This is excerpted from the Urasenke website.

Question and Answer with the Oiemoto

Question: No.6 Why do we use the tsurigama in March?
Answer: There is no reason that the tsurigama must be used in March.
The tsurigama is a kettle that uses a chain hanging from a hirukugi on the ceiling. We basically use it from the equinox of March until the middle 10 days of April.
Why might we use the tsurigama then? Because that is the season when the eastern wind (kochi) blows. At that time, when we hang the tsurigama, there is a faint breeze in the house which causes the kettle to slowly sway. With that swaying, the feelings of the host and guests that Spring is steadily coming closer meet.
Since the tsurigama suits the season when true feelings can crossover with the Spring breeze, it doesn’t matter when it is used if it has the nature of that season.