Clubroot is a disease that attacks from below, and by the time you see it above ground it has already done its worst. Cabbages, broccoli, cauliflower, and other brassicas grow slowly, turn yellow or purple, and wilt on warm afternoons even though the soil is moist. Pull one up and the reason is obvious: the roots are swollen into thick, knobbly clubs and galls instead of fine, branching roots, and there is almost no fine root left to take up water. The plant is starving and thirsty at the same time, because its root system has been turned into a distorted mass that cannot do its job.
The cause is Plasmodiophora brassicae, a soil organism that is not a true fungus but behaves like one in the garden. It infects the roots of brassicas, triggers the swelling, and produces resting spores that can survive in soil for many years — a decade or more. It favours acid, wet, poorly drained soil, and it spreads in soil on tools, boots, and transplants. There is no cure for an infected plant, and no spray that will clean infested soil, so clubroot management is about keeping it out, making the soil less welcoming, growing resistant varieties, and rotating brassicas away from infested ground for a long time.
What clubroot looks like: symptoms
- Swollen, clubbed roots: the classic sign — roots thickened into irregular clubs, galls, and knobbly masses, with few or no fine feeder roots.
- Stunting: infected plants are much smaller than their neighbours, with small, pale leaves and no heart forming in cabbage or cauliflower.
- Yellowing and purpling: leaves turn yellow, sometimes with a purple tinge, especially on the older leaves, as the plant fails to take up nutrients.
- Wilting on warm days: plants wilt in the afternoon heat and recover overnight at first, then stop recovering, even though the soil is moist.
- Wilting that does not respond to watering: the defining frustration — watering does not perk the plant up, because the roots cannot absorb the water.
- Poor or no heading: cabbages fail to form heads, cauliflowers make tiny curds or none, and broccoli makes small, loose heads.
- Death in severe cases: badly infected young plants may die outright, while older plants linger, stunted, for the rest of the season.
Clubroot infection starts soon after transplanting or germination, when the resting spores in the soil germinate and infect the young roots. The swelling develops over the following weeks, and the above-ground symptoms — stunting, yellowing, and afternoon wilting — usually appear in midsummer, when the plant's water demand is highest and its crippled roots cannot keep up. The disease gets worse through the season as the clubs grow and the fine roots die back. A plant infected young may die within weeks; a plant infected later may survive to produce a small, poor head. The resting spores are released into the soil as the clubs rot, so the infestation grows worse with every brassica crop grown in the same ground.
Which plants get clubroot
Clubroot attacks the brassica family: cabbage, broccoli, cauliflower, kale, Brussels sprouts, kohlrabi, turnips, swedes, radishes, mustard, and oilseed rape, along with brassica weeds such as shepherd's purse, charlock, and wild radish, which keep the disease alive in the soil even when no crop is present. It does not attack plants outside the brassica family, so a bed that is ruined for cabbage can still grow potatoes, beans, or lettuce perfectly well. That family specificity is the key to managing it through rotation.
Conditions that favour clubroot
Clubroot favours acid soil, with a pH below about 7, and wet, poorly drained, compacted soil. It is worst in cool, moist conditions in spring and autumn, and it is more severe in light, sandy soils and in soils low in calcium. The resting spores survive in soil for many years, and they build up with every brassica crop, so a bed that has grown brassicas year after year is at the highest risk. Transplants raised in infested soil or compost carry the disease into a clean bed, and soil moved on tools and boots spreads it from bed to bed. Warm, dry, alkaline, well-drained soil with plenty of calcium is the least welcoming environment for it.
How clubroot spreads
Clubroot spreads through soil: on tools, boots, pots, and transplants, in soil moved from one bed to another, and in drainage water. It also travels in infected transplants raised in contaminated mix, which is the most common way it reaches a new garden. The resting spores are extremely tough and survive in soil for a decade or more, in compost that did not get hot enough, and in the roots of brassica weeds. It does not spread through the air, and insects are not a significant carrier. The practical rule is that anything carrying soil from an infested bed can carry clubroot.
How to tell it apart from lookalikes
Clubroot is sometimes confused with root-knot nematodes, which also swell roots, but nematode galls are small, round, and bead-like, while clubroot makes large, irregular, knobbly clubs that distort the whole root. Drought wilting looks similar above ground, but the soil is dry and the roots look normal. Nutrient deficiency yellows leaves without wilting them and without root swelling. Cabbage root fly damage also stunts brassicas, but the roots show feeding damage and small white maggots rather than clubs. Pulling the plant up settles it: clubbed roots are unmistakable.
Prevention: cultural steps that work
- Raise brassicas from clean seed in fresh, sterile mix, and buy transplants only from reputable sources. Never accept plants grown in soil from a garden with clubroot.
- Rotate brassicas so they do not return to the same bed for at least four years, and ideally seven, and keep brassica weeds down so the disease has no host in between.
- Raise the soil pH toward neutral or slightly alkaline by adding garden lime as advised by a soil test — clubroot is much less severe above pH 7.
- Improve drainage with compost and coarse organic matter, and grow brassicas in raised beds where the soil is wet or heavy.
- Add calcium-rich material such as ground limestone where a soil test shows calcium is low, and avoid fresh manure, which can favour the disease.
- Clean tools, boots, and pots after working in an infested bed, and work in healthy beds before infested ones.
- Grow resistant varieties where they are available — clubroot-resistant cabbage, broccoli, and other brassicas exist and are worth seeking out.
Treatment step by step
- There is no cure for a plant that already has clubroot. Pull out infected plants as soon as you are sure, with as much root as possible, and dispose of them with household waste — never compost them.
- Do not plant any brassica in the affected bed for at least four years, and longer if the infestation is severe. Use the bed for potatoes, beans, sweet corn, or other non-brassicas instead.
- Test the soil pH and add garden lime to bring it toward neutral or slightly alkaline, following the test recommendations rather than guessing.
- Improve the drainage of the bed with compost and coarse organic matter, or switch the brassicas to a raised bed with fresh, clean soil.
- Keep brassica weeds down in and around the bed, since they host the disease and keep it alive in the soil.
- Clean every tool, boot, and pot that touched the infested bed before using it elsewhere, and do not move soil from the affected bed.
- If you must grow brassicas in infested soil, choose a resistant variety and grow it in a container or a raised bed filled with fresh, clean mix.
What recovery looks like
An infected plant does not recover from clubroot — the swollen roots cannot be unswollen, and the plant will stay stunted for the season. Recovery belongs to the soil and to the gardener's planning: a bed managed with liming, drainage, rotation, and resistant varieties becomes productive for brassicas again, though it may take several years. The sign that the plan is working is a brassica crop that grows normally, with no wilting on warm afternoons and no clubs on the roots when you pull a plant at the end of the season. Many gardeners find that a combination of resistant varieties and a limed, well-drained raised bed lets them grow brassicas successfully even where clubroot is present in the wider garden.
When a plant is beyond saving
A plant is beyond saving once its roots are clubbed and it is wilting despite moist soil — remove it promptly so it does not shed more spores into the bed. A bed is not permanently ruined, but it is out of bounds for susceptible brassicas for years unless you use resistant varieties or grow in fresh containers. A garden where clubroot returns every year despite liming and rotation needs a longer rotation, stricter weed control, and a switch to resistant varieties — and a soil test from your local extension service will tell you whether the pH and calcium are actually where they need to be.
Frequently asked questions
Can I eat a cabbage with clubroot?
The swollen roots are the problem, not the leaves, and the disease does not make the plant poisonous — but an infected plant is usually so stunted and poor that it is not worth eating. Remove the plant and dispose of it rather than harvesting from it.
Will liming my soil cure clubroot?
Liming reduces the severity of clubroot by raising the pH and adding calcium, but it does not eliminate the resting spores. It is one part of a plan that also needs rotation, resistant varieties, and clean transplants.
How long does clubroot survive in soil?
The resting spores can survive for a decade or more without a host. That is why the rotation needs to be long and why brassica weeds must be controlled — they keep the disease alive in between crops.
Can I grow brassicas in pots if my soil has clubroot?
Yes, and it is one of the best workarounds. Grow them in containers or raised beds filled with fresh, clean mix, and keep the containers away from infested soil and splash.
Does clubroot affect anything other than brassicas?
No. Clubroot attacks the brassica family only, including brassica weeds. Other vegetables — potatoes, beans, lettuce, tomatoes, sweet corn — are not hosts, which is what makes rotation possible.
Getting help and going further
If you are unsure which disease you are dealing with, take clear photos of the symptoms and check your local extension service — they can confirm a diagnosis from a sample and advise on the varieties and the timing that work best in your area. You can also try our plant disease checker to narrow down the problem, and browse the guides hub for related disease guides. For growing advice, see growing broccoli. For growing advice, see growing cabbage. For growing advice, see growing cauliflower. Related guides: root rot treatment, fusarium wilt, crown rot. Whenever you remove diseased material, dispose of it with household waste — do not compost diseased material, since home compost rarely gets hot enough to kill the organisms that cause these diseases. Good record-keeping helps too: note the date, the weather, and the variety when a problem first appears, so you can spot the pattern next year and act earlier.