How to Grow Herb Fennel

Written by: - Growing Expert
Herb fennel

Unlike Florence, or bulb, fennel, which is grown for its bulbous stem, herb fennel is all about the leaf. Those feathery fronds add an aromatic, aniseed flavour to dishes, while the seeds can be saved for use in the kitchen too. With herb fennel being a hardy perennial that doesn’t require much care, this is a great plant to add into your vegetable garden.

Growing Herb Fennel: A Quick Snapshot

When to Sow – Mar-May

When to Plant – May-Jul

When to Harvest – Apr-Oct

Average Yield per Plant – 300g (leaf) or 100,000 seeds/year

Spacing – 35cm

Depth – 1cm

How to Grow Herb Fennel at Home

Herb fennel plants in garden

Although native to southern Europe, herb fennel is hardy enough to be successfully grown around the world. It can survive winter temperatures down to -17°C, and does well in the heat too. In regions that experience climatic extremes, herb fennel can be grown as an annual instead. So long as you’re able to meet its basic growing requirements, your herb fennel plants will happily thrive without the need for much intervention.

Growing Requirements for Herb Fennel

Herb fennel prefers sunny conditions. Ideally, at least six hours of sun a day. However, it’s also a plant that does just fine in shadier spots, making it handy for any darker corners of your garden where few other vegetables will grow.

In terms of soil, plant your herb fennel somewhere rich and well-draining. The richer your soil, the bushier your plants will be. However, herb fennel will still grow in poorer quality soils. While the plants may not be as tall or wide, their aroma will be just as strong.

Soil depth is important too, since fennel has a long taproot.

When choosing a site for your herb fennel, keep the plant’s height in mind. In perfect conditions, fennel plants can grow up to 2m tall. Plant it strategically, so that it doesn’t end up blocking light from your other crops.

How to Grow Herb Fennel from Seed

Herb fennel seedlings

Herb fennel doesn’t like to have its roots disturbed. For this reason, you’ll often end up with healthier plants if you direct sow them outside. Wait until a few weeks after your last spring frost before doing this. Although many will recommend sowing fennel seeds at around the same time as your last frost, cold conditions at sowing will cause your plants to bolt early.

If you want to get a head start on the growing season, or if you live in a colder climate, start your plants in modules indoors, before planting them out in late spring.

How to Sow Herb Fennel Seeds in Modules:

  • Fill modules with a multi-purpose compost
  • Water well, making sure that the drainage holes at the bottom of each module aren’t blocked
  • Make a shallow indentation in the centre of each module, about 1cm deep
  • Place one fennel seed into each indentation, and then cover over with soil
  • Lightly water again and then place your modules somewhere warm. The ideal germination temperature for fennel is 20°C

Your fennel seeds should germinate in about one to two weeks. Once they do, move them to a brighter spot and keep them well-watered until it’s time to plant them out.

How to Direct Sow Herb Fennel Seeds:

  • Prepare your growing area by thoroughly weeding it
  • Make shallow drills in the soil, just 1cm deep. Space each row 35cm apart
  • Sow your seeds thinly and then cover over with soil
  • If your soil was dry, give it some water

Once your seeds germinate, give them a week or so to grow before thinning them out. You’ll need to give each plant about 35cm of space.

How to Plant Herb Fennel Outside

Herb fennel young plants

Once the weather has warmed up at the end of spring, you can plant your herb fennel outside. Harden your seedlings off for 7-10 days before you do so, to help them adapt to outdoor conditions.

Ideally, try to plant your fennel out before the seedlings reach 15cm in height. Once they’re at this stage, they’ll have already produced a long taproot. Although they can still be transplanted, there’s a bigger chance that they won’t cope with this well. Even if they do still manage to establish, it will take much longer than if you were planting smaller seedlings.

Prepare your growing area and then dig small holes in the soil, just slightly larger than the root ball of each seedling. Gently remove each seedling from its module, taking care to disturb the roots as little as possible. Try to keep the root ball intact when doing this.

Place your plants into their new homes and cover their roots back over with soil. Firm the soil down around each plant and then give them some water.

How to Plant Herb Fennel in a Greenhouse

Due to its size, as well as the fact that it’s so hardy, most gardeners choose to grow herb fennel outside, rather than in a greenhouse.

That said, your greenhouse is still a useful asset when it comes to sowing fennel seeds. It’ll offer warmth and protection to your seedlings before they’re ready to be planted out.

If you plan on growing your herb fennel in pots, then starting them in a greenhouse will give you an earlier harvest. Leave your seedlings to thrive in the heat of your greenhouse in early spring, before moving your pots outside once the weather warms up.

How to Care for Herb Fennel

Fennel flowers

Herb fennel isn’t a demanding plant. So long as you provide the basics when it comes to care, it’ll do well on its own.

Watering Herb Fennel

Thanks to its long taproot, fennel is quite a drought-tolerant plant. It’s able to draw moisture up from deep within the soil, from areas that other plants can’t reach. So, while neglecting to water your fennel will likely not cause any serious problems, yields will be much better if you give your plants a consistent supply of water. Try to aim for about 2.5cm of water a week, which includes rainfall.

Feeding Herb Fennel

Herb fennel doesn’t need a fertiliser, but it’ll do better if given one. Use a slow-releasing nitrogen-rich mix, and apply this just once in the growing season, only after your plants have established. Fertilising your plants while they’re too young will put them at risk of damping off – a disease that causes young seedlings to collapse.

Weeding and Mulching Herb Fennel

Once your herb fennel plants get going, you won’t need to do much weeding around them. They’ll shoot up so quickly, far outcompeting any of their neighbouring weeds. That said, until they get to this stage, you’ll need to make sure that your young plants don’t end up smothered by weeds. Be careful when weeding around your fennel, so as not to disturb any roots.

Mulching your herb fennel plants is a great way to suppress weeds, while also giving your plants an extra boost. Use an organic mulch, since this will also feed your plants and soil as it breaks down.

Pruning Herb Fennel

While your herb fennel plants will do just fine without any pruning, cutting them back in early winter will help them to over-winter better. Wait until the foliage and stems have died back for the year, before snipping them away. It would then be a good idea to lay a mulch over the base of your plant, which will protect it over the winter.

Some gardeners choose to give their herb fennel plants an extra trim in early spring. This helps to encourage bushier plants.

If you’re growing herb fennel purely for its foliage or ornamental qualities, then snipping away any flowers before they have the chance to set seed would also be a good idea. This will prevent the plant from self-seeding all over your garden.

How to Harvest Herb Fennel

Fennel seeds on plant

If fennel leaves are what you’re after, then you can start to harvest them as soon as your plants are about 20cm tall. Simply snip off the leaves as and when needed, or cut a larger amount to preserve them for the winter. Whatever you do, never remove more than a third of the plant in one go.

If you’re growing fennel for its seeds, then try not to remove too much foliage during its growing season. The larger and bushier your fennel plants are, the more flowers, and therefore seeds, you’ll end up with.

To harvest fennel seeds, wait until the flowers have died back. You can harvest the seeds while they’re still green and then dry them yourself, or you can wait until they dry naturally on the plant. Once they do, they’ll turn brown, at which stage you can cut those stalks off. Do this over a paper bag to catch any seeds that fall. You can then easily separate them from the dried flower heads by lightly rubbing them in your hands.

It’s also worth noting that fennel flowers can be harvested while they’re still fresh. They have a subtle aniseed flavour to them and make a pretty garnish. Some also choose to harvest fresh flowers and then scrape off the pollen to use, which has an even more intense flavour than the leaves and stems.

How to Store Herb Fennel

Once picked, fennel leaves go limp very quickly. Ideally, use them as soon as possible after harvesting. Alternatively, cut off whole stalks and sit them in a jar of water (you’ll need to replace the water every day) to keep them fresh for a couple of weeks.

For long-term leaf storage, freezing or drying would be your best bet. When properly dried, the leaves will keep for a few years in an airtight container. Alternatively, chop up the leaves and stems and place them into ice cube trays. Once frozen, you can transfer your fennel cubes into an airtight bag or container. When stored in this way, they’ll last for about one year.

When it comes to the seeds, any green fennel seeds can be stored in the fridge for up to one week. Dried seeds have a much longer shelf-life – keep them in an airtight container and they’ll store for quite a few years.

If you’ve scraped off extra pollen, this can also be safely stored in an airtight container for a couple of years.

How to Prepare & Cook Herb Fennel

Chopped herb fennel

The bright, aniseed flavour of herb fennel lends itself well to so many dishes. The leaves and seeds are easy to use – once picked, there’s no much preparation needed. The leaves can simply be snipped directly onto a cooked dish as a garnish, while the seeds can be eaten raw or cooked.

If fennel isn’t a herb that you use very often in the kitchen, here are a few ideas to try:

  • Minced fennel leaves added to a green salad
  • Fennel stalks as a replacement for celery or lovage in stews and soups
  • Fennel leaves as a garnish for seafood
  • Ground fennel seeds added to just about anything – sauces, curries, pickles, bread, and even drinks
  • Fennel pollen added to a meat rub

It’s also worth trying a few fennel seeds on their own. They’re often eaten after a meal in many parts of the world because of how they prevent gas and help with digestion. You can either eat them as they are, or coat them in sugar first.

Common Herb Fennel Problems

Herb fennel isn’t prone to too many problems. Established plants release a strongly-scented essential oil that repels most pests, making herb fennel a good companion plant for other vegetables. That said, keep an eye out for the following issues:

  • Aphids – these garden pests will suck the sap from your herb fennel plants, causing them to wilt and distort. You can manually pick off small infestations, or use an organic spray to treat a larger infestation
  • Slugs – these pests are only really an issue with young seedlings, which they’ll decimate. Again, they can be picked off manually in the evenings, which is when they come out to feed. Alternatively, use a slug deterrent or set up some beer traps around your plants
  • Cercospora leaf blight – this disease is spread through infected seeds, or from water splashes or wind. Yellow spots will start to appear on the foliage. They’ll soon darken, and will be accompanied by a fluffy white growth underneath the leaves. A fungicide spray can help, but you’ll need to be careful about what you grow in this area in subsequent years

Popular Herb Fennel Varieties to Grow

Bronze fennel plants in garden

Unlike many of the other herbs out there, there are only two varieties of herb fennel to choose from:

  • Green Fennel
  • Bronze Fennel 

Both have very similar growing habits, with the main difference being the colour of the leaves. Green fennel is a classic, while bronze fennel produces beautiful copper-coloured leaves. Plant the two together for a stunning contrast.


While you may not harvest herb fennel quite as often as you do your other plants, the fact that it’s so easy to care for makes it worth having around. The plants also have a striking architectural quality to them that make them a focal point in any vegetable garden, while those feathery leaves provide a dramatic textural backdrop. Many gardeners grow herb fennel plants purely for their ornamental qualities, and it’s easy to see why!

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