When to plant fennel – your questions answered

Know when to plant fennel and you can enjoy a continuous crop of this delicious plant to cook with – or as an architectural addition to your borders. 

Both a herb and vegetable, it is a little sensitive when it comes to having its roots disturbed, so you will need to know exactly how to grow fennel to ensure success with this versatile crop. 

When to plant fennel? The short answer is in spring, once the last frost has passed – but there are many more questions – which our experts clarify below.

When to plant fennel?

As with knowing when to plant vegetables in general, when you plant fennel depends on whether you are sowing indoors or out.

'Sow fennel seed indoors from March or outdoors where they are to grow once all frost has passed, which may be a better idea as they don't like their roots disturbed,' says H&G's garden expert Leigh Clapp, adding, ‘Sow seeds as soon as the soil can be worked early in the season. Incorporate plenty of organic matter into the soil.’

If you want to plant fennel in your kitchen garden that you've bought in containers, you can do so from late spring to early summer, being careful not to disturb the roots. Ensure that when you sow and plant fennel, you do so in a sunny part of the garden that has free-draining soil.

How late can you plant fennel?

You can plant fennel right through summer to August – you just need to ensure that, if you want to eat it, the harvest date will be before the first frosts.

How long before the fennel can be harvested?

If you sow fennel from seed, expect to harvest between 90 and 100 days later. 'To grow fennel bulbs takes around three months from sowing until the plant is ready to harvest, depending on the variety,' says Melanie Griffiths, editor of Period Living and gardening expert. When growing fennel as a herb, you can also begin to harvest the foliage within around 3 months from sowing.'

When to plant fennel for a constant harvest?

If you love to eat fennel regularly, it's worth knowing that you can plant fennel regularly to enjoy succession harvesting. 'Succession sow every few weeks until late summer for a continual supply of fennel,' advises Melanie Griffiths.

Can I plant fennel in winter?

You can plant fennel in winter if you live in one of the warmer zones; fennel is a tender plant, so sensitive to cold weather, but if your winters are warm, it should make it through the chillier seasons.

When to plant fennel next year?

Fennel is a perennial, so it will die back in fall, the re-grow again in spring. 'The herb fennel is a short-lived perennial, so will come back each year,' says Period Living editor and garden expert Melanie Griffiths. 'However, the plants will only last three to four years before you need to replace them.'

After three years, watch the activity of established fennel and if your plants show no signs of returning, plant new fennel again that spring.

Why is there fennel that I haven't planted in my borders?

Fennel will self-seed, so you may find it 'plants' itself in your borders without your involvement! 'Fennel seeds will happily scatter themselves as far as the wind – or birds – will carry them, so you may wonder why it appears when you haven't planted it. Or perhaps last year's fennel plants have self-seeded elsewhere in your yard?' suggests Homes & Gardens Editor in Chief Lucy Searle. 'If you don't want them to keep popping up uncontrolled, you will need to remove the flower heads, once they've died back, or seed heads, and dispose of them carefully.'