Peas and Turnips
Beneficial Pair — Good Match
As with other legume pairings here, nitrogen fixation itself is well documented, and the genuinely overlapping cool-season timing makes simultaneous benefit more plausible than with mismatched-season pairs. What's still uncertain is how much nitrogen a fast-maturing turnip crop actually draws from an actively growing pea planting within their shared short window, versus the larger release that happens once pea residue breaks down after harvest.
Mechanism: Nitrogen Fixing
Peas fix nitrogen through root nodule bacteria, and turnips are a fast-maturing brassica (30-60 days) that shares peas' cool-season, frost-hardy timing closely enough that the two can genuinely grow side by side rather than needing the succession approach some other legume pairings on this site require - meaning turnips have a real chance to draw on nitrogen the peas are actively contributing to shared soil during the same season, not just residue left behind afterward.
Peas and turnips share enough of the same cool-season window that this pairing avoids the timing problems that complicate some of the other legume-and-root combinations in this reference, even if the nitrogen-sharing question is still more assumption than confirmed measurement.
A Fast Root Crop Alongside a Slower Climber
Because turnips mature in a fraction of the time peas need to finish, the practical rhythm of this bed is turnips coming out first while peas continue climbing and producing, rather than a single simultaneous harvest. That staggered timing is worth planning around - use the turnip harvest as an opportunity to check in on trellis support and thin out any crowded pea vines before they fully take over the remaining space.
Spacing
Turnips' 4-6 inch spacing and peas' tight 2-3 inch spacing fit comfortably in adjacent rows within the same bed, with turnips' broader leaves at ground level and peas climbing upward, so the two aren't competing directly for the same light or root space.
Watch For
Turnips mature quickly enough (in as little as 30 days) that a spring-sown crop is often ready to harvest before peas finish their own season, so plan on turnips being the first thing pulled from this shared bed, with peas continuing on afterward rather than both crops finishing together.
Frequently Asked Questions
In a small raised bed, should I choose a shorter pea variety so it doesn't shade the turnips?
It's a reasonable precaution in tight quarters. A tall, trellised pea casts more shade at ground level than a dwarf or bush pea would, and turnips' broad leaves do best with consistent light while bulking up. In a small bed specifically, a compact pea variety reduces that shading risk more effectively than spacing adjustments alone.