Peppers and Kohlrabi
Antagonist Pair — Keep Apart
We don't know of a controlled trial measuring reduced pepper yield specifically from nearby kohlrabi. This antagonist listing is really a nutrient-budgeting caution rather than a documented chemical or disease conflict - two heavy feeders sharing tight soil is a real practical concern even without a specific study behind this exact pair.
Mechanism: Nutrient Competition
Kohlrabi is a fast, heavy-feeding brassica that bulks up its swollen stem in just 45-60 days, pulling hard on soil nitrogen during that window, and peppers are themselves demanding, slow-maturing feeders over a 60-90 day season - putting two aggressive feeders that close together asks more of a bed's soil fertility than most home gardeners are topping up for.
Kohlrabi doesn't threaten peppers with disease or chemical suppression the way some antagonist pairs on this site do - it's a subtler, more mundane conflict, and one that's easy to work around with timing rather than treating the two as incompatible outright.
A Scheduling Fix, Not a Strict Separation
Because kohlrabi is frost-hardy and matures fast while peppers are frost-tender and need warm soil, the two crops naturally occupy different windows of the season in most climates - a spring kohlrabi crop can be harvested and cleared well before peppers even go outside. Treated as a succession rather than a simultaneous pairing, the nutrient-competition concern mostly disappears.
Spacing
If you grow both anyway, kohlrabi's 6-8 inch spacing means it should go in its own section of the bed rather than directly under a pepper's canopy - give at least a full pepper spacing's worth of separation (12-18 inches) so their root zones aren't drawing from the same patch of soil at once.
Watch For
Kohlrabi is frost-hardy and can be sown well before peppers go outside, so the more practical fix is timing rather than distance: get an early kohlrabi crop harvested and out of the bed before warm-season peppers are transplanted, rather than growing the two side by side for their full seasons.
Frequently Asked Questions
Can I plant peppers where kohlrabi just grew?
Yes - once kohlrabi is harvested, work some compost into that spot before transplanting peppers, since kohlrabi is a heavy feeder and will have drawn down the soil's nitrogen. A quick top-up avoids most of the nutrient-competition concern that comes from growing them simultaneously.