The simplest method is to buy a Conjuration Spellcraft from Tomes and Scrolls in Hogsmeade. It costs 1,000 coins to buy the potting table with the big pot, but it’s well worth it.
It’s not a crucial piece of equipment in the early stages of the game, but it will enable you to access every spell Professor Garlick gave you for her second task.
The shop also sells medium pots which you can buy.
After buying the table, return to your Room of Requirements and locate a place for it. Now that you see it, you can use any plant seed you have in it.
You should be able to plant and grow anything you want after resolving the pot size issue. This also means you can now cultivate any seeds that need a big pot unlike before.
You can match the aesthetics of your own personal area with the various colors and styles that can be equipped, much like the other stations.