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Dill is an umbellifer with a single fleshy taproot that goes straight down before the plant makes much top growth. By the time a seedling has its first feathery leaf, that root is already two or three inches (5 to 8 cm) long and pressed against the bottom of a cell tray. Lift it, and the root tip is either broken or bent, and a dill plant with a damaged tip almost always responds by flowering early on a stunted stem.
This is the single most common reason people report that their dill 'went straight to seed'. The plant was not stressed by heat at all; it was stressed by being moved. Sow the seed in its final position, thin ruthlessly, and you avoid the problem entirely.
If you must raise plants under cover because your spring is cold or your soil is heavy, use deep modules or three inch (7.5 cm) pots, sow three seeds per cell, and plant out within about three weeks of emergence with the rootball completely undisturbed. Never tease the roots apart, and never pot on.
A dill plant that flowers at six inches (15 cm) tall with a thin stem was almost certainly root-checked as a seedling. Nothing you do afterwards will make it bush out.
Depth, spacing and soil temperature
Dill seed is flat, light and needs only a quarter of an inch (5 mm) of soil over it. Sown deeper it germinates unevenly and the weaker seedlings never catch the leaders. It germinates from about 50F (10C) upwards, which is cool enough to sow well before most summer herbs, and it is fastest at 60 to 70F (15 to 21C), where you can expect seedlings in seven to ten days. In cold spring soil it can take three weeks, so do not give up and re-sow over the top.
| Factor | What to aim for | What goes wrong otherwise |
|---|---|---|
| Covering depth | A quarter inch (5 mm), firmed | Deeper sowing gives patchy, staggered emergence |
| Soil temperature | 55 to 70F (13 to 21C) | Below 50F (10C) seed sits for weeks and some rots |
| Final spacing for leaf | 4 to 6 inches (10 to 15 cm) | Crowded plants stretch, flop and bolt early |
| Final spacing for seed heads | 10 to 12 inches (25 to 30 cm) | Close spacing gives small, thin heads |
| Row spacing | 12 inches (30 cm) | Narrower rows make staking and cutting awkward |
| Days to emergence | 7 to 10 at 60F (15C) | Re-sowing too soon doubles up the stand |
Thin early, and thin twice
Dill seed is cheap and germination is usually good, so nearly everyone sows too thickly. A dense stand looks lush for two weeks and then collapses: the seedlings compete, stretch for light, make thin stems that cannot hold themselves up, and flower weeks early. Thinning is not optional maintenance, it is the main thing that decides whether you get leaf or a mouthful of flower stalk.
- First thin at the first true leaf As soon as the first feathery leaf appears beyond the two grassy seed leaves, thin to about two inches (5 cm) apart. Snip at soil level with scissors rather than pulling, because pulling drags the neighboring taproots sideways.
- Second thin two to three weeks later When the plants are four to six inches (10 to 15 cm) tall, thin again to the final spacing. These thinnings are full-flavored baby dill and are the best thing you will eat off the plant all season, so cut them into salad rather than composting them.
- Keep the strongest, not the tallest The tallest seedling in a crowded patch is usually the most stretched. Keep the one with the thickest stem base and the shortest gap between the seed leaves and the first true leaf.
Succession sowing beats one big sowing
Dill is a short-lived annual. From sowing, it gives you usable leaf for roughly six to eight weeks and then commits to flowering, and no amount of pinching stops it for long. The way to have leaf all season is to accept that and sow a new short row every two to three weeks from early spring until about eight weeks before your first autumn frost.
Each sowing needs only a foot or two (30 to 60 cm) of row. Sowing a whole bed at once gives you far more dill than any household uses in the fortnight before it all flowers together. Sowings made in the hottest part of summer will run to flower fastest, so sow those more thickly and treat them as a cutting patch rather than a standing crop.
In mild-winter areas an autumn sowing overwinters as a small rosette and gives you very early spring leaf followed by a large early seed head. Those overwintered plants are noticeably tougher and taller than spring-sown ones.
Let it self-seed, on your terms
Dill self-seeds freely, and in most gardens the volunteers are better plants than anything you sow deliberately. They germinate exactly when the soil conditions suit them, they were never transplanted, and their taproots are perfect. Leaving one or two plants to shed seed is the cheapest succession plan there is.
The catch is that they come up where they like, often in the middle of a path or through a carrot row. Decide on one bed or one corner as the dill area, let the heads shatter there, and cut every other head before the seed browns. Volunteers appearing outside that area are easy to hoe off at the grassy seed-leaf stage.
Write down where you let a head shed seed and the week the first volunteers appeared. In the second year that date tells you the earliest useful sowing window for your own soil far better than any packet does.