The most important factors to look for when choosing celery roots are size, color, and firmness. A good celery root should be somewhere between 4 to 5 inches (about 10 to 12 cm) in diameter. You should also try to avoid any products that appear bruised or soft. Another feature to examine when choosing celery root is condition of the leaves, which should be green and appear fresh, if any are present. It is typically easier to find good quality celery roots during the cooler months, though that can depend on the local climate in your area.
Celery roots and celery stalks are not harvested from the same plants, though these vegetables do both come from the same species of plant. This species, which is known as apium graveolens, has two separate cultivars. One of the cultivars is harvested for the roots, and the other for the stalks and leaves. Another common name for celery root is celeriac, which helps to differentiate it from the common celery that is harvested for the stalks. Unlike most root vegetables, celery roots are relatively low in starch.
It is possible to grow celery roots throughout the year in areas that have temperate climates, though you should typically look for these vegetables during the cooler months in order to find the best produce. In climates where it gets warm in the summer, the best celery root will typically be found in the late fall, winter, and spring months. If your local climate is fairly cool all year, then you should also be able to find good celery roots in the summer months too.
One of the most important factors to consider when looking for a good celery root is size. The optimum size for this root vegetable is about the same as a softball, or no larger than 5 inches (12 cm) in diameter. Roots that are substantially smaller will not have fully developed yet, and larger ones will tend to be woody and tasteless. In addition to size, it is also a good idea to check the firmness and color of celery roots. They should be relatively firm, and free of bruises, though you should also avoid celery roots that are dried out.
Some celery roots are sold without any foliage, so you cannot always depend on the leaves when making a decision. If there are any leaves present though, they should be green and look fresh. Leaves that are dried out or slimy indicate that the celery root itself is likely to be sub par.