Planting fennel: seeds, location & companion plants


I studied horticultural sciences at university and in my free time you can find me in my own patch of land, growing anything with roots. I am particularly passionate about self-sufficiency and seasonal food.

Favourite fruit: quince, cornelian cherry and blueberries
Favourite vegetables: peas, tomatoes and garlic

No garden should be without fennel. As a vegetable, culinary herb, spice and medicinal plant, it brings so much to the table. Here are our top tips on growing fennel in the garden and in pots.

Bulb fennel plants with bushy feathery leaves
The ideal location for fennel is in full sun with deep, sandy loam soils [Photo: barmalini/]

Fennel (Foeniculum vulgare) is a Mediterranean plant that is now popular in our gardens too. This article tells you what you should bear in mind when sowing and planting fennel.

Planting fennel: where to plant the seedlings

Fennel grows best in sheltered, warm, sunny places with deep, moist, nutrient-rich, slightly chalky and sandy loam soils. Fennel can be cultivated in a raised bed or simply in a vegetable patch. It is also possible to grow fennel in pots on balconies and terraces, as long as the pots are large and high enough for the deep-rooted plant. For poor soils, be sure to enrich it with some mature compost in spring before planting your fennel to provide plenty of nutrients and improve the soil structure.

Young fennel plants with small roots and stalks
Fennel plants can be grown from March onwards in a warm, bright windowsill [Photo: fiore26/]

Planting fennel: how it works

Fennel is best grown as a main crop in the garden in successive rows. This allows a continuous harvest from July to October. If possible, keep a three to four year cultivation break between fennel and other umbellifer (Apiaceae) crops, such as carrots (Daucus carota), parsley (Petroselinum crispum) and chervil (Chaerophyllum bulbosum), to avoid the spread of plant diseases and soil fatigue. Fast-growing leafy vegetables such as spinach (Spinacia oleracea) or lettuce are good crops for growing before fennel.

Growing fennel from seed

Growing fennel begins on a sunny windowsill from the beginning of March. Direct sowing outdoors can only really be done from mid-April onwards, when the soil temperatures are well above 10 °C. But this is usually only done with herb fennel. Starting bulb fennel in pots and transplanting outdoors later will ensure stronger, healthier plants than with direct sowing. You can sow fennel seeds until August, extending the harvest time until October. Small pots filled with nutrient-poor seedling soil are ideal for sowing fennel seeds to begin with. Our Plantura Organic Herb & Seedling Compost is ideal for getting your plants started. This peat-free, low-salt compost has a good structure that promotes healthy root growth and stores moisture well to release to the plants when needed. Sow the individual fennel seeds about 1 to 2 cm deep in the soil and keep the soil moist. The seeds should germinate at temperatures between 18 and 22 °C after about 10 to 14 days.

Transplanting young fennel seedlings outdoors
From April onwards, the seedlings can be planted outdoors [Photo: Raffaella Galvani/]

Transplanting fennel

Once they reach a size of about five to eight centimetres, it is time to prick the seedlings out. From April, transplant seedlings into large pots with nutrient-rich potting soil or directly outdoors. When directly sowing herb fennel, make sure to thin out seedlings to a distance of 10 to 15 cm so that each young plant has enough space to grow. The plant spacing for bulb fennel, also called Florence fennel, is about 30 to 40 cm between individual plants as well as between rows.

If you want to grow bulb fennel in a pot, use a container with a volume of 3 to 5 litres per plant to accomodate its deep roots and thick bulb. Larger pots have the advantage of fitting more fennel plants and require less watering in summer. To create good drainage and prevent waterlogging, put a layer of approx. 5 cm of sand, gravel or expanded clay at the bottom of the pot. Then fill the pot with nutrient-rich potting soil such as our Plantura Organic Tomato & Vegetable Compost and place the fennel seedlings in the soil. Make sure that the plants do not sit deeper than they did in their previous pot and then press down around them. After planting, water the plants well.

Organic Tomato & Vegetable Compost, 40L
Organic Tomato & Vegetable Compost, 40L
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  • Perfect for tomatoes & other vegetables such as chillies, courgettes & more
  • For strong & healthy plant growth as well as an abundant vegetable harvest
  • Peat-free & organic soil: CO2-saving composition

When to plant fennel? Florence (bulb) fennel varieties can be planted outdoors as young plants between mid-April and mid-July. Some autumn fennel varieties will bolt and flower if planted too early, so it is important to sow them between July and August.

If you have enriched the soil with compost before planting, there is no need to apply fertiliser. However, when growing fennel in pots the soil and nutrient supply is limited. Therefore, the fennel plants can benefit immensely from an application of a plant-based fertiliser. Our Plantura Tomato Food is easy to apply by working into the surface of the soil where it will break down slowly over the course of several months. The balance of potassium in this fertiliser is ideal for fennel.

Tomato Food, 1.5kg
Tomato Food, 1.5kg
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  • Perfect for tomatoes, chillies, courgettes, cucumber & more
  • For healthy plants & an abundant tomato harvest
  • Long-lasting fertiliser that is free from animal products - child & pet friendly

Companion planting with fennel

It can be beneficial to plant fennel with certain plants to keep pests and diseases at bay and to avoid depleting the soil of nutrients.

Good companion plants for fennel include:

Bad neighbours include: 

  • Nightshade plants such as tomatoes (Solanum lycopersicum), peppers (Capsicum annuum) and potatoes (Solanum tuberosum)
  • Beans (Phaseolus vulgaris

Tip: Fennel itself should only be grown in the same place every four to five years.

In late summer, it is finally time to start harvesting your fennel. Learn everything you need to know about harvesting and storing fennel.