Container gardening is form of gardening in which a variety of plants, flowers and even vegetables are grown in pots rather than in the ground. It has exploded in popularity, according to the University of Illinois Extension website, because it allows plants to be grown in places previously thought impossible or unacceptable. Choosing the correct size pot is important because it can have a significant effect on plant growth and development, either supporting or hindering it.
A plant receives all of its nutrients from the soil. With less soil in a smaller pot, there are fewer nutrients available for the plant's root system. A pot that is too small also will constrict the plant's roots, not allowing them to spread out. If this happens, the plant's growth may slow down. One way to know if your plant needs a bigger pot is to look for roots poking out of the drainage holes in the bottom. A pot that is too small also will not be able to hold enough water to support the plant, and the plant can end up showing signs of drought sooner.
A pot that is too large for a plant can hold too much water in the soil, which can lead to mold growth, rot and root diseases. Too large of a plant pot also can make it difficult to keep the soil firmly packed around the plant's roots.
A pot should allow the plant's root system to spread out somewhat, and drain well. This means that the pot should not be soaked after it is watered, but that the water should drain out the bottom. The pot that a plant comes home in from a nursery typically is not appropriately sized. This pot is not meant for the long-term, but only to support the plant until it is either planted in the ground or repotted into an appropriately sized pot.
Choosing Pot Sizes
If an herb garden or several different flowers are placed in one pot, it should be at least 18 inches in diameter. Depth is sometimes more important than the pot's width. If flowers such as pansies are planted in window boxes, they should be at least 9 inches in depth. Most large vegetable plants, like tomatoes and beans, need at least a 5-gallon pot (see Resources).