Culver's Root

Leaf scorch is not a disease and there is nothing to spray for it. It is what happens when a leaf loses water faster than the roots can replace it: the tissue farthest from the veins - the margins and the tips - dries out first and turns brown and papery, and the browning works inward while the rest of the leaf stays green. Hot sun, dry soil, drying wind, heat reflected off paving or a wall, a small or damaged root system, and a plant sited somewhere sunnier or drier than it wants are the usual causes, singly or together. It also happens in winter on evergreens, when bright sun and wind pull water out of the leaves while the ground is frozen and the roots cannot resupply. Shade and woodland plants, shallow-rooted plants, and anything recently planted scorch most easily.

Watch for: Browning that starts at the leaf edges and tips and spreads inward, with a fairly sharp line between the crisp brown tissue and the green that is still healthy. Leaves and fronds going dry, papery, and crisp rather than soft, yellow, or spotted - that is what separates this from a fungal problem. Damage worst on the side of the plant facing the sun or the prevailing wind and on the most exposed upper leaves, while the shaded interior stays fine. Symptoms appearing sharply after a heat wave, a dry spell, or a bright windy week in winter. Whole leaves or fronds shed early as the plant cuts its losses.

Prevent: Site the plant where it actually wants to be. This is a placement problem far more often than a watering problem, and a shade plant in hot afternoon sun will scorch every summer however much you water it. Give shade and woodland plants part-to-full shade and shelter from hot afternoon sun and drying wind. Keep the root zone consistently moist and mulch it well with leaf litter or another organic mulch, which holds water and keeps the roots cool - the single most useful routine step. Water deeply and thoroughly during dry spells rather than little and often, so moisture reaches the whole root zone. Pay particular attention through the first year after planting, when the root system is small and cannot keep up with the leaves. On evergreens in cold regions, make sure the plant goes into winter well watered, and keep it out of bright, windy, exposed positions.

Treat: Water deeply, mulch, and improve the shade - that is the whole treatment, because there is nothing here to kill. Leaves that are already scorched will not recover, so trim off badly browned foliage or fronds for appearance if you want to; the crown and roots are usually unharmed and push out fresh growth once conditions improve. On a plant that scorches badly every year the answer is to move it rather than to keep watering harder, because the siting is what is wrong. Some plants respond well to being cut back hard, which brings a clean flush of new foliage. And on plants that naturally die back or brown off late in the season, scorching at the end of a dry summer is normal and needs nothing at all.

Culver's root wants consistently moist, rich soil and is happiest in a rain garden or low spot. Give it some afternoon shade in hot climates; it rebounds with steady moisture.

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.

Cosmetic and rarely significant, arriving late in the season. Removing affected leaves and opening up crowded clumps is all it needs.

Crown rot is the rotting of a plant at the crown - the growing point where the stems meet the roots, right at or just below soil level. Soil fungi and water molds that live in most ground attack that tissue whenever it sits wet, cold, and airless, and because the crown is the one part a perennial cannot regrow from, losing it usually means losing the plant. It is above all a winter problem: a plant that survives hard frost perfectly well in dry ground rots out in a wet one, and the classic story is a perennial that simply never comes back in spring. Dry-adapted plants growing in heavy or over-improved soil are the most vulnerable, along with anything that has mulch, wet leaves, or piled debris sitting against the crown, and anything planted too deep.

Watch for: A plant that fails to green up or emerge in spring when everything around it does - the most common way this gets discovered, and by then it is already too late. Stems that wilt, blacken, and collapse in wet weather while the soil is clearly damp rather than dry. A crown that is soft, dark, brown, or mushy when you press or lift it, sometimes with a foul smell, instead of firm and pale. New growth that pulls away from the crown with almost no resistance. Clumps browning and going hollow in the middle while the outer growth stays alive. In stands and cover crops, patches wilting, yellowing, and thinning out after wet spells or over a mild wet winter.

Prevent: Drainage and airflow at the crown are everything. Match the plant to the site first: a dry-adapted perennial planted in heavy or enriched ground is on borrowed time whatever else you do. In wet or clay soil, plant on a slope, berm, raised bed, or gritty rock-garden site so water drains away from the crown rather than standing over it. Set plants at the right depth - never bury the crown - and keep mulch, dead leaves, and debris pulled back from it rather than piled against it, since damp material resting on the crown is a common trigger. Do not overwater, and ease right off during dormancy, when a resting plant wants to be barely damp rather than wet. Give crowded plantings enough space and airflow to dry out, and do not sow a stand too thickly. In cold, wet climates, divide in spring rather than fall, so plants are not recovering from surgery through the wettest months.

Treat: There is usually no cure once the crown itself has rotted: the plant is lost, and the job is to save what you can and fix the site. Lift it, cut away every soft, dark, rotted part with a clean blade back to firm tissue, and replant only healthy divisions or firm outer growth into fresh, sharply drained soil or medium. On potted and specialist plants, repotting into fresh airy medium and keeping them drier with better airflow gives the best chance, though a badly rotted crown is usually beyond saving. Bin the rotted material rather than composting it. Replant somewhere better drained rather than back into the same wet spot - or start again from seed, cuttings, or self-sown seedlings, which is the realistic option for anything that resents being moved at all.

Culver's root loves moist soil, so this is specifically about stagnant, waterlogged ground over winter - and particularly about mulch piled against the crown. Keep the crown clear and the soil moist rather than dead-wet.