I love emu bushes too and have several different types. They're just lovely in bloom and out, aren't they? 'Easter Egg' is my favorite because of the multi-colored blooms, though I have plenty of 'Valentine' too. I love its delicate foliage and dark stained stems and leaf bases, plus those kooky February blooms. Rosemary is always a winner too--I just have one plant in a pot that I've carted around for many years garden to garden.

Anyway, sorry to hear about issues with yours on the north side of your garden. Are they still in full sun there? I ask because it sounds like they might, just might, be getting just a bit more water than they want? In full sun that amount might be fine but if the ones in the north side of your garden get some shade it might mean that it's more water than they want compared to their full-sun siblings. Just a thought, though.

I give my full-sun emu bushes ('Easter Egg', 'Valentine' and others) a deep irrigation once a week in summer and once every other week in winter and they're growing like crazy and bloom each spring, so that just makes me wonder if yours are getting just a bit more water than they want IF they're getting some shade?

I wouldn't change a thing about the ones you say are thriving in the south part of your garden (if it ain't broke, don't fix it, LOL) but maybe cut back a little on the frequency of watering for the others? Let's see what everyone else thinks and suggests too.

Oh, and superthrive never hurts in my opinion, so I'd go for it.

Let us know what you decide, and do, and how it turns out. Eremophila (emu bushes) really are great plants and deserve even more of a following than they have.

Take care and keep us posted,
Grant

You may want to make sure your emitters are working properly, too. They sometimes get clogged with debris.

Half a plant dying makes me think somethis is happening below ground as in damaged/diseased roots. Too much water in our heat and humidity can set up fungal and bacterial rots.

Both rosemary and eremophila are very drought tolerant. Its always better to water deeply but infrequently allowing the soil to dry just a bit before the next application. Grant's schedule sounds good. My eremophila gets water about once a month in the winter and once every two weeks in the summer, but I apply 5 - 6 gallons each time.

Here's a link to the water needs of citrus.

Here is a link that might be useful: Irrigating Citrus Trees