The older a biological fertiliser gets, the less biological activity it will have. However, it will still deliver minerals and trace elements to plants, even if it’s past its prime. Avoid using biofertilisers if it’s “off”. A strong, foul odour is a clear sign that it’s no longer effective. If your biofertiliser is “off”, you can safely discard it by burying it in the ground or adding it to a compost pile.
