Agriculture Reference
In-Depth Information
The thickened bulb elongates as Florence fennel bolts.
Italian heirloom varieties are different: if they are planted too early, they will bolt very quickly, so
they should be sown only in mid to late summer, whether for vegetables or for seed. Keep these frost-
free through the winter, in pots if necessary. Where winters are mild, overwintering outdoors is a pos-
sibility, as fennel can handle light frost. Harvest the bulb for eating in autumn. In the spring, small sec-
ondary bulbs develop, which will then bolt, blossom, and go to seed. Florence fennel can be continu-
ally harvested for three to four years in mild climates
Sweet fennel
is a perennial, hardy to zone 4. It can be sown in the spring, produces no bulb, flowers,
and goes to seed the first year (although the seed harvest the following year will yield higher). Sweet
fennel ranges in color from green to reddish bronze.
Bulbs and bolting
Many bolt-resistant varieties have been bred over the last 40 years. The Swiss research institute
Wädenswil made a breakthrough in fennel breeding with their 'Zefa Fino', introduced in 1979.
This variety was bred from the only two (!) fennel plants not to bolt in a large fennel planting; it
is still available from conventional and organic seed companies and traders. But note that bulb
development is not just a matter of breeding: weather (drought or heat stress), age, and size of
the seedling when planted are also factors.
SELECTION CHARACTERISTICS
The most important selection criterion for Florence fennel is bolt res-
istance: the later it bolts, the more time it has to develop its bulb. Other selection criteria:
• well-formed, round bulb
• consistent, uniform leaf formation
• light-colored bulb
• lack of stringiness of leaf sheaths and stems (easier to select for when growing as a biennial, as the
bulb can be harvested in the first year; avoid cutting too deeply into bulb)
Selection criteria for sweet fennel:
• stability (especially for large-scale production)
• synchronous ripening of seed
• resistance to dropping seed
• seed size, yield, and aroma
DISEASES AND PESTS
Fennel is loved by caterpillars of the Old World swallowtail butterfly (which,
despite its name, is also found in North America). The minimal damage done to fennel crops is fortu-
nately far outweighed by the joy of seeing these beautiful, rare insects.
