No Veggies

It's really difficult to feed veggies to my son. I am trying to cook many kind of vegetables for him. But the moment he taste the veggie with his tongue, he will throw it out again. The only thing that sometimes worked is by blending the vegetables and mix it with the food that I gave to him. For example, I normally blend spinach then mix it inside the spaghetti sauce that I serve for him. I think he can not taste it easily if I do like that. I don't know until how long that I should blend those vegetables for him. Does somebody has advice for me?