Most of a plants food is produced by photosynthesis, fertilisers are more in the line of 'vitamins' or 'supplements'. So just as vitamins and supplements keep our systems running smoothly, so do fertilisers with plants. Generally it's best to give weak solutions of fertilisers more frequently rather than to give higher doses at longer intervals. The products will have instructions on mixing with water and rates of application. If you follow those you shouldn't go wrong. But you can make the solutions weaker and apply with each watering. The big thing to remember is that over your winter period the plants will be less active and need less water or fertiliser. Also, over time you get a build up of mineral salts in the potting mix. This needs to be flushed out from time to time. Just flood the pot and let the water run through. The soil should be fast draining. Organic matter in the potting soil breaks down and you're left with a heavier water retentive mix. The solution to that is to repot with new soil.