I have finally gotten a shiny Ferroseed and I didn’t know it needed an egg move, so is there any other way to put Leech Seed on Ferroseed?
In Sword and Shield, if you have an empty slot in your Ferroseed's moveset, and another Ferroseed with Leech Seed, and leave them in the Daycare, the Ferroseed with Leech Seed will transfer Leech Seed to your shiny Ferroseed. This is a mechanic only able to be performed in Sword and Shield.
Source: Experience
Hope I helped!
Nope. Leech Seed is not a TR or TM. You must breed your Ferroseed for it to have Leech Seed.
I bred a Roselia with my Ferrothorn to pass on the leech seed. The move will always pass on so you need a male Roselia and female Ferrothorn for a Ferroseed with leech seed. Source
This is one of the best ways to breed it.
If you're playing Pokemon Sword and Shield only, there is a mechanic that allows you to give egg moves from one Pokemon to another.
Another new feature introduced in Sword and Shield is Egg Moves being passed through parents. If you have one parent who has the Egg Move, it can pass it on to the other if they are both left at the same Day Care Center.
The only pre-requisite is that the parent you want to learn the Egg Move needs to have an empty slot for each attack learned. Source