Garden Problems: What Is Wrong With My Vegetables?

Start with what you can see

Gardeners rarely know the cause at first. They know the symptom. Pick the one closest to yours:

• Ragged holes and slime trails, worst on seedlings: slugs and snails
• Holes in cabbage-family leaves, green droppings: cabbage caterpillars
• Curled, sticky leaves, often with black mould: aphids
• A white, powdery coating on leaves: powdery mildew
• Brown, collapsing tomato or potato leaves after warm, wet weather: tomato and potato blight
• A dark, sunken patch on the bottom of tomatoes: blossom end rot
• Yellow leaves: why leaves turn yellow
• Wilting in wet soil: overwatered plants
• Lettuce or spinach shooting up and turning bitter: bolting
• Seedlings toppling at soil level: damping off
• Nothing came up: seeds not germinating
• Rusty tunnels in carrots: carrot fly
• Stunted cabbages with swollen roots: clubroot
• Plants that just sit there: why plants are not growing
• Heavy, sticky or dusty ground: soil problems

Pest guides

• Slugs and snails: night-time grazers of seedlings and soft growth.
• Aphids: sap-suckers that curl leaves and leave sticky honeydew.
• Carrot fly: larvae that tunnel into carrots, parsnips and celery.
• Cabbage caterpillars: white butterfly and cabbage moth larvae on brassicas.

Disease guides

• Powdery mildew: a white coating on courgette, squash and pea leaves.
• Clubroot: swollen roots and stunted cabbage-family plants.
• Tomato and potato blight: fast brown rot of leaves, fruit and tubers in warm, wet weather.

Growing problem guides

• Seeds not germinating: why a row fails to come up.
• Overwatered plants: wilting and yellowing in wet soil.
• Plants not growing: five causes to check in order.
• Soil problems: clay, sand, compaction and pH.
• Damping off: seedlings that topple at soil level.
• Blossom end rot: black, sunken patches on tomatoes and peppers.
• Bolting: lettuce and spinach running to seed.
• Yellow leaves: reading the pattern to find the cause.

Pests: who is eating your crops?

Most pest damage comes from a handful of culprits. Slugs and snails feed mostly at night, so the damage appears with nobody in sight. Aphids suck sap and leave sticky honeydew on which sooty mould grows. The caterpillars of the white butterflies and the cabbage moth go for the cabbage family, and carrot fly larvae tunnel into carrots, parsnips and celery. Each has its own page: slugs and snails, aphids, cabbage caterpillars, carrot fly.

Diseases: blight, mildew and clubroot

Three diseases cause most of the heartbreak. Late blight attacks potatoes and tomatoes and spreads fast in warm, wet weather. Powdery mildew whitens courgette, squash and pea leaves, and unlike most diseases it is common in warm, dry weather. Clubroot swells the roots of the cabbage family and stays in the soil for years. Read blight, powdery mildew and clubroot.

When the problem is the growing conditions

Plenty of problems have no pest or disease behind them at all. Blossom end rot is a disorder caused by uneven watering, not an infection. Waterlogged soil drowns roots by pushing out the air. Heat and long days make lettuce and spinach bolt. Yellow leaves can mean poor drainage, damaged roots, a pH problem or hungry plants. See blossom end rot, overwatering, bolting and yellow leaves.

Seeds and seedlings

Cold soil is the commonest reason seeds fail. Seedlings that come up and then topple at the base usually have damping off, which thrives in wet compost and crowded, still air. Start with seeds not germinating and damping off.

Soil: the problem under every other problem

Heavy clay drains slowly and warms late in spring, while sand drains fast and dries out. Organic matter improves both, and a soil test shows what is actually wrong before you add anything. Read soil problems and why plants are not growing.

Four habits that prevent most problems

• Cover crops at risk: fine mesh keeps cabbage butterflies and carrot fly off.
• Water steadily, in the morning, at the base of the plant.
• Feed with compost rather than heavy doses of nitrogen, which favours aphids.
• Encourage the predators: ladybirds, hoverflies, lacewings, ground beetles, birds and hedgehogs.

Garden problem questions

Sources and further reading

• RHS: Slugs and snails
• UC IPM (University of California): Snails and slugs
• University of Wisconsin–Madison Extension: Slugs
• Oregon State University Extension: How to control slugs in your garden
• RHS: Aphids
• UC IPM (University of California): Aphids
• University of Wisconsin–Madison Extension: Aphids
• University of Illinois Extension: Aphid
• RHS: Cabbage caterpillars
• University of Wisconsin–Madison Extension: Imported cabbageworm
• University of Illinois Extension: Cabbageworm
• RHS: Carrot fly
• Utah State University Extension: Carrot rust fly
• UC IPM (University of California): Carrot rust fly
• RHS: Potato blight
• RHS: Tomato blight
• University of Wisconsin–Madison Extension: Late blight
• UC IPM (University of California): Powdery mildew on fruits and berries
• University of Wisconsin–Madison Extension: Powdery mildew
• University of Saskatchewan, Gardening at USask: Clubroot
• University of Wisconsin–Madison Extension: Cole crops disorder: clubroot (A1128)
• University of Wisconsin–Madison Extension: Blossom end rot
• RHS: Blossom end rot
• RHS: Grow your own: August jobs
• RHS: Waterlogging and flooding
• Utah State University Extension: Overwatering
• University of Illinois Extension: Drowning and edema
• Utah State University Extension: Leafy greens: physiological problems
• University of Illinois Extension: Spring greens
• University of Illinois Extension: Yellow leaves can indicate plant problems
• RHS: Nutrient deficiencies
• University of Saskatchewan, Gardening at USask: Poor vegetable seed germination
• Utah State University Extension: Starting vegetable seeds indoors: germination
• RHS: Damping off
• Penn State Extension: Damping off
• Utah State University Extension: Damping-off (fact sheet)
• RHS: Soil types
• RHS: Organic matter: how to use it in the garden
• Colorado State University Extension: Plant nutrition
• University of Illinois Extension: Give your soil a check-up this fall
• University of Wisconsin–Madison Extension: Fall is a good time to test lawn and garden soil
• Utah State University Extension: Imported cabbageworm
• Utah State University Extension: Aphids on vegetables

Facts on this page are summarised in our own words from the pages above; each is supported by at least two of them, or by one plus well-established growing science (noted in our research file). Every source was opened and checked on 23 October 2026.

Keep a garden record

Most problems come back to the same beds in the same weeks. A simple record of what grew where, and when trouble started, lets you get ahead of it next year. Sketch your beds in the free Vegetable Garden Layout Planner Tool, and keep sowing dates, problems and harvests in the Global Vegetable Garden Planner (printable PDF). Every crop we cover is in the vegetable growing guides.