Plant it to grow Foliage. You can't see the forest for this stuff.
Foliage Seed price in Growtopia: sells for about 15/WL, buyers pay about 20/WL (median of 30 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.
Recently sold at: MICAX, FOYED, RKUYJ, PANSE, URRNO