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The story: I have bought a few sacks of "Plagron Royal Mix" here in Chile. This soil is supposed to be sufficient for my "tomatoes" for roughly six weeks. After four weeks in the soil I noticed problems, which seem to point to under-fertilization. Since it was time to repot anyway, the plants received roughly 50% fresh soil in a bigger pot, but the symptoms are worsening. Over-fertilization, while not impossible, seems unlikely. Before repotting, I rinsed the soil to remove excess fertilizer. (As recommended by the manufacturer)

Now considering the trip from Holland to Chile and that it's not really a hot product here, I cannot rule out that the soil was stored for a significant amount of time possibly even under adverse conditions. There are no dates on the sack.

If an organically pre-fertilized soil (peat, fibre, worm castings, etc.) is stored for a longer period of time, how does it change? Will it reduce the potency of the fertilizer? Can it have other harmful effects on plants?

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  • Just for the anecdote: The actual problem wasn't the soil, it were cheap plastic products. It was the outgassing of Phthalates that was killing them. The effects can be mitigated a bit by feeding more nutrients, hence the red herring.
    – Mantriur
    Aug 11, 2019 at 20:34

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The main problem with long-term storage of potting type mixes is that they can dry out to the point where they're almost impossible to re-wet, this can also result in nutrients becoming locked up and unavailable to plants. And tomatoes are hungry things, also none of the ingredients you mention (apart from to some extent - the worm castings) contain significant nutrients - you'll benefit from a foliar feed being sprayed or applied with a water-can onto your plants about weekly.

rewetting potting mixtures are best done before planting into them, one way is to slowly soak the mix in water with a little dishwash added (then let it drain) - this breaks down the wetting resistant agents in the 'soil' particles. Ideally next time you would obtain some clean, weed-free real soil and mix it 50:50 with your dishwash wetted potting mix.

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  • The ingredients are a bit misleading, I just copied what I could find on a shop page for the soil. It is a very hot soil with an EC of 2. The soil was in plastic bags and moist. I've added some fertilizer two days ago, and the problems seem to be in regression today, which points to an actual lack in nutrients, which should be impossible ... The soil having been stored too long is the only theory I can come up with to explain this lack of nutrients, hence the question. :)
    – Mantriur
    Nov 17, 2013 at 17:56
  • Yes, that's what I meant about it being dry; with enough time the soil particles become almost waxy and so hold onto their nutrients within.
    – nigelc
    Nov 17, 2013 at 18:51

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