Fertiliser

I initially spread a thin layer of blood and bone about 100mm below the final surface of the potting mix and then fertilise weekly with 5ml/L of the seaweed. This seems to have been sufficient for my first run of crops but will endeavour to get some dry horse shit from my old man’s work to mix in before I start the second run.

There is too much nitrogen. Grass is a leafy, herbaceous, non-blooming plant and can use the extra nitrogen. Bonsai are woody plants with different nutritional requirements. Balanced houseplant fertilizers are recommended. Flowering & fruiting bonsai benefit from bloom booster fertilizers.
There is not much point in using this fertilizer if you have to add to it. Bloodmeal, fish emulsion, and bonemeal are also high in nitrogen. Seaweed extract is more of a tonic and contains a negligible amount of fertilizer. Besides, if you use bonemeal & bloodmeal outdoors, dogs, cats, & carnivorous wildlife are attracted and will wreck your plants.