How to get Hollow Knight Silksong Plasmium

Where is Silksong Plasmium? This strange elixir has some seriously powerful properties, but don't take our word for it. What initially seems like an innocuous quest item gives you access to one of the most powerful tools at Hornet's disposal, provided you complete the quest first.

You can only get Plasmium in Hollow Knight Silksong once you speak to Alchemist Zylotol in the Wormways. Use a Silksong Simple Key to gain access to this location on the Silksong map, then proceed to Zylotol's laboratory at the top of the area. Speak to him twice to accept the 'Alchemist's Assistant' side quest and receive the Needle Phial. This is a Silksong Tool, so use the bench to the far left of Zylotol to equip and use it before you head out.

All Silksong Plasmium locations

There are four Plasmium locations in the Wormways, and they're all in set locations with guaranteed spawns. Much like Silksong Pollips, you can tell when you're close to Plasmium by the blue vines that grow in its vicinity or the blue glow that emanates from the bud itself.

Once you reach a bud, you must use the Needle Phial to extract the Plasmium from inside - just hitting the buds with your Needle will temporarily destroy them. Charge the needle by holding down the Tool input (↓ + RB), then release to inject it.

Plasmium location #1

This Plasmium is in the central area of the Wormways. Head down from Zylotol's laboratory and take the first left. Avoid the worm as you drop down, then continue left and follow the path up, over, and down. The Plasmium is on the next right - be prepared for a worm to jump out behind you as you approach it.

Plasmium location #2

This Plasmium is in the western area of the Wormways. Head down from the first Plasmium location and drop down to the platform suspended over the spikes. Head right, then take the next path down that leads to another platform suspended over spikes. Dash through the burrowing worms then take the next path down.

Go right then proceed down and to the left until you reach a dark area of the Wormways. Take the path up and around then down. Land on the left-hand ledge halfway down this shaft and break the false wall. Follow the path around, avoiding more spikes and enemies, to reach the Plasmium on the ledge to the bottom right.

Plasmium location #3

This Plasmium is in the eastern area of the Wormways. From the second Plasmium location, retrace your steps out of this dark section area, then continue down and right towards Bonegrave. Take the right-hand path just above it that leads to a mossy cave and the final Plasmium.

Now you have all the Silksong Plasmium requested, return to Zylotol to complete the 'Alchemist's Assistant' quest and receive your reward. The Plasmium Phial is one of the best tools in Silksong, giving you an additional way to heal on top of the usual method provided by your silk. You just have to remember to return to Zylotol to refill it - don't forget to open the nearest Silksong fast travel point to save time.

Before you leave the Wormways, pick up the Silksong Mask Shard in this biome and pick up one of the best Silksong Crests from the Boneways while you're at it. We can even help you find Silksong Silver Bells if you're working on clearing out your quest log.