Takes a light frost. Start indoors 4 to 6 weeks before your last frost; plant out up to 2 weeks after your last frost; sow outdoors up to 2 weeks after your last frost; sow in fall 10 to 14 weeks before your first fall frost. First harvest 60 to 90 days from sowing.
Put in your ZIP code to see when to start, plant and harvest fennel where you live, from your own frost dates.
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From seed to harvest
SowSeed goes inWeek 0
SproutFirst shoots showWeek 1–2
True leavesFirst real leavesWeek 2–4
Thin or plant outGive each plant roomWeek 4–6
Leaf growthLeaves fill outWeek 5–8
HarvestReady to pickWeek 8–13
How to plant and grow
Grow a bulbing type
Choose Florence fennel, the kind that forms a swollen bulb at the base. Common herb fennel is grown for leaves and seed and does not bulb.
Sow in place
Fennel dislikes being moved, so direct sowing works best. Sow seed 1/4 inch deep after your last frost, once soil is 50 to 75 °F.
Or start a few indoors
Start seed in small pots 4 to 6 weeks before the last frost. Set plants out before they get rootbound, which can make them bolt.
Thin for bulbs
Thin seedlings to 4 to 12 inches apart in rows about 18 inches apart. Wider spacing leaves room for bigger bulbs.
Keep soil moist
Give 1 to 2 inches of water a week. Dry soil pushes plants to flower instead of bulbing. Mound soil around swelling bulbs to blanch them.
Aim for cool weather
Long, hot days make fennel bolt. A sowing in early to mid-summer matures in the cool days of fall, and plants take a light frost.
Harvest at tennis-ball size
Cut bulbs at about the size of a tennis ball, before a flower stalk forms. Most varieties need 60 to 90 days.
Common problems
BoltingGrowing problemNo spray helps
What you'll see: The plant sends up a flower stalk early, and the leaves turn small and bitter. Long days and heat set it off, and in bok choy and other cabbage-family greens so can a late frost or a week of nights below 50 °F.
Prevent
Sow in the cool, shorter days of spring and fall.
Sow small amounts every few weeks rather than all at once.
Choose varieties sold as slow to bolt.
Give afternoon shade in hot spells.
Organic options
Harvest as soon as a stalk starts. Let a few cilantro or dill plants flower for seed and for helpful insects.
Conventional options
None. No spray stops bolting.
Photo: “Aphids on Kale leaf” by Sanjay Acharya, CC BY-SA 4.0, via Wikimedia Commons (cropped). The cropped version is shared under the same licence.
AphidsPest
What you'll see: Clusters of small, soft-bodied green, black or gray insects on new shoots and under leaves. Leaves curl, and a sticky film may coat them.
Prevent
Check leaf undersides each week; a few aphids do little harm.
Pull nearby weeds, such as wild mustards, that feed aphids.
Grow flowers for lady beetles, lacewings and hover flies, and avoid broad sprays that kill them.
Organic options
Knock aphids off with a strong spray of water.
Insecticidal soap or horticultural oil on leaf undersides, repeated as the label allows.
Neem oil, or OMRI Listed pyrethrins (without piperonyl butoxide).
Conventional options
Malathion or permethrin, if the crop is on the label. These also kill the insects that eat aphids.
Bee caution: Don't spray open flowers. Spray in the late evening, when bees aren't flying.
Swallowtail caterpillarsPestSprays are rarely needed
What you'll see: Plump green caterpillars banded in black with yellow dots eat parsley, dill, fennel and parsnip leaves. They grow into black swallowtail butterflies.
Prevent
Plant extra parsley or dill to share.
Check plants in the morning.
Organic options
Hand-pick, or move caterpillars to a spare patch of dill or fennel.
Conventional options
Same as organic.
Photo: “Powdery mildew 9” by Dmitry Brant, CC BY-SA 4.0, via Wikimedia Commons (cropped). The cropped version is shared under the same licence.
Powdery mildewDisease
What you'll see: White, powdery patches on the tops of leaves and on stems. Leaves yellow and dry, and fruit may ripen poorly.
Prevent
Grow resistant varieties.
Give plants sun and space for air flow.
Remove badly infected leaves, and clear debris after harvest.
Organic options
Sulfur or potassium bicarbonate, from the first spots. Sulfur can burn some vine crops in heat, and never use it near an oil spray.
Neem oil. Look for OMRI Listed products.
Conventional options
Myclobutanil or propiconazole, if the crop is on the label.
Bee caution: Don't spray open flowers. Spray in the late evening, when bees aren't flying.
Root rotDiseaseNo spray helps
What you'll see: Plants yellow, wilt and die back even though the soil is wet. Roots are brown, soft and few, and bean seedlings may rot at the soil line.
Prevent
Plant in well-drained soil; grow raspberries on beds raised about a foot.
Do not overwater.
Plant beans and peas in a new spot each year, and sow them only once the soil has warmed.
Start with healthy plants, and do not move soil from a sick bed to a healthy one.
Organic options
Remove and dispose of dying plants and clear crop debris after harvest.
Conventional options
None. Fungicides have not proven effective in home gardens; drainage is the fix.
Read and follow the product label: it is the law. It sets the rate, the crops it is for, and the days between spraying and picking. Products registered vary by state; for organic growing, look for products allowed under the USDA National Organic Program (OMRI Listed). We name active ingredients, not brands or rates.
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Sow
Sprout
True leaves
Thin or plant out
Leaf growth
Harvest
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