Supposed to be good as a compost activator too. BTW, Wilkinson's have got 4kg boxes for 2.99 (sorry to go off-thread!)
Bless you for going off-thread. Now added to my Wilko's look-out-for list! 8)
For me, it's as tony said...feeding & putting into good heart the soil or for the plant?
For the soil, it doesn't add bulk or humus, the source of organic matter, but as a supplement to..
Therefore I follow the guidelines in my booklet, bulk up the soil during the winter before planting then add J.Arthur Bowers (only cos I get boxes cheap in the sales not cos I'm particularly endorsing that company) for the patch - be it bone meal, ammonia, potash, sulphates etc....
Then, when I plant out, I do as others, above, and continue through the growing season.
Might have got it wrong, but hey! works for me ;D