Fennel Grow Guide

I don’t remember when we first started growing bulbing fennel (also called Florence Fennel or finocchio, but I’m guessing it was 2018. Like with everything else, I sparsely read up on it and then just dove in head-first mostly unschooled and completely curious.

I usually like to uncover cold tolerance, ideal soil temperatures for germination, and days to maturity to help me get my head around where in my seed-starting marathon I’d likely add a new crop.

Fennel has been growing for millennia as a prized culinary and medicinal herb. There are two types of fennel, leaf and bulbing, and I’m going to focus this post on bulbing - also known as florence fennel - as it’s the only type I’ve grown so far.

I definitely pushed the end of the season on these fennel, but it was for the garden tour. We will slice them thin and make a salad with them. I’m using these for a post-tour potluck celebration later this week.

What I love is the delicately beautiful foliage, its strong garden interest, the overall uniqueness, the anise-y flavor, and the challenges (opportunities) it provides in the kitchen during early summer and sometimes fall.

And possibly the best part? It’s one of our most disease-free vegetables in the garden. So the hardest part is getting those seedlings going, hardened off, and timing that planting right.

Varieties

I’ve only grown hybrid Florence fennel: Orazio is our tried and true and I recently picked up Solaris from High Mowing. They are both planted in the garden and while I see a slight difference in shape, they are all performing well — and I didn’t distinguish which ones were which so I really can’t tell you whether one is better than the other.

Culture

Fennel is one of those vegetables I wouldn’t really think of as a direct-seeded crop. I’m not sure why exactly, but I’ve always given it an indoor head start of 6 weeks or so. It’s quite similar to a carrot seedling in it’s early stages, with one main exception. It tends to sit a bit above the soil line when germinating, and the root collar is usually suspended in the air.

In researching this guide, I’ve learned that it is sensitive to root disturbance. Now if I had known this years ago, I may have started with direct seeding instead, but here we are with a tried and true indoor sowing and transplanting method.  

Seeding

Plant seeds 1/4” deep and covered; light is not required to aid germination. When seed starting use soil blocks or larger newspaper pots that you can easily and gently tear the paper back off them when transplanting.

A potted up Solaris seedling that was started on May 14, you can clearly see the root collar here, the line where the stem and root delineate. The root is that pale pink color and the stem is the white/pale green. I never plant them quite up to that line, but usually close when it comes time to transplanting. I don’t want to bury that line.

I always germinate fennel with the heat mat on, like almost all our veggies. If sowing directly in the ground, you’ll want soil temperatures to be above 55 for quick germination of seeds. Warmer soils will hasten germination, so with damp soils (overhead water daily until you see germination) you should see germination within the week.

Direct seed 1/4” deep, a cluster of 2-3 seeds for every 4-6” and thin to one plant per cluster after germination.

Plant Spacing

I usually give my fennel about 12” between plants because I like ot plant them in between sweet alyssym and snapdragons on my “end caps” of my main garden path.

If you will be growing them in their own bed in a more traditional way – like in rows – space them 4-6” apart with 18” row spacing, slightly more room than celery or carrots need.

How I interplant fennel it keeps it a bit cooler and thus less prone to bolting in early summer, though I fully admit the fennel I harvested last night for dinner was starting to bolt (we ate it anyway).

And speaking of interplanting, someone asked if it was okay to interplant it and again, this is where my ignorance serves me: I’ve never not interplanted fennel. I see it as a bonus vegetable, almost in the floral category with what it adds to the garden, so it’s always been interplanted and more of an ornamental vegetable than my standard work horse type crops like tomatoes and potatoes.

Irrigation

Florence fennel, like celery, forms crunchy stalks that are made of water. So yes, consistent and generous irrigation is key for this crop. Our garden beds receive an inch of water per week through our irrigation (calculated by the drip lines and how much time needed to release 1” of water).

But too much water can also be a bad thing. I’ve had springs where a beautiful fennel was harvested and had been rotting from the inside out from root rot or collar rot. I wondered at the time if perhaps I transplanted it too deep and the root collar was below ground and thus prone to rot.

Timing

Fennel is purported to grow better as the days grow shorter, meaning it’s a great fall crop. I’m trying to grow two fall successions this summer to test that theory. One is just about ready for transplanting and the next round I will seed with my fall iceberg lettuce soon (this week, mid-July).

Generally speaking, fennel should be ready about 2.5 - 3 months from when you seed it for bulbing fennel. This current harvest we’ve been having (for the past few weeks) was from our March 18 seeding that was transplanted in late April. We could have harvested these sooner, and I likely would have were it not for the garden tours. While our harvest is more like 3 months, they were sized up (the ideal size is about 4-6” wide) by mid-June. I was just holding onto their ornamental beauty and I even often let one go to seed too, just for fun.

So if you’re in my climate or warmer, sowing some fennel now for fall harvest is probably a great time. In addition to the indoor sowing, I am going to give direct seeding a try too, just to compare notes on whether I do need to indoor sow them for fall. I have a feeling direct seeding will work out just fine, though I will be strategic in selecting an area where I will simply thin to the right spacing rather than transplanting so I don’t disturb the roots.

Fertility 

Like so many wonderful foods, they are heavy feeders so they require soil with high organic matter and ample irrigation. I’d put it in the category with brassicas or celery, as they are both demanding in these areas too.

I transplant our normal 1/4 cup fertilizer in with each fennel seedling. And they grow in our compost-topped raised beds.

Harvesting

To harvest, cut the plant at the root collar. It’s a pretty tough root so perhaps pruning shears are the best tool for this job (this harvesting knife is better for squash, cabbage, broccoli, and lettuce).

You can harvest your fennel at any bulb size really. Sometimes I harvest them young if we have a hankering for a certain dish. You want to catch them before they bolt as like with other crops, this does change their flavor a bit. (Although we still eat and enjoy them even after they’ve started to sprout their flower stalk.)

Pest Pressure

Delightfully, fennel has very few pests and so it’s one of the easiest crops to grow in the garden, naturally pest-free.