New hedge and Dogwood.

With huge thanks to Kristen for a recommendation on my 'hedge' thread, I have ordered some plants from Ashridge trees.

I ordered some Italian Alder to make a 6ft hedge in the front garden. Also 6 cornus - 2 yellow stem, 2 scarlet stem and 2 variegated leaved red stem - and 3 cherry plum trees.

Can anyone advise me if I've done this right, and also views on cutting back.

With the alder I've planted just under 1.5ft apart. I've planted with rotted horse manure (treated from sealed bags from garden centre) a bit of compost and the soil from the hole. I've also sprinkled a bit of growmore around. We bought 90-120 cm plants and they have advised on the phone today that I cut them down by half. I can't help thinking we needen't have bought big ones if we do that, but common sense says it will come back good and strong and the age of the trees should help with that. How much growth can we expect this year?

The cornus I have planted in the same way. But in a loose zig-zag and mixed the varieties up. I've given them lots of water, and again the advise is to cut back by half. I had read on another site that cornus should be left for first year and then cutback to neck next spring. Does anyone have a recommendation? The lady on phone said they would bush up more.

Again how much growth can I expect from cornus this year? They are 80cms at present.

Would love some advice!