A Fennel planted last summer has experienced a lot of growth and has grown from about 20'' to over 5 foot. I am concerned though,regarding the very faded appearance of the leaves on the lower half?
The foliage will die off in the autumn, and new growth will come from the base of the plant in spring. So you need to cut down the dead stalks each year otherwise you will end up with a thicket of them.
Fennel is quite demanding in its requirements and these are even more difficult to meet in containers ... it needs consistently damp soil ... if it dries out at all it will bolt and run to flower and seed rather than produce a lovely swollen base to the stems. It sounds as if this is what has happened to yours. 😢
Herb fennel doesn't produce a fat stem at the base and is used as a flavouring, either subtle from teh fronds or more strong from the seeds which are very good with fishy dishes and are used in some curry spice mixes.
Both versions are good hosts for swallow-tailed butterfly caterpillars which do no harm to the eating qualities of the plants.
"We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
I live in west central Scotland - not where that photo is...