Narcos ProMix 50 Liter

A 50 litre bag of potting soil built on sieved sphagnum peat, blended with perlite and lime, and lightly pre-fertilised. RHP certified, meaning its composition and properties are checked by an independent inspection body rather than simply declared by the supplier.

Lightly pre-fertilised, and that is the point

The label declares a starter charge of 0.4 kg per cubic metre of a 17-10-14-4 fertiliser. Scale that to this bag and you get roughly 20 grams in 50 litres. That is very little, and it is deliberately very little.

A heavily charged soil takes over the first weeks of your schedule. You feed, the soil feeds too, and your EC climbs without your knowing which part came from you. At this level a young plant has enough to establish itself and nothing more, so you start your own schedule on day one and measure what you actually gave. Narcos recommend Comp 1 with the stimulators from the same range alongside it.

Air is the figure that matters

Roots need oxygen, and in a pot the space that stays air-filled after watering decides how much they get. ProMix reaches an air content of 14 to 22 percent at a suction of 10 centimetres. That comes from two directions: the peat is sieved for structure, and perlite is blended through it, which takes up no water itself and holds the pores open.

Organic matter sits above 85 percent and moisture below 80 percent. The second figure is why a 50 litre bag weighs only 16 kilos: you are buying volume, not water.

Two pH values, two EC values, and why they differ

The label carries two pairs of values and they look like a contradiction. Measured on a 1:1.5 water extract, pH is 6.3 and EC is 0.5 mS/cm. Measured to the European standards EN 13037 and EN 13038, pH is 6.7 and EC is 19 mS/m.

Both are correct. They are two different extraction methods, and a different ratio of soil to water produces a different number by definition. So they cannot be read side by side, and if you compare this soil with another one, compare figures measured the same way. If you measure yourself, a 1:1.5 sample puts you on the first line.

Technical Specifications:

• Type: RHP certified peat mix, lightly pre-fertilised
• Volume: 50 litres (EN 12580)
• Weight: 16 kg
• Composition: black peat moss, blonde peat moss, perlite, lime
• Starter charge: NPK 17-10-14-4 at 0.4 kg per cubic metre
• pH (1:1.5 water): 6.3, tolerance 0.5
• EC (1:1.5 water): 0.5 mS/cm, tolerance 0.3
• pH (EN 13037): 6.7, tolerance 0.5
• EC (EN 13038): 19 mS/m, tolerance 11
• Organic matter: above 85%
• Moisture content: below 80%
• Air content at 10 cm: 14 to 22%

Frequently asked questions

Do I need to start feeding straight away?
You can begin your schedule from planting. The starter charge is there to help a young plant establish, not to carry it through the first weeks.

How many pots does a bag fill?
Fifty litres is four eleven-litre pots, or nine pots of five and a half litres. Expect slightly fewer than the arithmetic suggests, because soil settles once you press and water it in.

Can I blend in extra perlite or clay pebbles?
Narcos advise using this product as supplied. Perlite is already blended through it, and adding more changes both the structure and the starter charge per litre.

What does RHP actually certify?
RHP is the Dutch inspection scheme for horticultural growing media. A certified mix is checked for things like consistent composition and freedom from weed seed and pathogens, by a body that does not sell the product itself.