NEW YORK -- Baby boomers with green thumbs helped lift gardening and lawn-care spending to a record $17.5 billion last year, up 23 percent from 1986, the National Gardening Association reported this week.

The gardening population also increased, with the addition of 1 million households, raising the total to 70 million of the nation's 89.5 million households.

The NGA report, based on the 1987-88 National Gardening Survey conducted by the Gallup Organization of Princeton, N.J., showed the average lawn and garden consumer spent $271 last year, compared with $196 in 1986 and $159 in 1985.

Men accounted for about $10.1 billion of gardening spending, up $2.7 billion from 1986; women accounted for about $7.3 billion, up $527 million.

Spending, up in all age groups, was heaviest in the 30-49 age bracket, which put out $8.6 billion, $2.3 billion more than in 1986.

"Trends revealed by the survey indicate many positive changes just over the past four years," Charles Scott, president of the National Gardening Association, a Burlington, Vt., nonprofit organization for gardeners.

"As demographers track life style and spending habits of America's baby boomers, they will note that lawn and garden participation and spending by this group continues to dominate the market and is on the increase," he said.

"We have seen more involvement by more households in a diverse number of gardening activities, actually creating some new gardening categories such as herb gardening and container gardening that didn't exist in quantifiable numbers until recently," Scott said.

"There have been changes in people's motivation for gardening. Landscaping has proven to increase real estate values, promoting an increase in the dollars invested.

"Vegetable gardening motivation has changed from the economics of saving money to having fresher tasting, more nutritious food," he said.

Scott, publisher of National Gardening magazine, reported these other highlights:

59 percent, 53 million households, do their own lawn and garden care, 1 million more than in 1986.

43 percent, 39 million households, grow flowers, the same as in 1986.

41 percent, 37 million households, have indoor houseplants, up 1 million over 1986.

33 percent, 29 million households, grow vegetables, down 2 million since 1986.

30 percent, 27 million households, use insect controls, down 2 million since 1986.

7 percent, 6 million households, do herb gardening, up 1 million over 1986.