Tomatoes and Borage
Beneficial Pair — Good Match
The pollinator-draw mechanism is well documented for borage in general polyculture and pollinator-garden research, and the logic connecting more bumblebee visits to better tomato buzz-pollination is sound. What's missing is a trial isolating borage specifically and measuring an actual yield increase in nearby tomatoes, which is why this stays mixed rather than evidence-backed. The hornworm-repellent claim has essentially no controlled support behind it.
Mechanism: Pollinator / Beneficial-Insect Attraction
Borage produces an unusually high volume of nectar and refills its flowers quickly, which makes it one of the most reliable bee magnets a vegetable gardener can plant, and bumblebees in particular are drawn to it in large numbers. Tomato flowers need buzz pollination - a rapid vibration that only bumblebees and a few other native bees can produce - to release pollen efficiently, so more bumblebee traffic in the bed is a genuinely plausible route to better fruit set. Borage is also separately reputed to repel tomato hornworm through its strong scent, though that claim rests on much thinner ground than the pollinator effect.
Borage is one of the few companion plants where the core claim - that it draws in large numbers of pollinators - isn't in dispute. What's less settled is how directly that translates into more or bigger tomatoes.
A Genuine Bumblebee Magnet
Borage flowers refill their nectar within minutes of being emptied, which is unusual and makes the plant extraordinarily attractive to foraging bees, especially bumblebees, which will often work a stand of borage far more intensively than most nearby vegetable flowers. Tomatoes rely on buzz pollination, where a bee grips the flower and vibrates its flight muscles at a specific frequency to shake pollen loose - honeybees mostly can't do this, but bumblebees can, and they're the main wild pollinator responsible for it in most home gardens. More bumblebee traffic in the immediate area from a nearby stand of borage is a genuinely reasonable route to more visits, and more visits, to tomato flowers.
Where the Evidence Runs Out
The gap is between "borage draws bumblebees" and "borage measurably increases tomato yield." Tomatoes are largely self-fertile and set fruit through wind and their own flower movement even without any pollinator visits at all, so the yield benefit from extra bee traffic, while plausible, is harder to isolate and hasn't been demonstrated in a controlled comparison specific to this pairing. The separate claim that borage's fuzzy leaves or scent repel tomato hornworm is even weaker - it's repeated often but doesn't have documented support behind it, and hornworm control is better handled by hand-picking or a targeted biological control like parasitic wasps.
Plant borage near tomatoes if you want more pollinator activity in that part of the garden generally - it's also edible, attractive to beneficial predatory insects, and a genuinely useful addition on its own terms. Just hold the yield claim loosely; the mechanism is sound, the proof of the outcome isn't there yet.
Spacing
Borage grows into a sprawling, bristly plant 1-2 feet across, so give it 18-24 inches from a tomato's main stem - close enough that pollinators visiting it will also pass over nearby tomato flowers, far enough that it won't smother the base of the plant or block airflow.
Watch For
Borage self-seeds aggressively once it flowers, so expect volunteer seedlings coming up in that bed in future seasons if you let plants go to seed - not a problem if you want it back, worth knowing if you rotate crops through that spot. It also grows fast and can flop over onto neighboring plants; a light stake or simply cutting it back after its first flush of bloom keeps it from swamping a young tomato.
Frequently Asked Questions
Does letting borage self-seed near tomatoes eventually turn into a weed problem?
Left unmanaged, a few seasons of dropped seed can turn one deliberate planting into scattered seedlings across that whole corner of the garden - nothing like mint's underground spread, but enough to notice by year three or four. Deadhead before seed set if you want to keep it contained, or just treat spring volunteers as a free source of plants to thin down to the ones you actually want.
Is borage worth growing even without tomatoes nearby?
Yes - it's a strong general pollinator plant, the flowers and young leaves are edible with a mild cucumber flavor, and it attracts predatory insects like hoverflies that help with aphid control across the whole garden, not just near tomatoes.