Boomseeds are small, light green, spiky seeds that, once the player collects them, appear in the upper-left corner of their screen. When dragged from the box, they will explode after a few seconds, terminating Phantoms, damaging Phantom Tubes, and destroying Phantom Webs and Phantom Sprouters in the area. They also appear as items in The Hive, The Great Escape, and Greely's Inferno. Large piles (such as the one shown) have an infinite amount of boomseeds, while trees will replenish the amount 5 times before they need to grow back, and small piles (that look like 3 boomseeds) will only replenish the player's boomseed count once, before disappearing. It will then reappear in several minutes.
To make Boomseeds, the player must combine Honey, Nectar, and Chomper Seeds in Cosmo's bowl. Next, they must gather specific vegetables from Cosmo's garden according to his directions. Then, they can harvest the seeds from Boomseed Trees.
- If a player has less than 2 boomseeds left, clicking on a boomseed in a tree will completely replenish it, costing only one seed off the tree.
- The player can only carry 3 boomseeds at a time.
- They were first introduced in the Meet Cosmo adventure.
- A den item tree with boomseeds on this tree is a prize for the Meet Cosmo adventure in Hard Mode.
- One single boomseed can terminate more than one Phantom at once.
- The Boomeseed looks very similar to Durian fruit and may be based on it.
- The Boomseeds inflict 100 damage points. This can be seen when dropping one on a Phantom Tube.
- If a player uses a small pile, all 3 boomseeds will disappear, regardless of how many the player had. This also happens with the trees (it can only be clicked 5 times, regardless of seed count).