Answer: Both of these plants require two growing seasons to come into bloom and thus must be overwintered with their roots insulated somehow.
Hollyhocks are huge plants and need at large quantity of soil to thrive. Foxgloves often need staking and thus the pot must be large and heavy enough to handle that. Foxgloves will not bloom well if moisture stressed and in my experience do not do all that well in pots, either.
For container growing, it is often easier to stick with annuals that bloom all summer and do not need to be wintered over.
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