Hi Daniel

Snipped

Let's just say that now they are looking awful. I water them pretty
often, probably twice a week. I hadn't realised just how badly they
were doing till I compared them to the third box which I trimmed but
left in its plastic pot. The one in the plastic pot is green and
healthy. The two which I have transferred are brown, slightly
dessicated and look very unwell.

My great gardening triumph is turning to disaster before my eyes.

Any thoughts?

Whilst box don't like to be in dry soil, are you sure they have sufficient
drainage and aren't sitting in water? I'd be tempted to lift one of the
plants and see if the roots are wet, and whether there is any root growth.
You could also check that the roots have started to grow out into the
surrounding compost, and not in a spiral as they may have been in their old
pot.

My first thought is that the metal planters are heating up the roots
so they dry out. I know it's hot at the moment, but not that hot
surely? The box are in part sun part shade. Probably in sun 50% of the
day. Should I bin the zinc planters?

I doubt very much that it's the planters heating up (I'm assuming that they
are largish planters and not the small 5inch type zinc pots). Box don't mind
sun or partial shade so I don't think that's the problem either.

I also wonder whether it is worth standing the planters in a dish to
keep them wetter rather than letting excess water drain out?

I added some top soil to raise the level of the earth in the container
and to hopefully retain more moisture. Too soon to say if that has
helped.

Should I feed them?

Don't feed them - it sounds like they are stressed enough, feeding them will
only make them worse.

You could always take a few cuttings off the plant that is doing well. Take
4 inch cuttings, removing the bottom couple of pairs of leaves and push into
a pot of soil or compost, and leave in the shade.

Hope this helps.

Regards

Nick
http://www.ukgardening.co.uk