When you first go to start your garden, you will have to put a plant pot in your garden to grow the seed in. Some basic pots will be available to you at first. Some special edition ones come free, with special seasonal plants, and some are just the basic pots that are bouncing around in the Fairyland world.
Usually it doesn't matter what you plant your seeds in, but certain kinds of plants (like cacti, bonsai, and mushrooms) must be grown in a certain kind of pot. Some special edition or seasonal plants can only be planted as a set - IE, when you get a free plant, it comes in its own pot (see seasonal or special edition plant articles for examples).
But for certain plants - notably the Praecocia plants - FLORA (level 14), ROSA (Level 15) and TULIPA (Level 16) plants, the pot they are planted in matters very much! If you plant the seed in the right pot, it will grow into a precious gem. If you put it in the wrong pot (even if it was the right pot for another kind of Praecocia seed) it will just grow into an ugly, grey rock.
Some of the pots are easily mistaken for each other. Notable mixups are between the Coconut / Upturned Mushroom, Clay Pot / Golden Pot, and Old Bucket / Rusty Bucket. Refer to the picture at right to see the basic pots - or just click on the little icon of a pot in your menu bar (see pic).