If you keep the area weed free you will get a higher success rate and better growth than if young hedging plants or trees have to compete for moisture, nutrients and light with grass and weeds.
A handful of fertiliser in spring never goes amiss.
Mark any losses in summer (when the plants are in leaf) so that you can replace them the following bare root season. It is inevitable that you will have some losses in the first 3 years (a small minority if planted well) so you should budget and plan for this.
If you have used spiral guards, you can spray herbicide to maintain a weed free area but you still need to take a lot of care not to get any herbicide onto the hedging plants or tree saplings. Use this time to ensure that all spiral guards are still upright and fully protecting the plant. You need to leave the spiral guards in place for 5 years, after which they can (and should) be removed and the usable ones recycled on another length of hedging.
If you have not used spiral guards, the only viable option is to use weed suppressing fabric but this is more difficult to maintain over several years and in our view not as effective (which is why we do not sell it).
Trimming the tops of all hedging plants other than evergreens will help them to bush out. Do not trim when birds are making their nests or have young in nests. Whilst you can trim from 31 July onwards, we recommend trimming in late winter so that there is a winter larder of berries and seeds for birds and other wildlife.