How much tomato fertiliser to use

Can anyone please tell me how many tomato plants a watering can full of Tomato Fertiliser (made up to the strength recommended on the back of the bottle) should do.  The bottle says water onto roots until 'completely saturated' so I have no idea whether I am giving them enough.  Also should I water before feeding?

My toms at home are in plastic patio type pots in the greenhouse. I like to feed just as the surface is drying up a bit, and give enough feed to get a small amount of run off. That way you know all the roots are fed from top to bottom. I use about 10ltrs of feed per 3 plants.

Totty

Thanks a million folks, I think I am under feeding (kinda guessed as I wasn't seeing much results from the feeding).  I have been using 10 Ltrs of slightly understrength feed on 10 plants in the boarder and the soil is usually wet when I have been feeding.  I have only been feeding every 10 days or so.  I will let the soil dry out a bit and I will go onto a two weak feeds a week regime and see how that works.

Would I still need to feed my toms if the are bordering a very rich in manure (old, good stuff) bed that has my beans and sweet corn? The odd plant seems to have roll leaf ... But is still fruiting nicely.