I'll be honest, I didn't know this was a thing until literally just now which is why I'm sharing just in-case others are unaware.

If you are planting the spike and have your knife out, instead of stopping to equip your weapon and then restart the plant, you can just press 1 or 2 to 'ghost' swap to the weapon in that slot.
You will equip that weapon as soon as the spike has been planted.

Sorry if this is widely known already but I've only just come across this