i am know expert but i believe you feed plants etc when there comming or out of dormancy . im fairly sure you dont feed most seeds as they have like an egg got food for the first bit of there life . i would get a feed you mix with water and as you say just water in the general area . it should say on the directions what and when you need to do this . to much food can be worse than not enough . i hope this helps and im sure youl get a better answer soon .

Make sure that the mulch is not right up against the stem/trunk of the plants as this may cause them to rot. You can mulch them now while the soil is still moist and sprinkle your chosen fertiliser around (follow pack instructions as Noseyp says) in a few weeks time. I generally lightly rake in the granules or mix some into the bottom of the hole when planting new things.

With trees and shrubs, feed from 15-70 cm inside to 15-70 cm outside of the "drip line"--that is, right under the outer edge of the foliage. Compost or mulch should start 15-30 cm out from the trunk, out to the drip line, plus a little beyond. I would apply granular fertilizers a week or two before the estimated date of sprouting, and liquids when you first see signs of sprouting. since they work faster, and wash out sooner. Most granular feeds are better scratched into the soil a little. If on a lawn, rake the lawn gently to knock the granules off the blades. Be sure to water deeply after using granulars, unless there is a VERY heavy rain after--3 cm or more! With herbaceous plants, lightly and evenly feed the entire bed.

Thanks for the info folks. I wondered if, in the case of Hostas for instance, whether it would be good idea to mulch the area in the Autumn while they are dormant to preserve the moistness of the soil and allow them to grow up through the compost in spring. Bearing in mind what has been said about keeping the compost away from the stem of the plant, might this cause some damage to the emerging plant?

Probably not so much for Hostas, since they are forest plants, and so used to leaf litter. The main problem might be giving too much shelter to snails and slugs.

Thanks Tug, I hadn't thought of that because (fingers crossed) we have no problem with slugs or snails which I put down to the presence of loads of birds in the garden who are forever rootling about in the leaf litter and I am constantly finding smashed snail shells on the rocks and pebbles. Needles to say, we encourage the birds as much as we can.