Arawn was stunned by Evanna's first attempt at using her gift. He wanted to test the strength behind her power; he never expected the stems of the flowers to grow healthy once more. She was not even trained, and after a few seconds of hovering her hand over the plants, he saw the small gold sparks leave her hands and pour into the plants' roots.
When an elf first retrieves their gift, they need to train their bodies to wield it. It takes a great deal of energy, so like sword fighting, it needs to be practised each day to get better. The skill and strength used behind it will improve. Evanna seemed to have some power behind her already; she just needed some direction in calling on the gift, only wielding enough of the gift dependant on the task and how not to burn out. They would definitely start on small tasks such as this.
