[Jim Ford]

Unless you're growing for maximum profit per hectare, I don't think you should really worry about speciality fertilisers - but to bear in mind the general rule:

Nitrogen for leaves eg. cabbages lettuce.
Phosphorus for roots eg. carrots and potatoes.
Potassium for flowers and fruit eg. tomatoes and strawberries.

So that means you can usefully put wood ash on tomatoes and IIRC, compost some bracken, which is high in potash.

Also with toms. keep watering to a regular regime - don't let them dry out and then drown with water, which can cause them to split or suffer from 'blossom end rot'. Toms. can also suffer from magnesium deficiency which show itself as 'interveinal yellowing'. The remedy for this is to spray with a solution of epsom salts.

If you're growing in the ground in a greenhouse, over the years you _will_ find they grow less and less vigorously. This is caused mainly by a build up of viruses. The only cure for this is to dig out and replace the soil - and I mean _dig_out_, which means to a depth of at least a couple of feet or more. Growing in grow-bags avoids this problem (which is why it's done commercially) but introduces, others mainly to do with watering.

Jim