Growing Guide

Pests, remedies, and myths

Garden advice about deer, bugs, and mildew is mostly repeated rather than tested. This guide sorts it for animals, insects, and fungal disease: what to look for, which remedies are folklore, and the short list of things that hold up.

A groundhog standing upright, eating a leaf — Photo: Paul Danese, CC BY-SA 4.0

The Pest-Control Year, Step by Step

When each job goes, timed to your frost dates

Most pest control is timing. Barriers go up before the damage starts, hand-picking runs in the weeks each pest is active, and disease control happens mostly in fall. Add your ZIP to turn every step into your own months and see which one is open now.

Every step counts from your last spring frost or your first fall frost, so the right week here is a different week elsewhere.

Clean up last year's diseased leaves and canes

2–6 weeks before last frost

Rake and bag leaves that carried black spot, leaf spot, or mildew, and cut out cankered canes. Spores overwinter on them and splash up onto the new growth.

2Key move

Fence and cage before new shoots emerge

0–4 weeks before last frost

Deer and rabbits find the first tender growth within days, and a habit is hard to break once it starts. Put cages over hostas, tulips, and new transplants now, and start repellents before the first bite, not after.

Cover brassicas and squash with row cover

around last frost (1 week before to 4 weeks after)

Lay floating cover at planting, edges buried or weighted, so beetles, flea beetles, and egg-laying moths never reach the leaves. Take it off squash and cucumbers when flowers open so pollinators can get in.

Hand-pick slugs and set trap boards

0–8 weeks after last frost

Slugs peak in cool, wet spring weather. Lay a board on the soil, check under it each morning, and go out after dark with a flashlight on the worst nights.

Start protectants only where it comes back every year

around last frost (2 weeks before to 4 weeks after)

A fungicide protects new growth and does nothing for a leaf already infected. If a rose or phlox gets the same disease every year, start before symptoms and renew after heavy rain. If it doesn't, skip it.

Scout weekly for aphids, eggs, and chewing

2–12 weeks after last frost

Turn leaves over. A hard stream of water knocks aphids off, and a week of waiting often brings the ladybugs and hoverflies that finish the job. Act when numbers keep climbing, not on the first one.

Hand-pick beetles and hornworms

8–16 weeks after last frost

Go out in the cool of the morning when beetles are sluggish and knock them into soapy water. Check tomatoes for bare stems and dark droppings, which give hornworms away.

Apply beneficial nematodes for lawn grubs

6–12 weeks before first frost

Only if you have actually dug and counted grubs. Nematodes need warm, moist soil and die in sun, so water the lawn first, apply on a cloudy evening, and keep it damp for two weeks.

9Key move

Rake and bag diseased leaves

around first frost (2 weeks before to 4 weeks after)

The most useful fungus control there is. Anything that carried disease goes in the trash or a municipal compost, not the backyard pile, which rarely gets hot enough to kill it.

Wire bulbs, wrap trunks, and pull mulch back

around first frost (2 weeks before to 4 weeks after)

Cover newly planted bulbs with wire pinned to the soil, put hardware-cloth cylinders around young trunks against rabbits and voles, and pull mulch a hand-width back from bark so voles have nowhere to tunnel under cover.

The Order to Try Things

Seven steps, and most problems stop at three

Reaching for a spray first is the common mistake. Working down this list is cheaper, safer for the bees, and more likely to work.

1. Name it before you treat it

Most wasted spray is aimed at the wrong thing. Look at the damage, the time of day it happens, and what is left behind. Each problem below starts with what its damage looks like, and our insect and fungi pages show the usual suspects.

2. Decide whether it matters

Healthy established plants lose a fair share of their leaves without suffering, and a chewed hosta is an ugly plant, not a dying one. Fruit and vegetable crops and young transplants are the exceptions, because losing the leaves early costs you the harvest.

3. Fix the conditions

Soggy soil, crowded plants, too much nitrogen, and watering at night invite most of the trouble. Spacing, drainage, morning watering at the base, and the right plant in the right spot do more than anything you can spray.

4. Block it

Fences, cages, netting, and row cover beat every repellent, because they work whether the animal is hungry or not. This is the step that actually stops deer, rabbits, birds, and egg-laying moths.

5. Remove it by hand

Hand-picking sounds like too little and works better than people expect on slugs, beetles, and hornworms. Do it small and often, ahead of the numbers getting large.

6. Bring in the helpers

Predators and parasites keep most insects in check if you let them. Flowers for hoverflies and lacewings, a shallow water dish, and a refusal to spray everything at the first sight of an aphid let them build up.

7. Spray last, and narrowly

A targeted product used at the right time, on the right pest, following the label. Broad sprays kill the predators along with the pest and often make the next outbreak worse.

Animals

Fences beat folklore

The right fix for a deer is useless against a vole, and the other way round. The damage usually tells you which one you have. Deer, rabbits, and rodents respond to physical barriers and to very little else. Repellents slow them down, and the smell and sound tricks wear off within days.

Deer

The tellTorn edges, a browse line, and whole shoots missing overnight.

Reading the damageRagged, torn edges on twigs and leaves. Deer. They have no upper front teeth, so they pull and tear instead of cutting. Look for a browse line, a level height beyond which nothing is left, usually around waist to shoulder height, and for split hoof prints in soft soil.

Myths

Human hair, hung soap, and scattered mothballs. They fail within days. Mothballs are a pesticide that is illegal to use this way and poisonous to pets, children, and soil life.
"Deer-resistant" plants. The label means deer prefer something else, not that they will not eat it. A hungry herd in a hard winter eats nearly anything.

What works

A fence at least 8 feet tall, or two shorter fences about 4 feet apart, which deer will not jump because they cannot judge the landing. This is the only thing that fully works.
Repellent sprays on plants, rotated between two products and reapplied after rain and as new growth comes in. They reduce damage and do not stop it, and they work best when started before deer have made the bed a habit.
Cages around young trees and valued shrubs through the first winters.
Planting scented, bitter, or fuzzy plants such as lavender, sage, allium, and daffodils in the outer beds, and tender things nearest the house.

Rabbits

The tellClean 45-degree cuts below knee height, and bark stripped in winter.

Reading the damageA clean slanted cut, low to the ground. Rabbits. They snip stems at about 45 degrees, mostly below knee height, and leave round pellets. In winter they chew bark off young trees and shrubs up to the height of the snow.

Myths

Ultrasonic repellers. Animals ignore them within a few days, and there is no good evidence they work.
Blood meal as a repellent. It smells of something edible, washes off, and can draw in other animals instead.

What works

A fence 2 feet high with openings no bigger than 1 inch, buried 3 to 6 inches or bent outward at the base. Chicken wire is enough, and it only has to guard the beds they like.
Cylinders of hardware cloth around the trunks of young trees and shrubs, tall enough to clear the winter snow.
Cages and cloches over lettuce and young seedlings until they are well past the tender stage.
Cutting back brush piles and tall cover nearby so they feel exposed.

Squirrels and chipmunks

The tellBulbs dug up overnight, holes the size of a fist, and tulip stems snipped.

Reading the damageBulbs gone, holes the size of a fist. Squirrels and chipmunks, digging. Skunks and raccoons dig wider, shallow patches in the lawn, usually for grubs, and can roll sod back like a carpet.

Myths

Planting daffodils among the tulips to protect them. Daffodils are untouched because they are bitter, but the tulips beside them are not safer for it.
Bone meal in the planting hole. The smell invites digging, and bulbs rarely need it.

What works

Laying chicken wire or hardware cloth on top of the bulbs after planting, pinned down, with mulch over it. Plants grow through the holes in spring.
Planting bulbs a little deeper, and firming and watering the soil so the ground does not smell freshly dug.
Choosing bulbs they avoid: daffodils, alliums, fritillaria, snowdrops, and scilla.
At the bird feeder, safflower seed, or seed treated with capsaicin, which birds cannot taste and mammals can.

Voles

The tellGnawed bark at the base of trees, runways in the grass, and 1-inch holes, usually under snow.

Reading the damageBark gnawed in irregular patches near the ground. Voles, usually under mulch or snow. The gnawing is small and scattered, often girdling the trunk, and there are 1-inch holes and worn runways in the grass nearby.

Myths

Planting daffodils or castor beans to keep them out. Neither does it, and castor beans are very poisonous.
Poison baits left in the open. They can kill pets and the hawks and owls that eat the voles.

What works

A cylinder of quarter-inch hardware cloth around each trunk, buried about 6 inches and standing at least a foot above the snow line.
Pulling mulch back a few inches from every trunk, so voles cannot nest against the bark.
Mowing the grass short in fall and clearing the dense cover and weeds they hide in.
Leaving perches and nest sites for owls and hawks, and not trapping the foxes and snakes that eat voles.

Moles

The tellRaised ridges and volcano mounds, with no gnawed plants.

Reading the damageRaised ridges across the lawn. Moles, hunting for earthworms and insects. The plants above wilt because the tunnel has cut under their roots, but the mole did not eat them. A tunnel with a mound of fine soil on top is a mole; small, tidy holes are voles or chipmunks.

Myths

Killing the grubs to get rid of moles. Moles eat mostly earthworms, so a grub treatment leaves them where they are and kills things you did not mean to.
Castor-oil repellents, sonic spikes, windmills, and chewing gum. None has held up in testing.

What works

Setting a harpoon or scissor trap in an active run. Press a section of the tunnel flat and set the trap where it is raised again by the next day.
Tolerating them in the lawn where you can. They aerate the soil and eat grubs and slugs, and a lawn mound pushes flat with a boot.
Burying 1/2-inch hardware cloth about two feet deep around a small raised bed or a prized bed, bent outward at the bottom.

Groundhogs

The tellA large burrow entrance with a pile of fresh earth, and whole vegetable plants gone.

Myths

Ammonia-soaked rags or sprinkled pepper at the burrow. Any effect lasts a day or two, and the fumes are not safe for you either.
Filling the burrow in. They dig another, and a burrow with a nursing mother inside leaves orphans.

What works

A fence 3 to 4 feet high with the bottom buried a foot deep and bent outward in an L, and the top foot left loose so it flops when they climb.
Fencing the vegetable garden rather than trying to move the animal.
Live traps where local rules allow it, checked often, since relocation is restricted in many places.

Birds

The tellPecked fruit, seedlings pulled, and berries gone in a week.

Myths

Plastic owls, rubber snakes, and scarecrows. Birds learn they are fake in days.
Shiny CDs. Moving tape does scare birds for a short time and that is all.

What works

Netting held on a frame above the crop, with mesh under 1/2 inch so birds and snakes do not get tangled, and the edges tied down. Draped netting traps wildlife and gets eaten through.
Floating row cover over seedlings and small plantings.
Planting a cheaper decoy crop, such as mulberries, away from the fruit you want to keep.

Keeping birds off fruit

Insects

Most of them aren't the problem

Only a small share of the insects in a garden damage plants, and many of the rest are eating the ones that do. Hand-picking, barriers, and patience cover most cases before anything is sprayed.

Slugs and snails

The tellHoles in leaves and silvery trails, mostly on hostas, lettuce, and seedlings, after a wet night.

Reading the damageHoles in leaf middles and silvery trails. Slugs and snails, feeding at night. The holes have smooth edges, and the slime trail dries to a shiny streak you can see in the morning.

Myths

Eggshell and coffee-ground barriers. Slugs cross them, and the evidence for either is thin.
Beer traps as a cure. They catch slugs, but the smell draws more in from the neighbouring gardens.
Diatomaceous earth around plants. It stops working when wet, and it harms the bees and beneficial beetles that touch it.

What works

Laying boards, flat pots, or melon rinds and emptying them each morning, since slugs shelter under them in the daytime.
Collecting at night with a flashlight and dropping them into soapy water.
Iron-phosphate baits, which are far safer around pets and wildlife than metaldehyde products.
Watering in the morning so the soil surface is dry at night, and keeping the mulch thin near the plants they love.
Copper tape around pots, which holds up better than anything else on a container.

Aphids

The tellClusters on new growth, sticky honeydew, curled leaf tips, and ants on the stem.

Reading the damageClusters on new growth, sticky leaves, curled tips. Aphids. The stickiness is honeydew, and ants walking up the stem are a sign they are farming them.

Myths

Buying ladybugs. Most fly away within a day or two, and many are wild-collected.
Buying praying mantis egg cases. Mantises eat anything that moves, including the bees and the predators you want.

What works

A hard stream of water, repeated for a few days, which knocks them off and they rarely get back on.
Insecticidal soap sprayed directly on the colony, in the evening or on a cool, cloudy morning.
Waiting a week. Hoverflies, lacewings, and native ladybugs arrive on their own if there are flowers nearby, such as alyssum, dill, and yarrow.
Cutting off badly infested tips and holding back on nitrogen, which makes the soft growth aphids love.
Keeping ants off the plant with a sticky barrier on the trunk, since ants protect the colony.

Japanese beetles

The tellMetallic green and copper beetles feeding in groups, leaving leaves skeletonised.

Reading the damageLeaves skeletonised, veins left behind. Japanese beetles, glossy green and copper, feeding in groups in the sun. Hundreds of tiny shot holes in young leaves are flea beetles.

Myths

Pheromone traps. They pull in more beetles than they catch, and a trap near your roses is an invitation.
Milky spore as a quick fix. It works only on this one grub, takes years to build up, and does poorly in cold soil.

What works

Knocking them into a jar of soapy water in the cool of the morning, when they are slow.
Row cover on small, prized plants through the beetle weeks, or simply accepting the damage. Established plants regrow.
Beneficial nematodes against the grubs in late summer, if you have counted enough to justify it.
Where you use a trap at all, hang it well away from the garden.

Caterpillars and hornworms

The tellLeaves chewed from the edge, with dark droppings below. On tomatoes, bare stems and a large green caterpillar.

Reading the damageLeaves chewed from the edges, black droppings. Caterpillars. The dark pellets on the leaf below are the giveaway, and the culprit is often well camouflaged. Check the underside, and the stem on tomatoes.

Myths

A sprinkling of cornmeal or flour to make them explode. They do not.

What works

Hand-picking. Look for the droppings, then follow them up.
Bt (Bacillus thuringiensis var. kurstaki), a bacterium that only affects caterpillars, applied to young ones and reapplied after rain. It kills the ones you want too, so never use it on milkweed, parsley, dill, fennel, or other host plants for butterflies.
Leaving hornworms that are covered in white rice-like cocoons, which are the larvae of parasitic wasps that will kill the next generation.
Planting extra parsley and dill so swallowtails have their share.

Squash vine borers and cucumber beetles

The tellA squash vine that wilts overnight with sawdust-like droppings at the base, or yellow-striped beetles on young cucumbers.

Myths

Spraying after the plant has wilted. The borer is already inside the stem.

What works

Row cover from planting until flowers open, edges buried.
Planting a second batch later in the season, after the borers' flight is over.
Mounding soil over leaf nodes so the vine roots in, and slitting an affected stem lengthwise to remove the borer and burying the cut.
Removing and bagging the vines at the end of the season so the pupae do not overwinter.

Lawn grubs

The tellBrown patches that lift like a carpet, with C-shaped white grubs underneath, and skunks or raccoons digging at night.

Myths

That any grub means treatment. A healthy lawn carries five to ten grubs a square foot without harm.
That killing grubs will end the digging. Skunks, raccoons, and crows come for what is there, and will move to the neighbour's if you clear yours.

What works

Cutting a square foot of sod in late summer and counting. Treat only if you find more than about ten.
Beneficial nematodes applied in late summer to warm, damp soil and kept watered.
Mowing a little higher and watering deeply, but less often, so adult beetles prefer another lawn.

Fungus gnats and mosquitoes

The tellSmall black flies rising from houseplant soil, or mosquitoes breeding in standing water.

Myths

Bug zappers. They kill mostly harmless insects and moths, and very few mosquitoes.
Citronella plants. The plant does not repel anything beyond an arm's reach, and a candle only works while it burns.
Ultrasonic mosquito repellers. They do nothing.

What works

Letting the top inch or two of houseplant soil dry between waterings, since the larvae need wet soil.
Yellow sticky cards to catch adults, and a layer of sand or grit on the soil surface.
Bti (Bacillus thuringiensis var. israelensis), soaked from mosquito dunks into the watering can for gnat larvae, or floated in standing water. It is harmless to bees, birds, and pets.
Emptying saucers, buckets, and gutters weekly so the larvae never finish.

The insect library A lawn that feeds pollinators

Fungal Disease

Prevention, because fungicides don't cure

Fungicides protect healthy leaves and do nothing for infected ones, so the work is spacing, airflow, dry leaves, and clearing the debris the spores overwinter in. Most of the fungus in a bed is harmless or helpful, and only the disease needs acting on.

Powdery mildew

The tellWhite powder on leaf surfaces, on phlox, bee balm, lilac, squash, and roses, in warm days and cool nights.

Reading the damageWhite powder on the leaf surface. Powdery mildew. It wipes off a little, favours crowded plants with warm days and cool nights, and is mostly cosmetic.

Myths

That baking soda alone cures it. It has some preventive effect and can burn leaves in sun or at strength.
That a fungicide clears an infected leaf. Sprays protect new growth. Mildew already on a leaf stays there.
That it kills the plant. On most perennials it is cosmetic late in the season.

What works

Giving plants sun and airflow. Space them out, thin the crowded centres, and pick resistant cultivars.
Preventive sprays started at the first sign and renewed every one to two weeks: sulfur, potassium bicarbonate, or horticultural oil. Do not use sulfur and oil together, or in hot weather.
Diluted milk spray, which has research behind it on squash and cucumbers, and works as a preventive, not a cure.
Letting it go on plants that are finishing anyway.

Black spot

The tellBlack spots with feathery edges on rose leaves, yellowing, and leaves dropping from the bottom of the plant.

Reading the damageBlack spots with fringed edges, yellowing, leaf drop. Black spot, mostly on roses. It starts low on the plant and moves up, spread by splashing water.

Myths

That it kills the rose outright. It weakens one that is defoliated year after year.
That a home mix of baking soda and soap is a reliable treatment. The evidence for it is weak.

What works

Raking up and bagging every fallen leaf in fall, and cutting out spotted canes in late winter.
Water at the base in the morning so leaves are dry by evening, and give each plant room.
Choosing resistant roses. This is the largest single change you can make.
Where you use a fungicide, starting at leaf-out and renewing every one to two weeks in wet weather, rather than after the spots appear.

Damping off

The tellSeedlings pinched and collapsed at the soil line, spreading across a tray.

Reading the damageSeedlings pinched at the soil line and falling over. Damping off. The stem is thin and water-soaked at the base, and it spreads across a tray in a day or two.

Myths

That cinnamon or chamomile tea prevents it. Neither does much, and they are no substitute for clean mix and good air.
That you can replant in the same soil. The organisms are still in it.

What works

Sterile seed-starting mix and trays washed before use.
Watering from below and letting the surface dry between waterings.
A small fan across the seedlings for part of each day, and sowing thinly.
Pulling out affected seedlings at once and bagging the soil.

Root rot and soggy-soil decline

The tellA plant that wilts while the soil is wet, with brown, mushy roots and a sour smell.

Myths

That more water fixes a wilted plant. In wet soil, wilting means the roots have died.
That a hydrogen-peroxide drench cures it. The effect is brief and also hits the beneficial organisms.
That a fungicide fixes bad drainage. It does not, and the rot comes back.

What works

Checking soil moisture two inches down before watering.
Fixing drainage before planting, or planting on a mound or in a raised bed. Our bed-prep guide covers the hole test.
Planting at the right depth, with mulch kept off the crown of the plant.
Choosing a plant that likes wet feet if the spot is always wet.

Tomato leaf spots and late blight

The tellSpots with rings on lower tomato leaves, or greasy grey-green patches with white fuzz underneath in cool, wet weather.

Myths

That diseased plants can go in the backyard compost. Most home piles do not get hot enough to kill the spores.
That a spray will save a plant with late blight. It spreads in days, and the affected plants and any nearby potatoes should come out and be bagged.

What works

Mulching to stop soil splash, staking, and pruning off the lowest foot of leaves.
Watering at the base in the morning, never overhead.
Rotating tomatoes and potatoes to a new bed every three years.
Removing early leaf-spot leaves at the first sign and bagging them. Our tomato guide goes further.

Browse the fungi Telling normal fungus from harmful Rose care and black spot Growing tomatoes

The Scorecard

Myth

Fleeting, and it harms the soil organisms that protect roots. The cause is drainage.

Composting diseased plants

Myth

A backyard pile seldom stays hot enough to kill spores. Bag it, or use a municipal hot compost.

Whatever You Use

Rules that apply to every remedy

Natural does not mean harmless. The same few habits keep you, your pets, and the pollinators out of trouble.

Read the label as the law

Rate, timing, target plant, and waiting period before harvest are all legal requirements, not suggestions. A homemade or organic product is not exempt from causing harm: copper accumulates in soil and harms worms, and sulfur and oil can burn leaves.

Mind the bees

Spray in the evening, when bees are in the hive, and never on open flowers. Soap, oil, neem, and spinosad harm bees on contact while wet, and most are safe once dry.

Test on one leaf

Spray a single leaf and wait a day before treating the plant. Leaves burn in heat, in full sun, or on stressed plants, and some plants, such as ferns and some herbs, are sensitive to soaps and oils.

Keep tools clean

Wipe pruners with rubbing alcohol between plants when working on anything diseased. Bleach corrodes the blades, and alcohol does the job.

Protect pets and children

Store baits and sprays out of reach. Some snail baits, rodent baits, and slug pellets are poisonous to dogs, and poisoned rodents poison the owls and hawks that eat them.

Looking for something?

Let us know and we will add it to the list for your garden plan.