When cooking vegetables an easy tip for remembering the water temperature is:
Were they grown above ground or below? If they were grown above ground (broccoli, green beans, kale, etc) in the warmth of the sun needs to go into hot water.
If it was grown below ground (carrots, potatoes, garden gnomes) in the cool earth, then it needs to be cooked in cold water or at least started in cold water.
Fun Fact about Cooking Potatoes in water: If you put them into hot water, the heat will cauterize all the starch by the openings on the surfaces and they will be gummy and unpalatable.
Interestingly, these potatoes can be dangerous to diabetics because the sugars normally released in cooking remain trapped inside.