Plant This

Re: EDITOR 18 Jul 2011 - 10:25:00 AM

It's possible their particular micro-climate is a bit different – sun, water, wind or something. But I get the feeling it's more likely that those two were just weaker stock – maybe more pot-bound, water repellent and harder to establish. As a test, give them a bit of a shake from the base of the stem to see if the plants still rock within their own root ball when the roots should have spread out and locked the plants in.
Remedial action could include digging them up, teasing roots out root pruning if they still look salvageable, replanting and giving special watering and fertilising, pruning back the others so they don't out-compete the weaker two while they catch up.
But the quicker answer would be to replace the two with healthy specimens of a size to match the others.