Pre-heat the oven to 200ºC non fan / 180ºC fan / gas mark 6.
Put the carrots, parsnips, onions, potatoes and garlic into a large roasting tray or, if you don´t have a tray large enough, divide between two.
Drizzle the oil over the vegetables and mix well. Scatter over the rosemary and thyme and season well with salt and black pepper.
Cook for 30-40 minutes, depending on the size of the vegetables, stirring once half way through cooking.