At crocus, we have over 30 different sizes of pots that plants and trees are grown in. Here is a simple guide to the different options (and some nice pics of Mike our webmeister). 9cm 9cm is the size of pot commonly used for herbs. Herbaceous perennials are also sometimes sold in this size in early spring. 2 or 3 litre This is the normal size used for most shrubs and perennials. This is an excellent size: plants are small enough to establish quickly, but large enough to make an impact when first planted. 4 litre This size is commonly used for roses. The pots tend to be deeper than the 3 litre ones as roses like to put their roots down. 10 litre This is the size that many nurseries use for 'specimen' plants. These are plants that were grown in 3 litres last year, have been moved into these larger pots, and then grown on for another year. 50 litre This is the size for semi-mature shrubs and small trees. They are good for large gardens and instant, dramatic impact. 100 litre This is pretty much the size of a full grown shrub or small tree. Once planted it will look like it has been there for years. 500 litre These are truly massive plants. The pots are the size and weight of a Mini car. Usually these are the kind of huge, mature plants we use at Chelsea Flower Show.