Camellia

Set the top of the root ball an inch or two ABOVE grade, mound soil up to meet it, and never let the trunk flare be buried or mulched over. Heavy clay and a low spot are both fatal - build a raised bed instead. A shrub that wilts, yellows and dies back on one side in wet ground is telling you this.

Wilting in the middle of the day on a plant whose soil is damp - the classic tell, and the reason people water a rotting plant and finish it off. Leaves yellowing from the bottom up, dull off-color foliage, and growth that stalls for no visible reason. Whole shoots, or one side of the plant, collapsing while the rest still looks fine. Soft, dark, or mushy tissue at the base of the stem or at the crown, sometimes with a sour smell. Lift a failing plant and look at the roots: healthy ones are firm and pale, rotted ones are brown or black and slimy, and the outer layer slips off between your fingers leaving a thread of core behind. Seedlings that topple over at soil level are the same problem, called damping-off.

There is no cure for tissue that has already rotted, so act on the conditions rather than looking for a spray. Stop watering at once and fix the drainage - open up compacted soil, or move the plant to a raised, sharply drained position or a container. Lift a badly affected plant, cut away every soft dark root and rotted section with a clean blade back to firm pale tissue, and replant only the healthy parts into fresh free-draining soil or mix. Often the better move is to give up on the plant and save its offspring instead: cuttings, offsets, or divisions taken from firm healthy growth root readily and give you a clean start. Bin the rotted material rather than composting it, and correct the drainage before you replant, because the rot comes straight back in the same wet spot.

Drainage is the whole defense. Match the plant to the site first - something that wants sharp drainage will not survive heavy clay or a low, water-collecting spot however well you tend it. Where the ground is heavy, plant on a raised bed, berm, or slope, or grow in a container. Set plants at the depth they were already growing, since burying the crown or the root flare is a common cause of rot, and keep mulch pulled back a few inches from the stem base instead of piled against it. Water the soil rather than the calendar: check that the top inch or two is dry before watering again, cut back hard in cool weather and winter dormancy, and never leave a pot standing in a full saucer. Do not plant or dig in soggy ground, and go easy on rich amendments for plants that want it lean. Rotate annual crops, and start with clean healthy plants and fresh mix.

Root rot is not one organism but a group of soil fungi and water molds - Pythium, Phytophthora, Fusarium, Rhizoctonia and others - that sit harmlessly in most soils and only turn destructive when the ground stays saturated. Waterlogged soil drives the air out, the roots suffocate, and the weakened tissue is invaded and goes soft, brown, and stringy. Because the damage is underground you usually see it first as something that looks like drought: wilting, yellowing, stunting, a plant that does not respond to being watered. Overwatering, heavy compacted ground, a low spot that collects runoff, a pot with no drainage or a saucer left standing full, and cold wet soil in winter are the usual causes. Once roots have actually rotted there is no cure - this is a problem you prevent rather than treat.

It packs the leaf UNDERSIDES with white and brown specks, so the first thing most people see is yellow mottling on the upper surface and sooty black film on the leaves below. Turn a mottled leaf over before doing anything else. Thorough oil coverage of the undersides timed to the crawlers, plus thinning the shrub for light and air, is the control; a badly encrusted interior branch is better pruned out.

Rows of small brown, tan, black, white, or waxy bumps along stems, twigs, leaf midribs, and leaf undersides that do not brush off but can be scraped loose with a fingernail. A sticky shine on the leaves - and on the floor, table, or path beneath the plant - that later turns black with sooty mold. Ants running steadily up and down the stems, since they farm and defend scale for that honeydew; often the first sign anything is wrong. Yellowing leaves, weak thin growth, and dieback of individual branches or canes that are heavily encrusted. On fruit crops, scale covers and sooty mold directly on the fruit. Check the leaf undersides and the shaded inner wood, which is where colonies build up unseen.

Horticultural oil is the main control: it works by smothering, so it has to coat the insects thoroughly - stems, twigs, and leaf undersides - and it usually needs repeating, because the waxy covering shields them and no single pass reaches everything. On deciduous woody plants a dormant-season oil smothers the overwintering stage while the leaves are out of the way, and timing a growing-season spray to the crawler stage, when the young are mobile and uncovered, is far more effective than spraying settled adults. On a small plant or a light infestation, scrub or wipe the scales off by hand, or dab them with a cotton swab of rubbing alcohol. Prune out and destroy badly encrusted wood rather than trying to save it. Wash off the sooty mold once the scale is gone - it lives on the honeydew, not on the plant, and stops once the supply does. Anything you spray must be labeled for the plant, and oils can burn delicate foliage, so test first.

Inspect. Look over leaf undersides and stems regularly - on a crop you pick, every harvest is a scouting chance - and check every new plant thoroughly before you buy it, plant it, or set it beside anything else, because scale almost always arrives on a plant rather than flying in. Quarantine new houseplants for a few weeks. Keep plants unstressed and not over-fertilized, since soft, forced growth is what populations build on. Prune for airflow and light to open up the shaded inner growth where scale hides, and prune out heavily infested wood as routine maintenance - on anything that gets a hard annual pruning, that alone removes most of any buildup. Leave the lady beetles, lacewings, and parasitic wasps alone, since they normally keep scale down to nothing, and keep ants off the plant where you can, because ants protect the colonies from those predators. Indoors, avoid hot, dry, still winter air.

Scale insects are sap-suckers that spend most of their lives immobile, fixed to a stem, twig, or leaf underside beneath a waxy or shell-like cover. They look far more like bumps, blisters, or crusty encrustations than like insects, which is why an infestation is usually well established before anyone notices it. Soft scales excrete large amounts of sticky honeydew that drips onto everything below and grows a black sooty mold - and those blackened leaves are often the first thing a gardener actually sees. Armored scales produce no honeydew but sit under a hard shield that protects them from most sprays. They spread as tiny mobile crawlers in the weeks after hatching, which is the only stage that moves and the only stage that is easy to kill. Populations build on stressed plants, on crowded shaded growth, and above all on plants kept indoors in dry, still air over winter.

Japonicas suffer most because they hold their spent flowers; sasanquas shatter and escape much of it. The disease never harms the shrub, only the display.

Brown blotches spreading from the base of the flower outward, with the petal veins staying darker than the tissue between them - unlike frost, which browns the outer petal edges first and hits only the blooms that were open during the freeze. Flowers going leathery brown and dropping whole within a day or two of opening. A ring of collapsed brown blooms on the ground under the shrub. Small hard black lumps about the size of a lentil in last year's fallen flowers and in the litter underneath. Bloom after bloom affected while the leaves, stems and buds stay entirely healthy - that is the signature of this disease and rules out root or scale problems.

No spray cures an infected flower, and fungicide programs are impractical at home - the blooms open over months and each one would need protecting individually. What works is relentless removal: strip and bin blighted blooms as they appear, keep the ground under the shrub clear, and refresh the mulch every autumn. Do not move soil, mulch or fallen flowers from an affected shrub to another part of the garden, and do not give away rooted cuttings in that soil. Expect improvement over several seasons rather than a fix in one, and understand that where the disease is widespread, spores blowing in from neighboring gardens make this something you manage rather than eliminate.

Sanitation is the whole defense. Pick up every fallen flower every few days through the entire bloom season and bin or burn them - never compost them and never leave them lying under the shrub, because that is precisely where next year's infection is made. Pick the spent flowers off the plant too, since japonicas hold on to them. Each fall, rake off and replace the top few inches of mulch and litter, then mulch 3 to 4 inches deep, which buries any sclerotia too far down to shoot. Avoid overhead watering while the shrub is in bloom. Sasanquas, which flower earlier and shatter their petals, escape much of the damage, so they are the better choice in a badly affected garden. Inspect any new camellia and remove its flowers and the surface of its potting mix before planting.

Camellia petal blight is caused by the fungus Ciborinia camelliae, and it attacks the flowers only - the shrub itself stays perfectly healthy while every bloom rots. Small brown specks appear on the petals and enlarge into blotches that spread from the base of the flower outward, until the whole bloom goes leathery brown and drops, often within a day or two of opening. The petal veins stay noticeably darker than the tissue between them, which is what separates blight from ordinary freeze damage. The fungus overwinters as hard black bodies called sclerotia in the fallen flowers and the top inch of soil under the bush, and releases its spores in late winter and spring, exactly when the flowers open. It travels on the wind and arrives in bought plants, and once it is loose in a garden it is very difficult to be rid of.