Ixora is very sensitive to alkaline conditions, which can be present with any planting close to concrete - house foundations, walkways, drives, etc. Concrete will leach lime over its entire lifetime and the lime creates alkaline conditions that result in chlorosis or the bleaching out of foliage color.

You can attempt to increase the soil acidity by garden sulphur applications or water the plants with acidified water. Supplementing with chelated iron could help as well.

or just remove it .. .and train the second one over that way ..

or replace it with anything else ...

btw.. just fyi.. straight down pix are weirdly disorienting ... i dont get the first pic ... are all the plants but one affected??? .. if so ... i might just cut bait..and try something else ... a lifetime of soil amending gets old.. and expensive.. quickly ...

also.. i get you dont have much of a front lawn there.. but foundation plants are planted to hide the foundation .. NOT ON THE FOUNDATION... and that is part of your problem ... they are just too close to the house ...

in that vein.. perhaps you dont need the lawn at all.. and when you plant something else.. just move halfway out between the house and what i presume is the sidewalk ..

also.. the lawn look a bit limp.. which makes me wonder.. how you water that whole area ... are your shrubs properly watered ... and lawn irrigation amy not provide that ... so im thinking.. you might havbe problem on top of problem ...

btw... where are you.. big city name ... and what direction does this planting face ... based on your shadow in the pix.. im thinking it might be south facing ...

ken

Surface applications of garden sulfur usually don't work very well; they're often lost to the air as sulfur dioxide (smog), and the bacteria that reduce it to acidify the soil simply aren't active in alkaline soils (which, since that's paling out, you have).

Fortunately, there's an easier fix for that...and no, it's not aluminum sulfate, which I never recommend (it's toxic if, perchance, the soil should ever go moderately acidic...unlikely, but possible). Overall, there's rarely any reason to add a potential toxin.

You can pick up any mix of ferrous sulfate (garden iron) and mix it at any rate of 1 -2 ounces per gallon. Iron's not toxic until ridiculous levels (50,000 PPM) and not until absolutely insanely acidic pH (<5).

Pour it on the plant, watering it down to the deep roots. Let that sit. It'll both acidify the soil a bit, which will allow any sulfur you've added to begin to work (aha!), wash that sulfur in (double aha!), and add iron to the soil. It may do the entire job all by itself if the issue is minor.

With a little of the rest, you can add just a teeny bit of soap (maybe 1/2 to 1 tsp per gallon of a dish soap or other liquid, non-antibacterial hand soap, just enough to get it to stick) and spray the plant to apply a foliar app of iron.

No, you won't burn the plant from any imagined phytotoxicity of soap, it's far too little and your Ixora is not on any list of susceptible plants.

Interesting that every single science-based website one can find on acidifying soil recommends using garden or elemental sulfur worked into the soil as the most efficient and effective way to lower pH. And NO mention is made about the lack of necessary bacteria in an alkaline soil to accomplish the conversion into sulfuric acid. And why should they be? Soil bacteria tend to decline and become less active in highly acidic soils!

I guess some like to think they know more about soil science than they actually do :-)

It is also important to note that concrete leaching does not alter soil pH significantly but only to the point where acid loving plants may struggle accessing nutrients, resulting in chlorosis.