Brussels Sprouts and Dill
Beneficial Pair — Good Match
This rests on the same integrated pest management research covering flowering umbellifers and brassica pests generally, which isn't narrowly specific to one brassica crop.
Mechanism: Pollinator / Beneficial-Insect Attraction
The same parasitic-wasp mechanism documented for broccoli and dill elsewhere on this site applies here - flowering dill's accessible umbel flowers draw small wasps that parasitize the caterpillar pests common to brassica crops, brussels sprouts included.
Brussels sprouts push this site's dill-and-parasitic-wasp strategy further than any other brassica pairing, simply because of how long the crop stays in the ground.
The Longest Season This Strategy Has to Cover
A brussels sprouts plant can take well over 100 days to mature, and many gardeners deliberately leave it in place through a light frost or two, since cold exposure is widely reported to sweeten the sprouts' flavor. That's a considerably longer window than broccoli's timeline, and a single flush of dill blooming mid-season won't cover it.
Staggering two or three dill sowings across the season, rather than one, is the practical way to keep flowering plants present from early sprout formation through a late fall or early winter harvest.
This also means the visible payoff from any single dill sowing is smaller here than with a shorter-season crop - a gardener checking only once mid-season might see the strategy working, then wrongly assume it's still covering the plant weeks later once that flush of blooms has faded and the sprouts are still forming.
Spacing
Follow the same spacing used for broccoli and dill, 12-18 inches, letting some dill mature to flower rather than harvesting all of it for the kitchen.
Watch For
Brussels sprouts often stay in the garden longer than any other brassica on this site, sometimes harvested after frost for improved flavor - succession-sow dill multiple times through the season to keep flowers available across that unusually extended window.
Frequently Asked Questions
Does letting dill go to seed near brussels sprouts cause a volunteer-dill problem the following spring?
It can - dill self-seeds readily once it flowers and finishes, and a bed that's hosted two or three staggered dill plantings by the time brussels sprouts are done can leave volunteer seedlings coming up there the next spring whether you planted dill again or not. Pull unwanted volunteers early, before they compete with whatever you're rotating into that bed next.
Does frost affect the dill plants themselves?
Yes - dill is considerably less cold-hardy than brussels sprouts, so late-season dill plantings may finish before the sprouts do, which is exactly why staggered sowings matter more here than for most other brassica-dill pairings.