fertiliser programme throughout the season.

How soon to start supplementary feeding depends on the crop, irrigation, container size and growing conditions. Frequent watering can move nutrients through a pot more quickly, while different ornamentals have different nutrient demands. Monitor the crop and root-zone EC and pH using the methods you normally rely on, then adjust feeding to your results.

If you prefer to set every nutrient addition yourself, SOLVIKA also offers pH-adjusted base substrates with a wetting agent and no fertiliser. Those are a different starting point from a ready-to-use potting substrate. Make that distinction clear when specifying a mix, particularly if your nursery applies its own fertiliser at the potting line.

Choose additions for a reason

A peat fraction is only one way to adjust how a substrate behaves. SOLVIKA’s potting range also includes versions with 10% perlite or 15% wood fibre. These options are worth trialling when you want to change the physical character of a familiar fraction or reduce the peat share, rather than assuming an addition will suit every crop.

For example, 422WP10 combines a 0-20 mm white peat fraction with 10% perlite. It has the same stated pH range and 1.5 kg/m³ NPK 14:16:18 starter charge as the plain professional potting examples above. Compare it in your own containers against the plain mix, keeping pot size and watering practice the same during the trial.

Wood fibre versions contain 15% wood fibre. When testing one, watch both irrigation response and feeding results as the crop grows. The useful question is not whether one ingredient is generally better, but whether the complete mix helps you manage that crop in that pot.

Run a small comparison before changing the nursery mix

Choose a representative crop and compare candidate substrates in the pots you actually use. Fill and water them in the normal way, then record how evenly they fill, how quickly they wet and drain, and whether the pots remain uniform across the bench. Keep the trial long enough to observe the root zone beyond establishment.

If your range includes both small ornamentals and larger nursery stock, you may find that one fraction does not serve every line equally well. Separate the decision by pot size and crop duration rather than forcing every crop into a single recipe. Compare any change in substrate alongside the irrigation and feeding adjustments it may require.

Write down the fraction, peat type, pH range, starter charge, additions and packaging you need when asking for a recommendation. SOLVIKA’s cited potting products are available in 50 L, 70 L and 250 L packaging. Naming the intended pot sizes and crop duration will help narrow the choice more than asking for a general-purpose mix.

Frequently asked questions

For a substrate recommendation or delivered price, send us your crop, pot sizes, current specification, required packaging, volume and destination. Include your preferred delivery term so we can assess the request.