Won, the traveling merchant, stays at Zack's house and open his booth. He sells different seeds from Vesta. To buy a seed, you just need to tell him. But, Won hates debt and credit!
Here is the seeds list:

Spring
Cabbage - 500 G. Harvest in 15 days.
Asparagus - 320 G. Grows in 9 days.

Summer
Pineapple - 1000 G. Harvest in 21 days, regrows in 5 days.
Water Melon - 480 G. Grows in 12 days, regrows in 4 days.

Fall
Green Pepper - 150 G. Harvest in 8 days, regrows in 2 days.
Peanut - 200 G. Grows in 7 days.

Winter
Broccoli - 150 G. Grows in 9 days, regrows in 2 days.