Fennel grows as a weed in Seattle, though if you’re looking for those luscious giant bulbs you see in the grocery store sometimes, you’re going to be disappointed. Our fennel is almost exclusively Foeniculum vulgare vulgare, which has long deep taproots and nothing bulbous, as I discovered when I eagerly dug up a fennel plant in my yard a few years ago. The bulb fennel is Foeniculum vulgare vulgare, variant azoricum. (1)
According to the American Herb Society, fennel is related to cumin, anise, dill, and caraway. (1) It looks extremely similar to dill, which you may also find growing in gardens around Seattle, so check for the familiar licorice smell before picking any.
The American Herb Society says fennel grows to just under 6 feet; the fennel in my yard has exceeded 8 feet some years.
If you’re looking for the leaves of fennel to use as a garnish, an herb in cooking, or a salad green, you can harvest these as soon as they come up, starting in early-to-mid spring. Avoid leaves (also called fronds) that are turning brown or yellow.
The major produce of non-bulb fennel, however, is seeds. To avoid massive new fennel crops in the next year, you need to harvest the seeds or remove the plants before the seeds fall too profusely.
I use scissors to cut the seed-producing clusters off each fennel stalk into a large bowl. Then I rub the clusters between my hands to agitate the seeds off the stems. I’ve managed to get over a cup of fennel seeds from one year’s harvest of 20-25 fennel stalks, growing in 5 or 6 clusters, more than anyone can use in a year unless they REALLY enjoy making their own body care products, tea, sausage or spaghetti sauce.
I strongly recommend NOT growing your own fennel, as it is adept at spreading itself around your yard and quickly grows deep roots that are extremely difficult to remove in their entirety. They will grow new plants even from just a small root piece.
Look for fennel plants in overgrown areas along roadsides, or in your neighbors’ yards.