A Word on Natural
vs Chemicle Fertilisers
Rule of Thumb
The general rule of thumb for using chemical vs organic fertiliser is to use:
chemical/synthetic fertilisers for plants in pots
eg Triabon, Nitrophoska, Osmoform
So you need to use organic matter based fertilisers in your garden. This is because: the more worms and organisms you have in your garden, the better off your garden will be. And when you fertilise the garden, you are in fact 'feeding the worms' something organic which they can eat! They in turn, break down the organic fertilisers into a form that can be taken up by plants.
Yes you can use manufactured fertilisers on plants in the ground - but the problem is that the chemicles feed the plants directly and not the organisms. So the worms etc will eventually die or move elsewhere in search of food. These orgsanisms are vital for long term plant health, aerating the soil, and giving it good structure, and for forming part of your garden's food chain. So if you use chemical fertilisers in your garden, your plants may do well to start with; but longer term the garden will not thrive.
However: these organisms, like worms, don't come in potting mix - so nutrients in an accessible manufactured form have to be added to plants in pots. So it is OK, in fact preferable, to use chemical fertilisers for plants in pots.