I'm out in the garden most nights, and get to prune, and dig and water and
feed, so I can't think what is happening. I've read the earlier posts
about dying conifers, but would like to know what I might be doing wrong.

Had some conifers (spreading leylandii) put in early spring to get a garden
boundary going. Most of them did pretty well; though one of them dried out
by mid march and I uprooted it and put it in the shredder, replacing it with
another from the garden centre (a slightly different variety, but thriving
none-the-less). Recently however, another of my conifers suddenly went
brown and the needles started dropping.

I cut it back, fed the plant, and sprayed it in case mites had got to it,
but it went downhill rapidly and within two weeks, I had to dig it up.
I've trimmed it and replanted it behing one of my healthier greener
leylandiis, in case something magical happens, and this time, I replaced the
gap with four newer conifers.

And then suddenly only two days ago, another of the conifers planted in
spring has taken a nosedive. If the other two are anything to go by, I
don't hold out much hope, although I intervended on Tuesday night when I
noticed the first discolouration and the slight droop.

Why is this happening? Is there anything that I can do to prevent healthy
looking green conifers from drying out and dying within what appears to be
days?