They will bud fine in what you have them in. But if you put them in a bigger pot they will yeild more. The bigger the root structure the bigger a plant it can support. Basically the size of the plant is limited by the size of the root structure.
What they are talking about above is if your plant runs out of space to grow roots, and it still wants to grow them, it's roots will start turning back on themselves and get so dense that some areas don't dry out so can't get oxygen and the roots start to rot! Root rot! Ahhhhhh!
So, always make sure your plant has as much room to grow as it needs. An indoor plant that's only going to grow to 24-36 inches might only need 3 gallons. But if you want a 4 or 5 foot plant you'll want to make sure the plant can support that much vegetation.
If you can't find 10 gallon pots you can use two 5 gallon pots stacked on top of each other. You cut the bottom out of the one the plant is currently in and then set it on top of another pot you filled with soil. You can have the bucket tucked into the botton one a little or not. Up to you. Just make sure it's stable.