As a general rule Echinops do not grow well in pots. One need only browse plants in a garden centre or nursery to see that Echinops are often rather small, sickly looking plants when in pots. This is because Echinops are very deeply rooted plants, something which pots simply do not accommodate.
With this in mind, I generally prefer to plant Echinops as relatively small plants rather than attempting to grow them on, something which is often met with limited success. In terms of planting season, I have found that Echinops perform far better when planted in the Autumn – with Spring planted Echinops having a tendency to grow very little until the following year.
I have chalked this up to Echinops focussing their efforts initially on root growth over top growth, by planting them in the Autumn you therefore allow the plant sufficient time and moisture to generate a significant root system able to support tall and rapid growth the following Spring.