I do not use and do not grow fennel myself, but this year I am planning new garden to a novice friend who wants to plant fennel for bulbs. I am finding conflicting information about fennel: Most sites say - it is perennial. At the same time it is self-seeded as dill, but distance required between plants is 1 foot. Bulb is formed in cool weather, and harvested by cutting it from the long tap root, that stays in the ground. My question is - what happen to a perennial plant after that? Will the root die, or will it create a new crown like horseradish or dandelion? If yes, how long will it take, same season or next? If I want self-renewing patch of fennel, how would I achieve it?
Thanks in advance!
florence fennel (the bulbing one) is an annual. common fennel is a weedy perennial and does not bulb, you harvest the seeds in late fall. florence needs mild winters to become big enough, it is basically a mediterranean winter vegetable. I have tried it in MI for years, if you plant it in July it does not get big enough, if you plant it in June it bolts. so I only grow the perennial one now, and get the seeds.
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Thanks! I did have a feeling, that it is impossible to grow it here, just couldn’t find why 
. Thanks a lot again!
Make sure you get seeds for bulb fennel! They also sell leaf fennel, which will not bulb. I believe that is what you will commonly find sold retail as an herb.
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Thanks, I got that part. Looks like it will not grow here in zone 5.
Let me add that at the local farmer market there are occasionally small fennel bulbs on sale, well below 1/2 lb, so I am hardly the only one failing. A good bulb can weigh easily one lb, up to two, but it is a plant that will not take below 20F happily.
@ampersand and @glib, thanks again. May be it is possible, maybe it will fail to bulb, thing is, this is for a very novice gardener, with one 4x8 bed and few 1 sq foot containers. I don’t want to take her space away with something that is not exactly fitting the growing conditions here. She has a big lot, so I was thinking we can just plant it on a side as wild thing, something not to spend time on, that will renew itself as dill. Looks like it is not the case - I will skip on it, she will buy fennel until her skills and passion for gardening will make her to try! I will not maintain 2 gardens, I am just helping her to start
I start FF in peat pots in June/July. They are transplanted into my spent lettuce raised beds which are 80% horse manure. I water every 2-3 days and grow them under 30% shade cloth till mid Aug. Harvest just before frost in Oct. I regularly get 3-4" bulbs. They get chopped and frozen and used in stock and roasts. I use the hybrids.
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I see you in the same zone as me! So it is possible with proper care. I will let my friend know. When she is ready and have more garden space, she may do it.
Sufficient water and a loose, fertile soil will get you lots of fennel. Do use the hybrids as they grow faster. The seedlings are susceptible to damping off.
Galinas, I planted one ornamental (herb) fennel 6 years ago and even here in a mild zone7 it is far from being in the class of dandelion or horseradish. Here it seems to be a 2 or 3 year perrrenial tops it has naturalized some and there are a couple clumps around the yard, my guess is the chickens spread the seed and without cultivation and a bit of irrigation from me even those few clumps wouldn’t be there. The stems do well in soup perhaps not as good as the bulb but nice in minestrone. Fennel does have a deserved reputation as being attractive to all sorts of wasps (part of why I pamper it) if your friend is going to be squeamish about that I’d advise her not to plant it. If the wasps don’t put her off though and she likes it it doesn’t take much effort to encourage or eliminate so why not? Tom
Thanks, guys, I will let her know!