Herb
Fennel
Foeniculum vulgare · Apiaceae
Also called: Common fennel, Sweet fennel, Florence fennel (var. azoricum, the bulbing type)
Fennel (Foeniculum vulgare) is a moderate-water herb well suited to Tucson and the low desert. It thrives in full sun in cool months, with a fast growth rate. Expect yellow blooms late spring to summer.
Fennel at a glance
- Water use
- Moderate (established)
- Sun
- Full sun in cool months; benefits from afternoon shade as Tucson temperatures rise.
- Mature size
- Herb/seed fennel 3-6 ft tall, 1.5-3 ft wide; bulbing 'Florence' fennel about 2 ft tall.
- Growth rate
- Fast
- Bloom
- Yellow, Late spring to summer (yellow umbel flowers); seed follows.
- Cold hardiness
- Herb fennel is a frost-tolerant short-lived perennial in Tucson that can persist year to year; Florence (bulbing) fennel is grown as a cool-season annual and bolts in heat. Hard freezes can knock back top growth.
- Soil
- Well-drained soil amended with compost; tolerates alkaline desert soil; bulbing types want richer, evenly moist soil.
- Native range
- Mediterranean region; not native to the Sonoran Desert (naturalized/considered weedy/invasive in parts of the Western U.S.)
- Best used as
- Culinary herb (fronds, seed, and bulb for cooking), Butterfly host plant, Pollinator plant, Container or kitchen garden
- Wildlife
- Larval host for black swallowtail butterflies; flowers attract bees and beneficial insects.
- Toxicity
- Edible and non-toxic to humans; generally regarded as safe around pets. Note: can be invasive/weedy, so deadhead to limit reseeding.
How to grow Fennel in Tucson & the low desert
Watering
Water to keep soil evenly moist, 2-3x/week in mild weather; bulbing Florence fennel needs steady moisture to form tender bulbs. Established herb fennel is fairly drought-tolerant but produces best with regular water.
Fertilizer & nutrients
Light feeder; mix compost into the bed at planting. Florence fennel benefits from periodic balanced feeding to size up bulbs; herb fennel needs little supplemental fertilizer.
Pruning & care
Cut back flower stalks to prolong leaf production and prevent heavy self-seeding; harvest foliage and seed as needed. For Florence fennel, mound soil around the swelling bulb (blanching) for tenderness.
Notes
In Tucson, sow/plant in the COOL SEASON: Florence (bulbing) fennel September-October (fall) or January for a spring crop, since it bolts in heat. Herb/seed fennel can persist as a perennial with afternoon shade and summer water. Direct-sow when possible (taproot dislikes transplanting). Deadhead flowers to prevent it from naturalizing weedily. Do not plant near dill (cross-pollination/flavor concerns).
Sources: University of Arizona Cooperative Extension; Pima County Master Gardeners; Arizona-Sonora Desert Museum