From www.ssa.gov
Eligibility requirements and benefit information
"When a worker files for retirement benefits, the worker's spouse may be eligible for a benefit based on the worker's earnings. Another requirement is that the spouse must be at least age 62 or have a qualifying child in her/his care. By a qualifying child, we mean a child who is under age 16 or who receives Social Security disability benefits.
The spousal benefit can be as much as half of the worker's "primary insurance amount," depending on the spouse's age at retirement. If the spouse begins receiving benefits before "normal (or full) retirement age," the spouse will receive a reduced benefit. However, if a spouse is caring for a qualifying child, the spousal benefit is not reduced.
If a spouse is eligible for a retirement benefit based on his or her own earnings, and if that benefit is higher than the spousal benefit, then we pay the retirement benefit. Otherwise we pay the spousal benefit."
So it looks like you must have filed for benefits- whether you begin collecting or not, then your spouse can get the greater of her benefit or half of yours after she reaches 62.
The SSA site is searchable and works pretty good.
Jim Ricks