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Post by Ron on Dec 12, 2016 22:28:01 GMT
Did you know that commercially bought compost when stored degrades over time? Plain compost isn't too bad because it contains minimal nutrients anyway, but compost with added nutrients can become harmful to your plants in time. So if you have the odd bag or two left over or you buy your compost before you need it, you should be aware of the risks. It takes about three months for it to happen but you don't know how long it has been stored by the garden centre and manufacturer, so it could be a problem sooner.
You need to restore the balance of nutrients before using the compost if it has been stored for a long time. Of the macro-nutrients, the biggest loss will be Nitrogen (N), followed by Potassium (K). Little Phosphorus (P) is lost. Calcium (Ca), Magnesium (Mg), Sodium (Na) and Sulphur (S) are also lost, which results in an accumulation of Copper, Zinc and Nickel which can become toxic when the other micro-nutrients are not present.
Fortunately there is a common fertilizer you can add (read the label for quantities) which is that added to lawns in the Autumn. Look for a ratio (N-P-K) of about 20-0-10 with added micro-nutrients.
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Post by andy on Dec 13, 2016 5:58:57 GMT
I wouldn't personally be looking at a fertilizer so high in nitrogen to add to an all purpose compost (unless you were growing foliage plants). A more balanced 7-7-7 that is found in Growmore is far better in my experience.
I re-use 50% of my old compost every year by mixing it with fresh and then adding a handfull of Growmore to it which is a controlled release fertilizer.
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Post by Ladygardener on Dec 13, 2016 7:06:07 GMT
I use growmore as well, it does work for me.
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Post by Ron on Dec 15, 2016 19:38:27 GMT
Growmore is fine stuff but perhaps I didn't explain myself well, that's not the point. A basic compost is low nutrient, you would add fertilizer according to your needs. One with added John Innes or a John Innes based one uses loam which holds nutrients well. You can re-use these without a problem. Many come with added nutrients though and are not John Innes formulations, especially peat free composts. It is these I was referring to. After time these nutrients become unbalanced. Adding a 10-10-10 type fertilizer will not correct it, you will still have a surplus of Phosphorus and more Potassium than Nitrogen. A 20-0-10 (or 10-0-5, the ratio is what matters) formulation will correct this.
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