Laylarose: It's hard to come up with a rule of thumb for all plants. Some like to be crowded in a pot that's really too small for optimum plant growth, but it makes them bloom better. It's really the roots you're concerned with, anyway. Ask yourself does this plant have more/ less roots? Generally speaking tho, the larger your pot, the less often you have to water. Happy gardening ! :)
I have always stuffed my containers full of annuals when I've planted them; you can get away with more in a container than the spacing recommended when you plant them in the ground. Here are some really good links:
I use polymer crystals in my containers for water retention, but I have an acquaintance who's had great success lining the bottom of his containers with pieces of cut up sponge; the sponges absorb liquid when he waters while still allowing for drainage, and when the soil around them becomes dry, it absorbs the water from the sponges. He said he and his wife left their container plants unwatered for nearly a week this way with no problem.
Thanks so much! Have to go to dollar tree and buy some of those sponges. Such a good idea. Don't know if ya'll have a wal-mart near but they have 8 inch pots in white green and creamy color for .97 and they have drain bowl. Daughter works there so I get 10% discount.LOL and boy do I need it.