Tomatoes and Chives
Beneficial Pair — Good Match
As with the other allium-scent claims on this site, the chemistry is real but untested for this specific application - no controlled trial we know of has measured a pest reduction on tomatoes from nearby chives. The perennial-versus-annual distinction below is a separate, more concrete practical fact rather than part of the evidence question.
Mechanism: Pest Masking (Scent Confusion)
Chives share the sulfur-compound scent chemistry of onions and garlic, both already paired with tomatoes elsewhere on this site for the same general scent-masking theory against egg-laying moths. What sets chives apart isn't the chemistry - it's that chives are a low, clumping perennial rather than a bulb crop replanted from scratch each year, which changes how this pairing fits into a bed you rotate tomatoes through season to season.
Chives, onions, and garlic all bring the same underlying sulfur-compound chemistry to a tomato pairing, but chives are the one that doesn't disappear at the end of the season - it's a hardy perennial that keeps growing in the same spot year after year.
A Permanent Plant in a Bed You Rotate
That permanence cuts both ways. On one hand, a chive clump established at a bed's edge means you're not replanting your scent-masking companion every spring the way you would with onions. On the other, most tomato-growing advice - including this site's - recommends rotating tomatoes to a different section of the garden each year to reduce soil-borne disease buildup, and a chive clump left in place doesn't move with the rotation. Plan on either accepting that the chives stay with the bed rather than the tomatoes, or propagating a new clump wherever tomatoes land next.
Spacing
Chives' compact 6-8 inch clumps tuck in at a tomato's base the same way onions or basil often do - their shallow, fibrous roots stay well clear of the deeper zone a tomato's own root system works.
Watch For
Because chives are perennial and tomatoes are typically rotated to a different bed each year to manage soil-borne disease risk, planting chives directly where this year's tomatoes are means next year's tomato bed - elsewhere in the rotation - won't have that same chive border unless you plant a fresh clump there too.
Frequently Asked Questions
Should I dig up and move my chives when I rotate tomatoes to a new bed?
You can divide an established clump and replant a portion in the new tomato bed if you want the pairing to follow the rotation - chives divide easily and transplant well, so this is a reasonable option if the scent-masking theory matters enough to you to bother.