The easiest way to do is to collect the outer peels of the onion which are to be discarded (while cutting the vegetables) and blend them. Put them in a sieve cloth and extract the liquid. Apply the liquid on your scalp. You can also apply the blended onion paste directly too. The smell would be stinking so you have to wash your hair after that. Keep it on for half- hour or as long as you can and then wash off with a mild shampoo. Do this as many times as you can in a week and you will see results within a month or two. You have to be consistent with the treatment. You can also add fenugreek paste to condition your hair simultaneously. Try to be innovative. Add eggs, honey, fruits, oils or anything else you are in a mood for.
Another advantage of applying onion on your hair is it will give you hair a nice coppery shade. It makes your hair look glossy. But, if you want to maintain the natural color of your hair, mix the onion blend with adequate amount of mustard oil. The oil will prevent the color lightening caused by onions. And, you can increase your daily consumption of onions for a beautiful hair.