One of the most useful rules for cooking vegetables is this: if it grows above the ground (stems, leaves!), start it from hot; if it’s grown mostly underground (roots, tubers!), start from cold.
This is especially useful to remember for boiling and simmering: broccoli should go in boiling water, spuds should be brought up to boil. But it also applies to roasted vegetables. Your underground friends could benefit from a slower start – like a parboil, or a cold oven.
