Where do you live? We can't tell if you are overwatering unless we know where you are and what the conditions are. In my climate, for example, it would never be necessary to water this plant at all. Nor do we know how much water ids being delivered in those four minutes. It is usually better to water very thoroughly less often than in frequent small quantities. Of the parents, E amygdaloides is native to dry areas in woods here (Its common name is Wood Spurge) and E x martinii is a cross between E amygdaloides and E characias, a Mediterranean native. So unless you live in a very dry climate, chances are you are indeed overwatering. What does the soil around the roots feel like?

It would also help to know where you are located. The xmartinii hybrids are not the hardiest of selections and Blackbird in particular seems a little iffy. Even in my very mild Mediterranean type climate, Blackbird doesn't hang around long and most local nurseries no longer carry it. The other xmartinii hybrids seem to be much more robust.

I would agree with floral that this plant generally requires very little in the way of supplemental irrigation, although all my euphorbias are mixed in with other perennials and shrubs and get routine watering in our dry summers. They will tolerate this just fine as long as drainage is sharp. But even so, at only 4 minutes a session 4 days a week I can't imagine that it is getting too much water - that's barely enough water to keep anything alive!! If only in the ground two months and therefore not established, a couple of deep soakings would have been much more in line for the plant's needs than just tickling it with water for a few minutes a few times a week. I think the plant is suffering from a lack of water, not too much!

insert finger.. or use a tablespoon.. and GO FIND OUT IF THE SOIL IS WET OR DRY ... 2 to 3 inches down ...

transplant shock is a great possibility ... with evergreen plants.. it can take time to 'show' the damage ....

asking us to figure out how your drip system works in your soil is impossible ...

flora said in england.. she would never water such a plant ... i bet she would have.. at planting ... did you water in the transplant well??... or did you just rely on the drip .... btw.. what type of drip system ... an engineered one.. that distributes evenly .... along the entire run ... or the recycled tire type???

what is on the side away from the house ... a brick sidewalk ... that could be frying it.. more than the full sun reflected off the house ... it could also retain the heat long into the night.. not allowing the usual cooler night recovery period ...

ken

is there damage on the back side .... the part that is shaded by the plant itself ...???

ken

The fact this plant is on a drip system and only receiving water for 4 minutes at a pop pretty much confirms my suspicion that it is not receiving enough water :-))

Drip irrigation systems are typically run far less frequently than a pop-up sprinkler system, at the most once or twice a week. And the duration of the watering period will be dependent on the size of the emitters but is typically in the 30-90 minute range. 'Low and slow' are the key words with type of irrigation system, or IOW, infrequently but for an extended duration. You want the water to penetrate fully down through the soil profile to adequately hydrate the root system and 4 minutes - even as often as 4 times a week - is just not going to cut the mustard!!

Euphorbs are tough and this one should recover with adequate moisture but I think you may need to revisit the programming of your drip system to make sure you are providing all your plants with the water they require.

insert finger.. or dig hole.. and FIND OUT.. at depth ... soil moisture ... sounds like you are still guessing.. winging it ...

ken