Most companion planting charts will tell you collards love dill, hate tomatoes, and want onions nearby. Almost none of that has been tested. What has been tested, in real trials, is a border of mustard, a bed you have not grown brassicas in for three years, and enough space between plants that a mature collard is not fighting its neighbour for light.
So this article splits the advice in two: what extension services and published trials support, and what is garden tradition passed along until it sounded like fact. Both are useful to know. Only one is worth planning a fall bed around.
Below: how much room a collard actually needs, the pests that show up in a fall bed, the one companion pairing with measured trial data behind it, what the popular chart gets wrong, and the rotation rule that matters more than any of it.
Key Takeaway
The best-supported companion for collards is a border row of mustard, planted as a trap crop rather than a neighbour. Everything else in the popular chart is either neutral, unstudied, or a spacing decision dressed up as a plant relationship.
More than you think, and this single number decides which companions fit. A collard is a non-heading cabbage that keeps producing leaves from a central stem for months, so it gets large and it stays large.
| Source | Row spacing | In-row spacing |
| UF/IFAS Vegetable Production Handbook | 24 to 36 in. (61 to 91 cm) | 12 to 24 in. (30 to 61 cm) |
| Clemson HGIC | 18 to 36 in. (46 to 91 cm) | 6 to 18 in. (15 to 46 cm) |
| University of Georgia Extension | 30 in. (76 cm) | 8 to 16 in. (20 to 41 cm) |
Sources: UF/IFAS Vegetable Production Handbook of Florida, Clemson HGIC Collards, University of Georgia Extension, Home Gardening, 2023.
Read across those tables and a full-size collard occupies a circle roughly 18 to 24 inches across, about 1.5 to 2 square feet per plant. In a 4 by 8 foot raised bed that is eight to twelve plants, and it means anything you interplant has to be short, shallow-rooted, and finished before the collards close over. Sweet alyssum and cilantro fit that description. A second brassica does not.
Days to maturity give you the other half of the plan. Clemson puts direct-seeded collards at 60 to 80 days, UGA at 55 to 70, and UF/IFAS at 70 to 90 days from seed or 50 to 70 from transplants. Georgia's fall window runs 1 August to 1 October in Middle Georgia, two weeks earlier in the north of the state. Soil pH wants to sit at 6.0 to 6.5, which is not only about nutrient availability: low pH favours clubroot.
Four caterpillars and two sap feeders account for most fall collard damage. Cabbage looper leaves ragged holes near leaf edges and moves in a looping crawl. Imported cabbageworm is the velvety green larva of the white butterfly you keep seeing. Diamondback moth larvae feed underneath and leave window-pane damage where the upper leaf surface stays intact, and they are notorious for insecticide resistance. Cabbage aphids cluster grey on leaf undersides.
Then there is harlequin bug, and in the Southeast it is often worse in fall than spring. It sucks sap, leaving white and yellow stippling, and heavy pressure kills plants outright.
Here is the one companion pairing with a number attached. A Virginia Tech SARE project planted 'Southern Giant Curled' mustard as a border-row trap crop around 'Champion' collards and kept harlequin bug feeding damage below 25 percent on the collard crop. The mechanism is documented too: male harlequin bugs track mustard volatiles by smell, then release an aggregation pheromone that pulls in more bugs, concentrating the population on the sacrificial border.
Diamondback moth trap cropping works on a related principle. Trials found glossy collards, Indian mustard and yellow rocket attract far more eggs than cabbage, while larval survival on yellow rocket is minimal, making it a dead-end host. The moth lays where its offspring cannot finish developing.
The Honest Gap in the Evidence
Studies in cabbage and broccoli show that alyssum, dill, cilantro and buckwheat raise parasitoid numbers and cut pest damage. Collard-specific trials measuring those percentages do not exist in the extension literature. Planting them is a reasonable bet based on related brassicas. It is not a documented collard result, and anyone quoting you an exact percentage for collards is extrapolating.
Check what grew there last
Cornell advises not planting collards or other cole crops in the same spot more than once every three or four years. If clubroot has ever been diagnosed in that bed, Oregon State recommends five or six years out of brassicas, because the resting spores have a half-life of about 3.6 years.
Set collards at final spacing, not nursery spacing
Space plants 12 to 18 inches apart in rows 24 to 30 inches apart. Crowding is the most common cause of a disappointing fall bed, and it makes every pest problem worse by trapping humidity and hiding caterpillars.
Put mustard on the perimeter, not in the bed
A trap crop works by being somewhere else. Plant a border row of mustard along the edge that faces open ground or last year's brassicas, and accept that it will look terrible by November. That is the job.
Fill the gaps with short flowering plants
Sweet alyssum, cilantro and dill are low, quick and shallow-rooted, so they use the space before the collards close over. Extension recommends them for beneficial insects generally rather than for collards specifically, and they cost nothing to try.
Use row cover from planting, not after damage appears
Cornell recommends floating row cover from planting to exclude egg-laying moths and butterflies. This is the single most effective thing on this list, and it works whether or not you plant a single companion. Our guide to what row cover actually buys you covers the temperature side.
Why This Works: Stacking Functions in One Bed
The mustard border does three jobs at once. It pulls harlequin bugs off the crop, it flowers and feeds beneficial insects, and when you pull it in winter it goes back into the soil as biomass. That is stacking functions, one of the core permaculture design ideas: choose the element that earns its space several ways rather than the one that does a single job well.
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Send Me the ChartOther brassicas, and that is mostly it. Kale, cabbage, broccoli, kohlrabi, turnips and mustard all share the same pests and the same soil-borne diseases, so packing them together concentrates the problem and shortens how long you can keep the family out of that bed.
The rest of the "do not plant" list does not hold up. Extension sources contain no evidence that tomatoes, peppers, onions, garlic, beans or peas are problematic neighbours for collards. They share no major brassica pathogens and none of the specialised pests. From a disease and pest standpoint they are neutral to mildly helpful, because they break up host continuity.
The bean question deserves a direct answer, because it is the one gardeners ask most. Planting beans next to collards does not feed them nitrogen this season. Most fixed nitrogen stays locked in the legume's own tissue until it dies and decomposes, which is why legumes belong in the rotation ahead of a heavy feeder rather than alongside it.
Key Takeaway
If you want one rule instead of a chart: keep brassicas apart from each other and away from ground that grew brassicas recently. Rotation and spacing do more for a fall collard bed than any companion pairing on the internet, and unlike most of that advice, they are supported.
Other members of the cabbage family, mainly. Kale, cabbage, broccoli, Brussels sprouts, kohlrabi and turnips share collards' pests and soil-borne diseases, so grouping them concentrates cabbageworms, diamondback moth and clubroot risk in one place. Beyond that, extension literature does not support the usual chart warnings. There is no documented reason to keep tomatoes, peppers, onions, garlic, beans or peas away from collards. If you want to grow them nearby, spacing and light are the real constraints, not any plant relationship.
In the same bed, that is two brassicas sharing pests, so it is not ideal. As a deliberate border, it is the best-evidenced companion pairing collards have. A Virginia Tech SARE project used 'Southern Giant Curled' mustard as a perimeter trap crop around collards and held harlequin bug feeding damage below 25 percent on the crop. The point is separation: the mustard sits on the edge and takes the hit, and you accept that it will end the season chewed to pieces.
Yes, with a caveat about timing rather than compatibility. Lettuce is shallow-rooted, quick and low, so it uses bed space before collards reach full size. They share no significant pests or diseases. The limit is light: once a collard spreads to 18 to 24 inches across, anything underneath it is in shade. Sow lettuce at the same time as you transplant collards and plan to harvest it before the canopy closes, roughly six to eight weeks in.
Extension recommendations cluster around 12 to 18 inches between plants with rows 24 to 30 inches apart, though the published ranges are wider. UF/IFAS gives 12 to 24 inches in-row with 24 to 36 inch rows, Clemson gives 6 to 18 inches in-row, and University of Georgia recommends 8 to 16 inches with rows 30 inches apart. Closer spacing produces smaller leaves and more of them; wider spacing gives full-size plants you can harvest from for months. In a raised bed, budget 1.5 to 2 square feet per plant.
Cornell recommends no more than once every three or four years for collards and other cole crops, which reduces the build-up of downy mildew, Alternaria leaf spot and other host-specific pathogens. If clubroot has been diagnosed in that bed, Oregon State University Extension advises five or six years out of brassicas, since clubroot resting spores have a half-life of roughly 3.6 years. Combine the longer rotation with liming to raise pH and with resistant cultivars where you can find them. Our companion planting chart covers how rotation and pairing decisions fit together across the whole garden.
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