Fatalistic Fennel?

My daughter wanted fennel seeds, so last year I planted fennel in a couple of my raised beds. I looked up how to grow it, companion plants and planted it. The tomato, squash, zinnia and cosmos germinated and grew very well. This year I have a tomato growing in that raised bed, and it seems to be growing as well as the other tomatoes in different beds.
I keep seeing fennel keeps other plants from growing, and even continues after the fennel has been removed. So far this is not my experience, but I keep seeing it and I'm a little worried.
Have you grown fennel? Did it have a negative affect on the surrounding plants, or soil?

I have Fennel planted in some of my orchard areas, but not in my vegetable garden.
I haven't noticed it preventing the growth of other plants in the orchard, except for taking up a lot of room and crowding out other plants when it gets big.  I have only just now read about its supposed allelopathic affect on certain types of vegetables.  The reason I don't have it in my garden is because it makes lots of seeds and volunteer plants come up readily making it weedy in my climate.
 

It grows wild here.

I've never noticed that it causes problems other than attempting to shade stuff out, but so far it hasn't invaded the veggie beds.

It's attempting to out-compete the prickly pears and the peruvian apple cactus though!

My daughter wants the seeds, so maybe when it looks like it's almost ready we should tie paper bags around the stem.
It's really growing fast now. It definitely shading the tomato to the east of it. So far the tomato seems to be growing well.  I don't know How long it will take the seeds to mature. If they don't mature soon I may have to tie them back a bit.
Thanks for your comments. I always trust the people on Permies a lot more than I believe in the info I get from the Internet.  Thanks

The allelopathy thing with fennel is real but seems to vary a lot by soil and conditions. I've had it growing near tomatoes without obvious issues too. The bigger problem in my experience is just the shading and root competition as it gets big. Paper bags over the seed heads is a good call, fennel self-seeds aggressively if you let it go.

I grow a lot of fennel, I have some that has been cut and came back now three years.  (North Central Texas)

It is right in my garden next to cukes, squash, egg plant, peppers, etc.  I have never seen any of my plants do worse next to fennel than away from it.  May be some things do but nothing common in a southern garden for me ever has.  None of my winter cover crops seem to be bothered by it either.

Thanks so much Jack that's very helpful.
This is the reason I love Permies. You can find a lot of interesting information on YouTube and the Internet, but it's difficult to know what is real in a real life situation, and what is false, or maybe technically it's true, but very dependent on the situation etc. With Permies it's a lot of smart people who are trying to do the best they can, and enjoy sharing what they know.
You are all awesome, Thanks.

Years ago I grew fennel from seed my brother gave me from plants growing ferally in Los Angeles. Not only did it survive in my West Virginia garden through a few years of (zone 6) winters, but I broke a couple of shovels trying to dig it out to move it. Too much damage to move, and I've never had such success with it since. I'm trying again and have a few seedlings in a garden bed now, figuring that's my best shot in getting it to germinate and survive, and I tried googling to see what the wisdom is on whether it's allellopathic or not. But I can tell you that the reason I dug that big healthy plat, that gave me a quart of seed every year, is because I noticed  other plants not doing well in the same bed. The one I specifically remember was peppers. Of course, you never know with a single trial whether what you observe is due to confounds, like different treatment of the soil, or being in the pathway of water moving underground, or maybe it was the shade. I've never seen it self-seeding, but that's probably because I'm growing it for the seed so I snip off seedheads as they ripen.

This is something that I have looked into before, and found a fairly definitive explanation.
Fennel, like many other plants in the parsley/carrot family, originated in summer-dry climates. In order to prevent the seeds from sprouting when there is not enough water for the plants to get well-established before the soil dries, their seeds are coated with natural germination inhibitors. Ever wonder why carrots and parsnips take so long to germinate? It's because the inhibitors must be washed off or biodegraded before the seed can sprout. If you soak and rinse them, they sprout much faster. In germination testing, seed companies routinely soak these seeds before trying to sprout them. In nature, the equivalent of soaking and rinsing is heavy rainfall or seasonal flooding.

Planting a few fennel seeds has little or no effect on neighboring plants. Nor does the presence of the plant itself poison other plants nearby (unlike black walnuts or wormwood, which both secrete poisons from their roots and foliage.) However, unlike carrots and parsnips, fennel is often grown to full maturity and allowed to set seed, which it does prolifically. It also can be perennial in mild climates, and turn into large plants that produce thousands of seeds year after year in the same location. A shower of fennel seeds can leach enough inhibitors into the soil to produce an effect on the germination of crops planted nearby.

You can remove the flower stalks as they start to form (and use them while soft and immature as a vegetable, as is done in Italy) or you can clip the seedheads before the seeds start to fall. Or you can grow fennel among other perennials, since existing plants are unlikely to be affected. I don't know about transplanting crop seedlings into soil where lots of fennel seed has fallen. I doubt that it would do more than slow them slightly; that's a topic for experiment. But as long as you realize that the culprit is a chemical that's found on the surface of the seeds, that the seeds need to be in the soil in fairly large quantities to have an effect, and that the poison is water-soluble, you have the tools to cope with it.

Interestingly, grasses (and other monocots like onions and lilies) tend to be immune to the inhibiting effect of this type of compound. So in climates like mine where fennel is an invasive weed along the roadside, you will see grasses around it, but not most wildflowers, which like many other broadleaf plants, are more sensitive to germination-inhibiting compounds. (Grasses and onions are even immune to juglone, and can grow directly under black walnut trees.)

Thank you Janie, now I can just leave my fennel where it is, in an improved garden bed where it has the best chance, without worrying about its effect on the flowers and peas and cumin I have near it.

Wow Jamie thank you so much. I didn't realize fennel was a perineal, I really dropped the ball when looking into growing fennel.  You have really cleared upa lot of my confusion.  My daughter wants the seeds, so maybe it's good it's a perineal. The only real down side is it's in a small 4' X 4' bed, and it takes up 3/4 of the bed.  once it's done producing seeds, I may have to trim it, or use some chicken wire to make a little more space.  Maybe I could grow melon by it. It can help keep the soil moist and the melon can climb out of the bed to gather the sun it needs.
Thanks

I have Italian large bulbed fennel, and a smaller amount of bronze fennel, all over our garden and food forest. It self seeds prolifically, which I am ok with because it is a great biomass producer on our difficult serpentine bedrock based soils, it’s foliage makes pesto on par with basil, and the flowers support dozens of pollinator and pest predator insect species. I have not notices it being allelopathic beyond being prolific. I have even seen benefits to seedlings and transplanted starts with its dappled shade, especially when chopped and dropped strategically. It also seems to be a snail shelter plant, making it a place to harvest chicken treats. That snails seem to live in it without eating it was said by Bill Mollison to be an indicator of a fire resistant plant. I think fennel is one of the most under-appreciated volunteers (my preferred nomenclature for “weeds”).

I could be wrong, but I think the seed co. I bought my fennel seeds from said that most fennel is an annual, but it's the bronze fennel that's perennial. That's what I bought. Of course all varieties self seed heavily, so there's that. My original plant is a beautiful plant, growing five or six feet tall and almost as broad. That did change my original plans for my "herb bed".

Like cilantro, I end up with at least a gallon bag of seeds, which are not only good in cooking (a little goes a long way), but great for sharing.

I've also had luck with just stabbing a spade straight down into the base to get roots to share, much as one would do in dividing other perennials. Ironically, the volunteers that came from seed seem to sink their root deep before much top growth, so are harder to get out. If they are in an inconvenient spot, I just chop them off knowing I'll have to do it again. Heavy mulch helps.
I have not noticed alliopathic symptoms. They seem happy with cilantro, tomatoes, and hollyhocks ~ three other reliable self seeders. They are spreading though, so I will keep an eye on my spinach and lettuces.

Whether fennel is perennial for you depends on location, and on the strain. Varieties that are bred for the large edible stem base ("bulb") are more annual, though some older heirlooms have perennializing tendencies https://www.quailseeds.com/store/p553/Selma_Fino_Fennel.html More might be found to survive the winter if you can master the trick of where to cut when you harvest the bulbing types. Too low and the crown is killed, too high and the "bulb" falls apart. Harvesting stem-by-stem would give the plant a chance to show whether it can overwinter or not.

Usually the reason you see bronze fennel listed as a perennial and the others as annuals is that they are bulbing types--it's the non-bulbing, wilder plant that is perennial, whether it's tinted bronze or green. It dies back to the root and re-sprouts in spring in my zone. I suspect that the determining factor in whether it survives the winter is whether the ground freezes or not, but that's conjecture.

Great thread!
I was at at an Indian grocery store buying dill seeds and considered buying fennel seeds.
I held off because of the potential allopathy.
But now I'm a little disappointed the allopathy doesn't affect grass,I was hoping for a perfect companion for tree seedlings.

I hate slugs and snails, but my lizard friends like them.
Being able to use the greens in pesto seals the deal for me, I will be spreading this plant into my yarden, which already has mints, and other wildish forage.

I wanted to grow it  like  a 'hedge' to shade the grass out which is invading. I find it hard to germinate, but had tons of seeds to play with and have discovered that dumping them in my multilayered sprouting device works very well. Probably as Jen said above the rinsing effect washes off those seed inhibitors.
Also they don't like to be transplanted and grow quite slow. So start them early in the year indoors and get them out of the pot carefully. I found they need help against grass getting taller or they get easily lost in it and then it's over for them.
Don't worry about ripping leaves off to make some space for neighboring plants they are strong and easily grow back.