More on watering...
Yes, they probably dried out a few days ago but the results are just being seen now. The problem is that the tiny root hairs, the ones that absorb soil moisture, dried out and prevented the plant from taking up its required moisture.
In the meantime, the plant was transpiring through the leaves so naturally there was going to be a problem. Once the damage is done, you can’t quickly resolve it!
Native plants that grew naturally from seed match their water requirements; only as much foliage is grown that can be supported by soil moisture. The general system of transplanting container-grown stock into natural ground (or a larger pot) has a critical point where the requirements are not matched - this is the crucial time.
With new plants going into the ground, make sure you closely watch the soil moisture levels right against the original root ball. It’s quite possible for this supplied moisture to be repelled by soilless media and drain away into the surrounding soil. The plant appears to have been watered but little water actually reached the roots. You can see this on sandy soils that have dried out; splash a hose over the surface and the water beads up and fails to percolate in.
Virtually all ornamental plants are nowadays grown in soilless media. This can also be water repellent (hygrophobic) if it dries out. The best practice is to direct the gentle stream of water for say, five seconds, to the root ball of your new plant, move along to the next one and to the end of the line then come back to the start again and repeat. The first watering breaks surface tension and creates percolation pathways so that the second watering soaks in better.
Watering myth #356. ‘Don’t water in the midday’. Some say that tiny water drops magnify the sun’s rays. Well, in 45 years of growing millions of plants we have never seen this happen! If a plant is dry, water immediately. Best time for watering is in the morning, the worst is late afternoon. If you water then, you risk creating moist conditions favourable to various fungal diseases.
Don’t forget to mulch! Mulch minimises evaporation and buffers soil moisture and temperature. 75mm of bark chips, ‘forest blend’ or tea tree mulch works well. More on mulching soon.