Each spring the Cherry Blossom trees that line DC's tidal basin burst into fluffy white blooms. After living on the east coast of the United States for over a decade I finally made it down to DC to see this stunning event. Making the trip during peak bloom ensures you will see the most blossoms. This happens for two to seven days sometime between mid March and early April, depending on the weather.
In order to find out when peak bloom would occur, I kept on eye on the National Park Service's forecast. They usually issue their first prediction in early March. The prediction can then change depending on the weather conditions.
This year the prediction changed by a week twice. If you want to see the blooms at their peak it's best to make travel arrangements that are flexible or can be changed last minute. I am lucky to live a car, train, or bus ride away from DC which makes last minute trips much easier. If you are traveling by plane make sure to purchase your airline or booking website's travel protection to allow for last minute changes. If you do need to change your plans and your hotel is full, apps such as Hotel Tonight are great for last minute bookings.
I suggest going to Tidal Basin early in the morning when less people are around. The crowds get very large, especially during peak bloom. This makes taking photos a bit challenging, but just be patient. People were very friendly and conscious of fellow photographers trying to get the perfect shot.