Costa Rica: home of the F-1 (flower seeds, not bombers)

The soil is so rich here and the climate so perfect that the four-foot-high stumps of Poro trees stuck into the ground as fence posts take root and grow.

So it's no surprise that this land of the living fenceposts is also the home of the world's largest producer of F-1 hybrid flower seeds.

Linda Vista Ltd., a deceptively quaint-looking farm two miles outside Costa Rica's oldest and most colonial city, specializes in producing specific bedding plants - that is, the seeds of impatiens, geraniums, petunias, and snapdragons.

The 100-acre farm sits at a cool 4,800 feet in the shadow of Irazu Volcano and its chain-link fence entrance on an obscure red dirt road is its own best advertisement. Pink, white, and red impatiens spray the fence and gate. A fruit-laden orange tree droops heavily over the front office.

The Central Valley's climate and altitude are the reasons why the region is called the ''garden of the Americas.'' And Linda Vista production manager Fernando Vialta says they are the big factors behind the seed farm's productivity, which last year brought $3.4 million in sales in the United States , Europe, and Britain.

Linda Vista produces 80 percent of the world's impatiens seeds and 60 percent of the world's geranium seeds, he says.

''Just about everything here is done by hand,'' Mr. Vialta says, gesturing toward the farm's 45 greenhouses.

He points to a woman wearing a blue bandana and bending over a tray of flowering pink petunias. This, he says, is how ''petunia 12'' and ''petunia 59'' cross-pollinate - with an assist from greenhouse workers. The woman dips a sponge-tip metal wire into a small paper sheath containing a petunia male's pollen, then daubs it onto the ovules of the female plant.

About a month later, the product of fertilization will be precious F-1 hybrid flower seeds, the magic word in gardening and agriculture circles. (An F-1 hybrid is the first-generation cross between the ovule and pollen of selected parent plants.)

The farm's selective breeding guarantees the seeds will have the best characteristics of their parents. First-generation plants produced from F-1 hybrid seeds are heartier, larger, more colorful, and quicker to germinate.

They're also the most desired and most expensive seeds on the market: One pound of Linda Vista tomato seeds (more than 100,000 seeds) sells for $300 wholesale, while petunia seeds cost $5 a gram, and impatiens $6 a gram.

Linda Vista was founded in 1953 by Claude Hope, a retired US Army captain who first came to Costa Rica during World War II for a wartime development project.

Hope started in his now burgeoning business with a small plot and horse-drawn plows. Taking advantage of the climate, Costa Rica's abundant native plant species (impatiens grow wild here), and cheap labor, Linda Vista quickly grew into a giant.

''The literacy and education level of the employees has a lot to do with Linda Vista's success,'' says Alphonso Parada, an American and one of the company's four plant breeder/horticulturists. The business must in part thank its 1,000 employees for coming up with money-saving innovations at the farm, like using locally produced rice hulls to aerate soil mixes.

The hybrid-seed production business takes plenty of patience. The petunia seed an American backyard farmer plants in March to bloom in May takes about six months to produce.

After parent seedlings mature, plants are cross-pollinated by hand. About 30 days later, the flowers and seeds are removed, then dried and sorted by hand.

Seed weight determines quality. ''The lighter weight seeds are bad since their embryos have not full developed,'' explains seed manager Victor Manuel Rojas. In front of him are three women sitting at a table sifting black impatiens seeds no larger than the tip of a straight pin. They push a mound of seeds up a slanted tin tray, and when the lighter-weight ones don't fall readily , the women cast them away. Linda Vista seeds carry a 95 percent germination guarantee.

The sorted seeds are then put in muslin bags and air freighted to their market destinations - 14 square inches of seed valued at $25,000 a box. Rojas says the company sends about 30 shipments a month.