Guides
Something is wrong with your plant.
Work out what you are looking at, then deal with it. Every page here starts with prevention and barriers, brings in the predators that do the job for free, and reaches for a product last, if at all.
Pests
Insects, mites, molluscs and the occasional mammal. Each page covers what the damage looks like, what to do about it now, and how to keep the predators that would otherwise handle it for you.
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Aphids
Aphidoidea
How to recognise aphids on roses, beans and houseplants, tell them apart from whitefly and scale, and clear them without reaching for a spray.
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Box tree caterpillar
Cydalima perspectalis
Webbing, bare brown patches and a hedge eaten in a fortnight. How to spot box tree caterpillar early, why the bark damage is what kills, and what works against it.
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Cabbage root fly
Delia radicum
Brassica transplants wilting and dying within a week of planting, with white maggots in the roots. How a collar at the stem stops the fly laying, and when the three flights arrive.
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Capsid bugs
Miridae
Small tattered holes with brown edges in the newest leaves, and no insect anywhere. How capsid damage appears weeks after the bug has moved on, and why it is worth tolerating.
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Carrot fly
Chamaepsila rosae
Bronzed carrot tops and rust-brown tunnels through the roots. Why the fly cannot climb, how a low barrier works, and the sowing dates that miss both generations.
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Caterpillars
Lepidoptera
How to tell a caterpillar from a sawfly larva by counting its legs, which few species are worth acting on, and why netting beats everything else on brassicas.
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Codling moth
Cydia pomonella
A tunnel to the core packed with wet brown frass. How codling moth differs from apple sawfly, what a pheromone trap is worth, and the cardboard band that catches the larvae.
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Earwigs and ants
Earwigs eat more aphids than petals, and ants are farming the greenfly rather than eating your plant. What each one is doing, and the rare cases where either needs managing.
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Fungus gnats
Sciaridae
Small dark flies drifting up from the compost every time you water. What the larvae are eating, why they are far less harmful than they look, and the one change that ends it.
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Leaf miners
Pale squiggles and brown blotches with both leaf surfaces still intact. Which leaf miners matter in a British garden, why sprays cannot reach them, and what raking up in autumn is worth.
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Leatherjackets and chafer grubs
Yellow patches of lawn that lift like a carpet, and birds or badgers tearing the turf apart. How to tell the two grubs apart and when nematodes work against them.
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Mealybug
Pseudococcidae
Small blobs of cotton wool in the leaf axils of a hoya, an orchid or a cactus. Why the wax makes sprays useless, and the cotton bud that works instead.
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Rabbits and deer
Shoots cut clean at an angle, or torn off ragged. One tells you rabbits and the other deer, and the fence you need is different for each.
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Red spider mite
Tetranychus urticae
Fine pale speckling on the upper leaf and webbing at the shoot tips. How to confirm red spider mite with a sheet of paper, and why the fix is humidity rather than a spray.
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Sawflies
Symphyta
Gooseberries stripped to the ribs, rose leaves skeletonised, aquilegia bare by June. How to recognise sawfly larvae by counting their legs, and why caterpillar treatments do nothing to them.
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Scale insects
Coccoidea
Brown or yellowish domes stuck to stems and leaf veins, and sticky leaves under them. Why they will not move when you push them, and the fortnight in summer when they can be stopped.
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Scarlet lily beetle
Lilioceris lilii
A bright red beetle on a lily, and orange grubs hidden under their own droppings. Why hand picking from March beats anything else, and what the beetle will and will not breed on.
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Slugs and snails
Gastropoda
How to tell slug damage from everything else that eats a leaf, which of the forty-odd British species are worth worrying about, and what works since the old pellets were banned.
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Squirrels and mice
Crocuses excavated in November, a row of peas gone before it germinated, bark stripped off a young tree. What each rodent does, and why poison is the wrong answer in a garden.
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Thrips
Thysanoptera
Slender insects a millimetre long that rasp the surface off a leaf. How to tell thrips damage from spider mite, and why half their life cycle happens in the compost.
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Viburnum beetle
Pyrrhalta viburni
Viburnum leaves reduced to a skeleton of veins in May and again in August. Why checking the shoot tips in winter is the one control that works, and which viburnums escape.
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Vine weevil
Otiorhynchus sulcatus
The adult cuts neat semicircles out of leaf edges and does no real harm. The grub eats the roots off a container plant over winter. How to recognise both, and when nematodes work.
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Whitefly
Aleyrodidae
Tiny white insects on the undersides of the youngest leaves, sticky foliage below. Why spraying the adults changes nothing, and the parasitoid wasp that has worked since the 1920s.
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Wood pigeons
Columba palumbus
Cabbages and sprouts reduced to bare midribs between November and March. Why netting is the only thing that works on wood pigeons, and how to fit it without trapping anything.
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Woolly aphid
Eriosoma lanigerum
Tufts of white wool in the bark cracks of an apple, cotoneaster or pyracantha, with lumpy swellings underneath. Why the swellings matter more than the wool, and what a stiff brush achieves.
Diseases
Fungi, oomycetes, bacteria and viruses. Several of these have no cure available to a gardener, and those pages say so and cover what to plant instead rather than offering a treatment that will not work.
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Allium white rot
Stromatinia cepivora
Onions and garlic yellowing and pulling out of the ground with white fluff and black grains at the base. Why white rot outlasts any rotation, and how to keep growing alliums anyway.
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Apple and pear scab
Venturia inaequalis
Olive-black velvety blotches on the leaves and rough corky patches on the fruit. Why raking leaves in autumn is the whole treatment now, and which cultivars shrug it off.
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Ash dieback
Hymenoscyphus fraxineus
Thinning crowns, diamond lesions on the stems and bushy growth from the trunk. Why felling a healthy-looking ash is the wrong response, and when a tree needs professional assessment.
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Bacterial canker
Pseudomonas syringae
Amber gum weeping from sunken bark on a cherry or plum, buds that never open, and shot holes in the leaves. Why summer is the only safe time to prune, and how to cut ahead of it.
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Blackleg
Pectobacterium atrosepticum
A potato plant yellowing and toppling with a slimy black stem base. Where blackleg comes from, why certified seed is the whole prevention, and how it turns into soft rot in store.
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Blight
Phytophthora infestans
Brown blotches on the leaves and a crop lost in a week. What a Hutton Period is, why blight is not a fungus, and how to save the potatoes once the foliage has gone.
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Box blight
Calonectria pseudonaviculata
Brown leaves falling from a box hedge, black streaks on the green stems and bald patches that spread. How box blight moves, why clipping makes it worse, and how to keep a hedge.
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Brown rot
Monilinia fructigena
Apples and plums rotting on the tree in concentric rings of buff pustules, then shrivelling to hard black mummies. Why picking the mummies off in winter is the whole control.
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Clubroot
Plasmodiophora brassicae
Cabbages that wilt in the sun and recover overnight, and roots swollen into clubs. Why clubroot cannot be dug out or sprayed away, and how to keep growing brassicas on land that has it.
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Coral spot
Nectria cinnabarina
Coral-pink cushions studding a dead branch, and dieback on a maple or a magnolia. Why coral spot is mostly harmless until you give it a way in, and what your pea sticks have to do with it.
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Damping off
A tray of seedlings that were fine yesterday, toppled over this morning with pinched dark stems. The conditions that cause it, and why the water butt is part of the problem.
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Downy mildew
Peronosporaceae
Angular yellow blotches penned in by the veins, with a grey or purple bloom on the underside. Why downy mildew is the opposite of powdery mildew in almost every respect.
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Fireblight
Erwinia amylovora
Blossom browning overnight, shoot tips hooked over like a shepherd's crook, and leaves that go black but stay on. How to cut ahead of fireblight and which plants it cannot touch.
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Grey mould
Botrytis cinerea
Fuzzy grey growth on fruit, seedlings and greenhouse plants, puffing spores when touched. Why it needs dead tissue to get started, and what ventilation has to do with it.
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Honey fungus
Armillaria
The most destructive fungal disease of garden trees and shrubs in Britain. The three signs that confirm it, why no treatment exists, and what you can plant instead.
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Mosaic virus
Dark and pale green blotching, puckered leaves and misshapen fruit. How to tell a mosaic virus from a feeding problem, why there is no treatment, and how to stop it spreading.
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Peach leaf curl
Taphrina deformans
Peach and nectarine leaves emerging thickened, puckered and crimson in spring. Why the infection happens before the leaves open, and how a sheet of polythene from January prevents it.
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Potato scab
Streptomyces scabiei
Corky scabs on potato skins that go no deeper than the peel. Why common scab is a watering problem rather than a soil disease, and how the opposite conditions cause powdery scab.
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Powdery mildew
White powdery patches on courgettes, roses and oak. Why watering more is the fix rather than watering less, and why the mildew on one plant will not spread to the next.
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Red thread
Laetisaria fuciformis
Bleached patches in a lawn with pink threads on the grass tips. Red thread looks alarming, kills nothing, and usually means the lawn is short of nitrogen.
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Rose black spot
Diplocarpon rosae
Dark fringed blotches on rose leaves, yellowing around them, and a bare bush by late summer. What the green rings mean, and why cleaner air made this worse.
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Rust
Pucciniales
Rusty spots on the underside of a leaf and yellow blotches above. Why rust on your leeks cannot reach your roses, and why the fix is dry foliage rather than a spray.
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Silver leaf
Chondrostereum purpureum
Leaves on one branch of a plum turning a dull silver, and a purple stain inside the dead wood. How to confirm it with one cut, and why plums are pruned in June.
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Sooty mould
Leaves turning black and sticky under a tree or a houseplant. Sooty mould grows on the honeydew that sap-sucking insects drip, so the fix is whatever is feeding overhead.
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Verticillium wilt
Verticillium dahliae
A maple losing one branch a year while the rest looks well. How to confirm verticillium wilt with a single cut, and what can safely be planted in the same ground afterwards.
Disorders
Watering, light, temperature and feeding. Nothing has infected the plant and nothing is eating it, so the fix is a change of habit rather than a treatment, and these are the problems behind most of the yellow leaves on most windowsills.
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Blossom drop
Tomatoes, beans and courgettes flowering freely and setting nothing. The temperature limits pollen works within, why courgettes drop their first flowers, and what to do at midday.
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Blossom end rot
A black leathery patch on the bottom of a tomato. Why adding calcium almost never helps in British soil, and what steady watering has to do with it.
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Bolting
Crops shooting up a flower stem before they are ready to eat. The two separate triggers behind it, why the plant cannot be talked out of it, and how to sow so it does not happen.
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Bud drop
A gardenia, camellia or Christmas cactus covered in buds that drop before opening. The three things that cause it, and why moving the plant is usually what did it.
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Drought stress
A wilting plant may be dry or drowning, and the treatments are opposite. How to read the compost, why a watered pot can still be bone dry inside, and what new trees need.
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Etiolation
Seedlings drawn thin and falling over, and a succulent stretched into a bare stalk. Why etiolated growth never turns back, and how to fix the light rather than the plant.
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Failure to flower
A wisteria in leaf and nothing else, a hydrangea that flowered once, a camellia that never sets buds. The five reasons a plant refuses to flower, in the order worth checking.
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Frost damage
New growth blackened overnight in spring, or a shrub browned by a cold wind in winter. Why late frosts do more harm than deep ones, and why cutting the damage off straight away is a mistake.
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Hard water and salt build-up
A white crust on the compost and the pot, brown leaf tips, and a lime-hater going yellow. What builds up in a container, how to flush it out, and which plants need rainwater.
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Herbicide damage
Tomatoes and beans with fern-like twisted leaves and cupped shoot tips. How to spot aminopyralid in manure or compost before you spread it, and what to do with a contaminated plot.
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Leaf scorch
Bleached patches and brown crisp margins that appeared all at once. How to tell scorch from disease, why evergreens burn in February, and where the water droplet story comes from.
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Nutrient deficiencies
Yellow leaves at the bottom of the plant mean something different from yellow leaves at the top. The rule that halves the diagnosis, and why most yellowing is not a shortage at all.
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Pot bound
A houseplant drying out within a day, water running straight through, and roots out of the drainage holes. When to pot on, when to root prune instead, and the plants that prefer to stay tight.
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Root rot
The commonest way a houseplant dies, and the one where the obvious response makes it worse. How to read the roots, and what to change so it does not happen again.
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Transplant shock
A plant that wilts, drops leaves or stands still for weeks after being moved. What happens at the roots, and the handful of things that shorten it.
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Waterlogging
Yellow leaves, wilting on wet ground and plants dying over winter. Why waterlogged roots suffocate rather than drown, and what to do about a garden that lies wet.
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Wind rock
A shrub or a sprout rocking in the wind until a funnel opens around its base. Why that hole fills with water and kills the plant, and the two minutes in autumn that prevent it.
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