you should feed apple trees just before they begin to grow again for this year so February is a good time. Apply a good general fertiliser but not too strong as they do not want to be over fed.
As for the rest of your plants, depends on what they are but most will benefit from some feed as they begin to grow, some well established plants probably wont need any.
I always feed my fruit trees at the end of February, giving them a couple of handfuls of potash, worked into the soil, which will encourage fruiting, rather than growth.
The remaining plants I feed with a good general fertiliser as they begin to grow. As flowering bulbs die back I feed them, again with a general fertiliser to encourage flowers next season.