Not enough data.

What do you mean by saplings? These are not trees. Were these transplanted? Or grown from offsets? or purchased as fully-rooted plants?

They looked baked by the sun to me. Did you leave them in the sun at all? These need shade. What have your temps been like lately?

@Ken, the clay breaker stuff is this link

No I did not do a soil test.
But during digging it is pure sticky clay below. (I usually water the place before digging)
I have no idea what is native soil perk to be honest!!

It is second half of the summers here in Sydney. But the location gets morning sun only. And these guys were in location where they are dwarfed by other plants. I had posted some pics of the location in this link

@Dave:
I bought them online and they arrived as tubestock. Maybe sapling was the wrong word !! They are small and have roots.

It is summers here. We have been having 90F plus temperature for almost the whole month with few days crossing 100F too. But these guys are in location where they get only morning sun.

Even here in the U.K. this shrub is recommended for a shady position so they definitely don't want too much sun. Regarding the planting I think you have rather gone overboard. This plant is a tough unfussy creature which will grow in pretty much any soil. They are used in places like supermarket car parks and school grounds. It copes with dry soil and urban pollution. It would be best just being plonked straight into the ground without all the potions.

I agree with floral - a very tough, undemanding shrub that doesn't require excessive amending and very little fertilization, just a fair amount of shade to make it happy. In fact, it is one of the few shrubs that is happiest in dry shade, an always challenging planting situation.

Well, morning sun at those temps could have done them in. They do look quite baked to me. They may have been grown in a shade house up to this point, and were not ready for any amount of sun.

In future plant shrubs in existing soil without amending or plant in more favorable soil dumped on top of existing soil without blending the two together.

Or for small growing kinds dig out sections of existing soil, replace with more suitable soil. The wider the sections the better.

But do not plant in individual holes or pockets of amended soil.

Thanks for the replies. I think it was a combination of too much fertilizer and sun which did them in. It's 9.30 morning here and it is hot. And these guys are getting roasted in morning heat!!!

The remaining two will stay covered in the first half of the morning. Till the summer passes.

Won't they boil under a black pot in the sun?

Due to what kind they are they are never going to adjust to full sun exposure in a hot climate. Persisting plantings of sarcococca here in our cool climate do include ones in sunny positions but these always have poor color.

Hmm...Maybe I will relocate them then. This is a difficult spot. In summers it gets heat till 10 in morning. And in winters no direct light. Any suggestions for a small low growing plant. Preferably fragrant like this. Or having colourful flowers.

Maybe try Garden Web Australia forums.