A vegetarian diet can provide enough iron to be healthy. Vitamins and minerals matter because they help absorb iron: the first and foremost useful is the plain vitamin C. You need to eat foods that are rich in vitamin C and foods that are rich in iron at the same time. For example, eat cereals with added iron in soy milk, or spinach salad with orange and sesame seeds. You can also find foods that contain both vitamin C and iron together: broccoli, potatoes. There are also plant based meats that are rich with iron.
Of course, not only vitamin C stimulates the absorption of iron. Copper plays an important role, Magnesium, Vitamin A, D, and the vitamin B complex. Your body is a living machine that adapts to your daily iron intake constantly: if it is too low it increases the power of absorption when it is in excess is absorbs less.
It is a good idea, and many doctors recommend it, that you take some iron supplements while you are on a vegan diet. More often than not these provisions are more than sufficient to protect you from anemia. Pregnant women and children should get more iron. To cover the special nutritional needs, they need an omnivore diet.
The recommended daily iron intake for women is of 15 mg before menopause and 10 mg after menopause. Men need about 10 mg, so you must be careful with excess iron, which can be harmful. You have to be very careful with your iron intake if you plan to become a vegetarian.