Maybe you regret your new haircut, or would like your hair to be a little longer for a party. There are a number of practical methods to accelerate your hair growth. If you want your hair to grow a little longer within a week, try enriching treatments such as a warm oil scalp massage. Try to minimize stress on your hair and eat certain nutrients that are known to help your hair grow (such as proteins and biotin). There are limits to how fast your hair can Regrow hair naturally in 3 weeks, but if you give your hair a little extra love, at least it will grow as fast as possible.
Regrow hair naturally in 3 weeks in following steps:
1.Give yourself a scalp massage with warm oil. You can do a scalp massage with warm natural oil to improve the health of your scalp and stimulate hair growth. Oils such as coconut oil, olive oil, jojoba oil and argan oil are all suitable for a scalp massage. Keep in mind that it has not been scientifically proven that this makes your hair grow faster. 
- Start by heating the oil in a pan on the stove or in a container of boiling water. Test the temperature of the oil first to make sure it isn’t boiling hot; it should be nice and warm, but it shouldn’t damage your hair and scalp.
- Massage the oil into your scalp with your fingers, using slow, circular motions. If your partner or a friend is nearby, you can also ask them to help you with a massage. Massage your scalp for fifteen to twenty minutes.
- Then apply the oil to your hair ends and let it act for 30 minutes. Then shampoo your hair well, perhaps more than once, to remove the oil.
2. Make a hair mask. Give your hair some extra attention and stimulate your hair follicles by using a hair mask once or twice a week. You can make it yourself with natural oil, or buy a hair mask from the store. 
- Mix 1 cup coconut oil with 1 tablespoon almond oil, 1 tablespoon macadamia oil, and 1 tablespoon jojoba oil. Apply the hair mask to damp hair and leave it on for 10 minutes. Then wash your hair as you normally would and apply conditioner.
3. Try a castor oil treatment. Castor oil is known for its beneficial effect on skin and hair.  Using a castor oil mask will help your hair grow faster and become healthier. 
- First massage your scalp with castor oil and then apply it throughout the rest of your hair. Put on a plastic shower cap to keep the oil in place. You can put a towel on your pillow so that no oil gets on it.
- Let the oil soak in all night. The next morning, wash your hair as usual to get all the oil out.
4. Use an apple cider vinegar rinse. Apple cider vinegar can be very effective at rinsing dirt, oil and care product leftovers from your hair. You can use apple cider vinegar on the non-shampoo days as a natural alternative, or you can use it after your shampoo and conditioner to rinse out your hair. 
- Put two tablespoons of vinegar in half a liter of water and rinse your hair with it. Although it can smell very strongly of vinegar, this smell fades quickly.