Roman Chamomile

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.

Watch for: 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.

Prevent: 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.

Treat: 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.

Cold, wet winter soil is the single most common way an established Roman chamomile mat is lost - far more often than cold itself. Plant into light, sharply drained ground or raise the bed, never a low spot that puddles, and if the centre goes soft, take divisions from the firm outer edge and replant elsewhere.

A chamomile lawn is not a grass lawn. Roman chamomile takes light, occasional foot traffic - a path you cross, a seat you sit on, a bank you walk over now and then - but it does not tolerate the daily wear grass shrugs off, and the old saying that chamomile grows stronger the more it is trodden is charming rather than true. Concentrated traffic crushes the low crowns and shears the shallow roots; the mat thins, opens to bare soil, and weeds move into the gaps faster than the chamomile can close them. Damage is worst in the first year before the planting has knit together, on ground that is wet or frozen, and along the one line everybody actually walks. It is a wear problem rather than a disease, so nothing you spray will fix it.

Watch for: Thin, flattened, or bald patches following the line people actually walk. Bare soil showing through a mat that used to be closed, with weeds germinating in the openings. Crowns crushed flat and slow to spring back after being stepped on. Damage that appears after the planting was used while wet, frozen, or newly planted. Wear concentrated at gateways, corners, and around seats and stepping stones, while the rest of the mat stays dense.

Prevent: Give a new planting a full season with no traffic at all before you walk on it. Site it where the walking is light and occasional rather than daily, and set stepping stones into the line people actually take so the chamomile grows around them instead of under them. Keep off it when the ground is wet, frozen, or in winter dormancy. Plant close - 4 to 6 inches apart for a lawn - into weed-free, free-draining ground so the mat closes quickly and stays dense, and shear or mow it high a few times a season to keep it thick. Above all, plan it as a small fragrant feature rather than a play surface.

Treat: Take the traffic off the worn area first, or nothing else will hold. Loosen the surface, weed the openings by hand, then plug the bare patches with rooted pieces split from a dense part of the mat, firm them in and keep them watered until they knit - spring and early autumn are the best times for it. Never reach for a lawn weedkiller on the weeds that moved in: the selective products that spare grass kill chamomile just as thoroughly. If the same line wears bare every year, move the path rather than replanting it again.

The most common disappointment with a chamomile lawn, and it is worth knowing before you plant: a fragrant surface for light use, not a replacement for grass.

An established Roman chamomile mat thins for two ordinary reasons, neither of them an infection. In hot, humid summers the dense low canopy holds moisture against the ground, the interior browns out, and patches go crisp or slumped until cooler nights let it recover. And with age the planting simply runs outward: the crowns at the centre grow woody and sparse while the vigorous growth moves to the edges, so a mat that was solid in year two can look bald in the middle by year four. Both look alarming and neither needs a spray. What turns them into real losses is rich soil, heavy shade, or ground that stays wet, all of which keep the interior soft and slow to recover.

Watch for: Browning, crisping, or a flattened slumped patch in the middle of an otherwise healthy mat during a humid heat wave. A ring of vigorous growth around the edges with a woody, sparse, bare centre - the classic sign of an ageing planting. Growth that no longer releases much apple scent when brushed. Patches that stay dark and wet for days after rain. Soft, floppy, thin growth in shade or in soil that has been fed.

Prevent: Grow it lean, sunny, and sharply drained - poor to average soil, full sun to light shade, and ground that never puddles. Skip the fertilizer, since feeding produces soft growth that mats down and rots from the middle. Shear the planting after bloom so air moves through it rather than letting the growth pile up. Divide every two or three years, before the centre goes woody, replanting the young rooted pieces taken from the outer edge. In humid climates give it an open position with air movement, and water in the morning at soil level rather than over the top of the mat.

Treat: Shear the affected area back and let it regrow; a mat cut over in late summer usually comes back clean once the nights cool. Rake out the dead material so light and air reach the crowns. Where the centre has gone woody and bare, lift the whole planting, pull it apart, discard the old woody core, and replant the vigorous rooted pieces about 6 inches apart into loosened soil - a renewed mat closes again in one season. Improve the drainage before replanting if the patch stayed wet.

Expect to renew a Roman chamomile planting by division every few years. It is routine maintenance for this plant, not a failure.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Watch for: Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Prevent: Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Treat: Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

They gather on the soft spring flush and on flower stems, and a mat this dense hides them - part the foliage to check. A light shear plus the hoverflies and lacewings that the open flowers recruit usually settles it without any spray.

Powdery mildew is a fungal disease that coats leaves - and often stems, buds, and fruit - in a white-to-gray powder that looks like spilled talcum. It is not one fungus but a large family of them, each fairly specialised to its own group of plants, which is why mildew on one crop rarely jumps to an unrelated one beside it. Unlike most leaf diseases it does not need wet leaves: it thrives on warm dry days followed by humid nights, and it takes hold fastest where plants stand crowded in still air or in shade. The coating blocks light, so heavily covered leaves yellow, brown, and drop early. On many plants that is mostly disfiguring and arrives late enough not to matter; where it strips away the leaves a crop still needed to finish, it costs you size, sweetness, and quality.

Watch for: Round white powdery spots on the upper leaf surfaces that spread and merge until whole leaves look dusted. It usually starts on the oldest, lowest, most shaded leaves and works upward, so check there first. Look at the undersides too, and at stems, buds, and flower stalks, which get coated as it advances. Leaves that yellow, brown, curl, or go crisp and drop early under the coating. New growth that opens small, crumpled, or twisted where the fungus has reached the shoot tips. On plants where it gets onto the fruit, a dull gray film, russeted or scarred skin, and cracking. Late in the season, tiny dark specks scattered through the white felt - that is the fungus setting up to overwinter on the debris.

Prevent: Give plants room. Crowding and still air are the biggest single driver, so space at the full recommended distance, thin seedlings properly, and divide or prune out congested growth until air moves through the plant. Full sun and an open position help; deep shade and a still corner against a wall are where it always starts. Water at the base rather than overhead, and water early in the day so nothing stays damp overnight. Keep plants evenly watered - drought stress at the roots leaves them far more susceptible, even though the fungus itself likes dry air. Go easy on nitrogen, since soft lush growth is the most vulnerable. Where resistant varieties exist for what you are growing, choosing one is the single most effective thing you can do on a plant that mildews every year. Clear infected leaves and stems away at the end of the season rather than composting them.

Treat: Start early: sprays protect healthy tissue, they do not clean up leaves that are already coated. Pick off and bin the worst leaves as soon as you see them, and open the plant up by thinning or pruning so air moves through. On anything that regrows quickly, shearing the whole plant back forces a clean flush and beats spraying. If it keeps spreading, potassium bicarbonate, horticultural oil, or neem applied weekly will hold it - cover both leaf surfaces. Sulfur also works, but it burns the foliage of some plants, should never go on in heat, and must not be mixed with or applied close behind an oil spray. Whatever you use must be labeled for the plant you are treating: follow that label and observe its pre-harvest interval on anything you eat. Do not compost badly infected material. Late-season mildew on a plant that is finishing anyway is usually cosmetic; on a crop still filling out it is worth acting on.

A dense, unsheared mat in still, humid late-summer air is what mildews. Shear the patch back so air moves through it and the regrowth comes clean; dividing an overgrown planting prevents a repeat.