You must first buy the seventh ($), eighth ($), and ninth ($20,) seed slots. As per the Plants vs zombies wiki: Extra Seed Slot ten - $80, (unavailable on iOS, Mobiles with Samsung bada OS, DS, and Android because. When will I be able to purchase this? One extra seed slot can be obtained in Pirate Seas, in a gate between Day 9 and Day 10 before the update or by completing Day 21 after the update. The. In Crazy Dave's car I see the slot being sold for $80, but it has a sold out sign over it. All together, it costs $, to get all 10 seed slots. seed slots plants vs zombies. .