How To Grow Fennel

How To Grow Fennel

Fennel is easy to grow. They prefer full sun and a well drained soil. They will do best in rich soils.Water them during dry periods, once or twice per week. Add a general purpose fertilizer once or twice a season. While classified as a herb, Fennel is a popular European vegetable too. Native to Mediterranean region, the bulbous base and stalk is popular eaten raw like celery, cooked, or boiled. Closely related to Parsley, Fennel is popular in Italian and other Mediterranean recipes. Also called Florence Fennel or Finuccio, it is easy to grow and very hardy, lasting well after the first frost. With bright green, fern-like leaves and aromatic yellow flowers, this plant will grow three to four feet tall. Plant it in the back of the herb garden or in your vegetable garden. Foliage and seeds have an anise-like flavor.

Fennel Propagation

Fennel are grown from seed. Directly sow Fennel seeds into your garden as early in the season as the ground can be worked. Sow seeds early in the season and cover with 1/4" of soil. Space seedlings or thin plants to 10-12" apart, in rows 18-24 inches apart. Start a new planting in mid summer to harvest in the Autumn.

Sowing Fennel

Recommended Varieties: Rondo F1, Romanesco, Orion (Organic Variety).

Fennel can be started off indoors in mid May and sown until late June. Sowing in modular trays is recommended as fennel doesn't like root disturbance.

Sowing in Modular Trays

Use a seed compost which has a finer texture and lower nutrients than your standard multipurpose compost. We use a seed module tray with each section being approx 2 inches deep.

Here's what you do:

  • Fill the seed tray with compost and brush off any excess. When filling the tray rub the compost through your hands to break up any lumps. Give the tray a sharp bang on your table to settle.
  • With your fingers make small depressions in each cell about a fingernail or 1cm deep.
  • Sow 1 or 2 seeds per module. If 2 seeds germinate you will have to remove the weaker seedling.
  • Cover the seeds with another layer of compost then scrape across the top of the tray with a stick to remove excess.
  • Gently water your seeds. A good tip is to use a plastic bottle with small holes punched in the cap. This is less likely to wash the seed around than the heavy spray from a watering can.
  • Place your trays in a warm place at about 20 degrees C to germinate. They should be ready to plant out in about 4 weeks.

If the springtime weather is poor you may need to pot the modules on to 8cm pots and leave them in the tunnel or greenhouse. Planting is delayed by couple of weeks but you'll definitely get better plants.

Fennel Seedling Care

When growing seedlings indoors you be careful they don't get leggy, i.e. long spindly plants.

Leggy Seedlings

Seedlings become 'leggy' when they get too much heat and not enough light. If you are starting them off on a windowsill make sure they get as much daylight as possible. You can make a makeshift light box by placing a sheet of reflective tinfoil on the room side of the seedling tray. This will reflect daylight onto the darker side of the plant.

If the plants are on a heat bench or in a propagator and they are looking spindly, turn the heat down and try to give them as much light as possible.

If 2 fennel seedlings have germinated in any of your pots you need to remove the weaker one. Don't pull the seedling out as you'll damage the roots of the one you want to keep. Nip the unlucky one with your finger nail or cut with a scissors.

You are actually far better to under rather than over water your plants. This may sound odd but making the roots search for water helps to develop a better root system. It's a bit like keeping fit.
You do need to be careful, however, not to let the compost plug completely dry out or it will form a crust on top and won't absorb the moisture the next time you water. It will all depend on the weather of course but on a hot day you will need to water twice a day, if it's it's dull every 2 days will be fine

Hardening Off
Fennel plants should hardened off before planting in their final positions, especially earlier sowings.

Plants that have been raised indoors will need to get used to the outdoor temperature and conditions before they can be planted outside, this will take about a week to 10 days depending on the weather.

The best way is to use a cloche or mini greenhouse. You can leave the cloche off the plants on dry frost free days and replace at night. Gradually increase the time with the cloche removed until the end of the week when you leave it off day and night.
If the weather is mild you may not need the cloche, just move the plants outside for longer periods each day.

If you have started your seeds on a windowsill you will need to leave them in an unheated room for a day or two before moving outside to the cloche.

Planting out Fennel Seedlings

You can plant out your fennel seedlings 4 or 5 weeks after your sowing date providing the weather id good. Seedlings which have been potted on should be planted out 7 weeks after sowing.

Water your plants well an hour before planting. To plant your seedling make a hole in the soil the approximate size of the seedling 'plug'. You need to push the soil in around the roots firmly with your fingers to get good contact with the soil. Don't firm down on the top of the soil as this can compact it and prevent moisture getting down to the plants roots. Water the plants after planting but do not soak them. You are better to transplant on a dull day or in the evening to prevent the plants wilting on a hot, dry day.

Fennel Crop Care

Water well in dry spells to prevent the plants from bolting.

Keep vigilant, slugs like young fennel plants. Use an organic slug pellet or slug beer trap.

Carrot Root Fly
If carrot root fly is a major problem in your garden it can also affect fennel. An unlikely problem.

I know you're probably groaning seeing seeing a picture of a hoe but it you do it often it is pretty much effortless. In fact I bet you'll enjoy it. My favourite tool by a country mile is the oscillating hoe, it's an old fashioned tool that works beautifully.

Why Hoe? Weeds compete with your plants for water, nutrients and light.

Fungal disease can be a problem for some crops and weeds can contribute to this by cutting down the air circulation around your plants. Plants with good, clear space between them will be much healthier than congested crops.

Microbial activity
You will also find hoeing makes your crops grow better. This is because it breaks up the top layer of the soil and lets air and moisture circulate freely. The added moisture and air speeds up microbial activity which breaks down organic matter and releases nutrients to your plants roots. Hoeing does a lot more than clear weeds, believe me!


Your fennel will be ready when the bulbs are about 7cm or so across. Cut just below the bulb at ground level. Harvest leaves as at any time. Harvest flower heads after seeds have formed and the flower head has died. Extract seeds and dry them in a cool, dry location.

Harvest bulbs when they reach tennis ball size or bigger. Pull every other one out as needed to allow those remaining to grow even bigger.
Do not pull these plants up in advance of the first frost. They are very hardy and should continue to thrive and grow, even after a number of hard frosts.
Fennel doesn't keep very well especially with the leaves still attached. Remove the leaves and use to flavour soups, stews or stock.
If the leaves are left on the plant they will they will suck out the moisture and the bulb will become soft.