Growing Dill: Why It Bolts, When to Resow and Who Eats It
Dill flowers as days lengthen, so sow again every couple of weeks for steady leaf. In North America, the striped caterpillars on it are often future swallowtails.
Sow a row of dill in spring and for a few weeks it’s all soft, feathery leaf. Then the days get long and warm, a thick stem shoots up, and the plant puts its energy into flowers and seed.
Because dill is wired to flower as days lengthen, steady harvests come from sowing it again and again, straight into the ground, and letting a few plants flower for seed, pickles and insects.
Why does dill bolt so fast?
Long days are its cue to flower, and heat and dry soil bring it forward. A 1939 paper in Botanical Gazette called dill “a very sensitive long day plant” in its title.
Garden guides name the stresses. The Royal Horticultural Society says that “in hot, dry conditions, dill tends to flower prematurely,” and Penn State Extension points to hot weather and dry spells. NC State Extension says consistent watering helps prevent bolting, and Utah State University adds overcrowding, recommending thinning and succession sowing.
Utah State also notes a trade-off. Leaf oil rises with longer days and higher temperatures, but heat above 35°C (converted from 95°F) cuts seed production.
Variety helps too. NC State lists ‘Fernleaf’ as the slowest to bolt, a dwarf for pots and small spaces, and the RHS rates ‘Domino’ and ‘Tetra’ as slow to bolt.
How often should you sow dill?
Every couple of weeks is a good middle path, though official advice runs from 10 days to 6 weeks.
| Source | Resowing advice |
|---|---|
| Penn State | Every 10 days while the weather is cool |
| UW-Madison | Every 10 to 14 days while the weather is cool |
| Illinois | Every two weeks through the growing season |
| NC State | Plant “every 2 or 4 weeks” for fresh use |
| Utah State | Every 4 to 6 weeks for a continuous leaf supply |
| RHS | Small batches every few weeks, mid-spring to midsummer |
The RHS explains the logic. Leaves are ready about six weeks after sowing, and the plant stays leafy “for several weeks until it starts to flower.” Each sowing gives a short window, so the shorter the gap between sowings, the more those windows overlap.
The two shortest intervals both come with “while the weather is cool,” and Illinois notes that plants “decline soon after they start to flower.” Utah State, with the longest gap, puts harvest at 6 to 8 weeks after sowing and says flavour “peaks once flowering starts,” so it treats each sowing as a longer crop.
Every source recommends repeat sowings. Illinois starts one to two weeks before the last frost, and UW-Madison adds late-summer sowings for an autumn crop, since dill tolerates light frost.
In hot climates, the cooler months suit it better. For Florida, UF/IFAS says dill is “best planted by seed, September through December,” though spring works too. That is autumn into early winter there, and our reading is that the same cool season suits other hot, frost-free places such as Brisbane, where that means roughly March to June.
Why sow dill where it will grow?
Because its long taproot resents being moved. NC State calls dill “a poor candidate for transplant” for that reason.
The RHS sows into a shallow row about 1 cm deep, with rows 30 cm apart, then thins to about 20 cm. In a pot, use one at least 30 cm deep and wide and pick a compact variety. If you start seeds indoors, plant out about four weeks after sowing, “before they form long tap roots.” The RHS adds that dill can grow on a sunny windowsill year-round, though plants are bushier in brighter months, and our windowsill herbs guide covers the light and drainage that make that work.
Leaves, flowers or seed for pickles?
All three are edible, and pickles can use any of them. Penn State says the seeds are “the primary flavoring in dill pickles.” It recommends ‘Mammoth’ for pickling and ‘Fernleaf’ for its leaves, and UF/IFAS names ‘Long Island Mammoth’ as the best performer in Florida. The RHS uses the flowers in pickles too, and Utah State suggests the whole plant.
For leaves, start picking about six weeks after sowing and keep at least a third of the plant, as the RHS advises. Regular picking delays flowering, and so does cutting off flower stems as they form. Use leaves fresh, because UW-Madison notes the flavour “rapidly declines when dried.”
For seed, the sources differ on the moment. The RHS harvests when the seeds turn brown and Utah State when the flower heads do. UW-Madison cuts heads once the seeds are fully developed but before they brown, because ripe seed shatters, and Illinois says roughly two to three weeks after the flowers open. Each of them mentions a paper bag, which catches falling seed and takes the pressure off getting the day exactly right.
If you skip the harvest, dill sows itself. The RHS says seed left on spent heads will “drop and germinate to provide new plants,” and Utah State warns it “can become weedy.” Penn State and UW-Madison suggest deadheading if you’d rather it didn’t.
Who is eating my dill?
In much of North America, especially east of the Rockies, it may be a future black swallowtail. UW-Madison Extension says this butterfly ranges from southern Canada to northern South America and is most common east of the Rocky Mountains. Its caterpillars feed on the carrot family, with dill, parsley and fennel common backyard hosts. Young caterpillars are black and spiny, and older ones turn green with black bands and yellow spots.
UW-Madison says they can be a pest in backyard gardens, but are usually “not numerous enough to present a real problem.” Handpicking works if needed, and caterpillars can be moved to suitable host plants outside the garden. Insecticides are “rarely justified,” the same page adds.
Does dill bring beneficial insects?
The flowers draw a crowd, and one field trial backs that up for hoverflies, which the researchers studied as aphid predators. NC State lists bees, wasps and hover flies among dill’s visitors. A two-season extension trial in New Hampshire found that alyssum, buckwheat, cilantro and dill had more hoverflies than calendula, phacelia and fennel.
The report is careful about the next step. “Additional work is needed,” it says, to show whether those hoverflies actually control crop pests. So flowering dill is a good bet for insect life, with the pest-control payoff still being tested.
What this means for you
- Resow every couple of weeks from just before your last frost to midsummer, or through the cooler months in a hot, frost-free climate.
- Sow direct, because dill’s taproot dislikes being moved.
- Water through dry spells and thin seedlings to slow bolting, and grow ‘Fernleaf’ if you mainly want leaves.
- Let one sowing flower for seed, pickles, hoverflies and, in North America, swallowtails.
- Bag the seed heads so ripe seed drops into the bag, or deadhead if you don’t want self-sown seedlings.
Do you resow dill through the season, or let one patch go to seed and come back on its own? Hit reply and tell us.
How we made this: AI tools helped us research and draft this post. We checked every figure, quote and link against its original source before publishing. Figures are as of 8 November 2026.
Grown with intention by Dynamic Nexus Garden.