[susan53]

Last spring is correct. Without the article "last" and "next" refer to the last/next whatever from the present moment. You only use the article if the reference point is not the present moment. So :

I'm going to Moscow next spring. (The reference point is the present moment, November 2010. So "next spring" = March or April 2011)


I went to New York in the autumn of 1980 and to California the next spring. (ie in 1981. The reference point is not the present moment but 1980)