What is 'Checking?'

Above is a great illustration of good plant "balance" in a container. The plant has not outgrown it's container, and yet it is not too tiny either. This plants roots will likely outgrow this container in a few days. It would then be need to be planted in the garden or a larger pot to insure continued uninterrupted growth. When the growth is interrupted, by the container size, weather that is too cool, (either outside or in a garage) too warm, dried out too many times for too long, a process called 'checking' can occur. When a plant is 'checked' it seldom will grow again at the desired pace if at all. I once had a broccoli plant stay 6" all summer, yup - until frost. One day of wrong doing will not cause this (unless they froze) but a plant that for instance is allowed to dry out to near withering time after time. Or the plant that is subjected to temps below 50 night after night.

Think incidences x duration.

 Stress = 'checking.'

Overpotting is also a problem but for different reasons. Imagine a tiny transplant in this same container. Watering is the issue. There is not enough 'plant' to use up the water in that amount of soil, so the plant may just sit and rot. If you are skilled, you may be able to regulate with care the water levels. This is why it is recommended tomatoes get re-potted twice, in stages to insure continued growth. Checking can also be a problem at the garden center at the end of the season when the remaining plants are at rock bottom prices. How many times have they dried out and blown across the parking lot? Where the perennials grown in a climate close to ours? If their plants always look good during the season, then likely no problems. If they are always blowing across the lot....do you want them at any price?