@Time It is the amount of the same fert used that makes it last longer. The canadian type isn't sold in the us at all the us version has only a starter amount if you look on there site. It is not really a hot soil there is a guy that even adds nutes at seedling stage on youtube that has great success with it although I wouldn't add any the first few weeks, a lot cheaper than coco and some say it even holds water better coco is better cause no nutes but this stuff is like 14 bucks for 2 cubic ft and is available at any lowes or menards it's more of a convienience and price thing is why I suggested.
Also you don't want to use the 9 month pre fert soils they will burn your plants up in seedling stage if you want something water only look into super soils Mephisto will sell you the stuff to mix in to make supersoil if you email them or there are a lot of recipes online.
I did look on their site. https://www.promixgardening.com/en/product/detail/promix-premium-potting-mix
The Premium potting soil, both the US and Canadian version, have 9 month ferts listed in addition to the mycoactive stuff. The only difference is the Canadian version uses coco and the US version uses polymer gel.
- With MYCOACTIVE technology to stimulate vigorous growth for greater stress resistance, larger root system for increased nutrients, water uptake, bigger, healthier plants
- Enriched with a specially formulated plant food that gradually releases nutrients for up to 9 months
- Water less often with the included Coir / coconut fibre (Canada only) or Polymer Gel (USA only) that increases water holding capacity