If they're in the ground, just follow the usual rules. Apply a general purpose fertiser such as Osmocote or Growmore in spring, lightly forking it in, and incorporate humus rich material such as well composted animal manure and the like at least once a year. You can use it as a mulch once you've applied the chemical fertiliser if you like instead of digging it in. If they've only been planted recently, you will need to keep them watered during dry spells over the coming months, particularly the witch hazel.

If they are newly-planted, then I would take Bamboo's advice and pay special attention to watering. Water regularly and a good mulch will help. I would grow them hard for the first year and perhaps feed only with a potassium fertiliser like sulphate of potash if you really must.