Alfalfa

Worth knowing before you sow, not after a failed reseeding.

Newly sown alfalfa germinating patchily or not at all in ground that grew alfalfa within the last year. Seedlings that come up, stall at the first true leaves, and sit there without ever taking off. Stunted, forked, or branched taproots on the few plants that do establish, instead of one straight deep root. Overseeded seed disappearing into a thinning stand with no visible improvement the following season. Damage worst in the top few inches of soil and heaviest immediately around old crowns and where residue was tilled in.

There is nothing to apply and nothing to rescue once seedlings have been checked - the plants that emerged stunted will not catch up, so the honest answer is to accept the loss and re-sow the following year after a season of something else. If you must have alfalfa on that ground sooner, deep tillage and thorough irrigation to leach the top few inches shorten the wait, but a full year with another crop is what actually works.

Do not sow alfalfa into ground that has grown alfalfa within the past twelve months, and do not try to thicken an established stand by overseeding it - neither will work. Plan the rotation instead: take one full season of a different crop, ideally a grass or a cereal that will also use up the nitrogen the old stand left behind, then reseed. Where an old stand is being turned under, tilling and irrigation both help by breaking up and leaching the residue, so a wetter climate clears faster than a dry one. If a stand thins early, the productive move is to overseed it with a grass or clover rather than with more alfalfa.

Alfalfa releases water-soluble compounds - medicarpin and related saponins - from its roots and decaying residue that specifically suppress the germination and root growth of alfalfa seedlings. It is a well-documented effect rather than garden folklore, and it explains two failures that otherwise make no sense: overseeding a thinning stand to thicken it does nothing, and reseeding a bed right after turning an old stand under produces stunted plants that never establish a proper taproot. The effect is strongest in the top few inches of soil, is worse on heavy soils and in dry conditions where the compounds are not leached away, and it lasts roughly a year. Seedlings under about a year old do not yet produce enough to poison their neighbours, so a young stand can be thickened; an established one cannot.

Fence it, or plant it accepting that you are feeding deer.

Growth cleanly missing overnight, with the plant browsed back to a level line about as high as a deer can comfortably reach. Ragged, torn stem ends rather than the clean angled cut a rabbit leaves - the single most reliable identifier. Buds and flowers gone while the foliage below is untouched, since deer often take the best part first. Hoof prints and droppings in soft ground near the damage. Repeat visits, with fresh damage each morning once a planting has been found. On young trees, shredded and stripped bark and broken low branches in autumn - that is antler rubbing rather than feeding.

There is no chemical fix, only exclusion and recovery. Get physical protection up immediately after the first damage, because deer return to a known meal, and reinforce or rotate whatever you were relying on before. Most plants regrow from browsing if the crown and roots are intact - feed and water a grazed plant and protect the regrowth while it comes back. What does not recover in the same season is anything whose buds or flowers have been taken, and a young tree whose bark has been rubbed right around the trunk is usually lost. Where deer pressure is genuinely heavy, the honest answer is to fence properly or to grow the plants deer leave alone, rather than to keep replacing losses.

Fencing is the only thing that reliably works. Eight feet is the standard for excluding deer, or two parallel four-foot fences a few feet apart, which they will not jump because they cannot judge the landing. Short of that, cage individual plants: a sturdy wire cage or trunk guard around every young tree, left on until the trunk is thick and the canopy is above browse height, prevents both browsing and antler rubbing and is the single highest-value thing you can do for a young tree. Repellent sprays do help at moderate pressure, but they wash off and deer habituate, so reapply after rain and rotate between different types through the season. Motion-activated sprinklers, scent deterrents, and noise devices work for a while and then stop. Siting matters too: plants close to the house, in daily traffic, and screened behind other planting get browsed less than the same plant out at the boundary.

Deer are the largest garden problem across much of the country, and where pressure is high they set the limit on what you can grow at all. They browse at night and around dawn and dusk, taking tender shoots, leaves, buds, flowers, and fruit within about five feet of the ground, and they come back night after night to anything they have found and liked. Because they have no upper incisors they tear rather than cut, leaving ragged stem ends - that is how you tell deer damage from a rabbit's clean angled cut. In fall, bucks rub their antlers on young trunks and can strip the bark right around a stem, which kills a young tree outright. Palatability varies enormously between plants and between seasons: a herd short of food in late winter eats things it ignores in June, and no plant is truly deer-proof.

Sharp drainage and stopping cuts four to six weeks before frost are the two things that prevent it.

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.

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.

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.

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.

If regrowth after the second cut goes yellow at the leaf tips, this is why - cut early next time, or switch to a glandular-haired variety.

A distinct V-shaped or wedge-shaped yellow patch running from the leaf tip back toward the middle - the signature, and quite different from the general paling of a nitrogen shortage. Leaves later turning red or purple, curling, and dropping. Stunted, shortened stems and a stand that simply refuses to grow after a cut. Tiny bright green wedge-shaped insects that run sideways and hop or fly when you sweep a hand across the top of the stand. Damage worst on the second and third growths of summer and heaviest on new seedings.

There is no way to reverse hopperburn on a leaf that already shows it, so the response is to cut the stand and let the regrowth start clean. Check the new growth after cutting, because migrating adults move straight onto it. Insecticides labeled for alfalfa are used against threshold populations on a field scale but are seldom warranted in a garden; the leafhopper is also highly mobile, so a sprayed patch is quickly recolonized from surrounding vegetation.

The practical home control is timing and variety. Cutting early, at bud stage, removes the population with the crop and gives the regrowth a clean start. Glandular-haired resistant varieties are genuinely effective - the sticky hairs deter the insect - and are worth choosing outright if leafhopper is a recurring problem in your area, though they take a season longer to express full resistance. Avoid stressing a stand, since a vigorous plant tolerates more feeding, and do not rely on beneficial insects, which do not suppress this pest well.

A tiny, wedge-shaped, bright lime-green insect that migrates north on storm fronts each summer and feeds by injecting saliva into the leaf veins. It is not the tissue loss that hurts but the toxin: the plant's vascular system is disrupted, and the leaves develop a distinctive V-shaped yellow wedge from the tip inward - 'hopperburn' - before turning red or purple and dropping. Growth stunts, stems shorten, and both protein content and yield fall sharply. Because the damage appears one to two weeks after the feeding that caused it, by the time a stand looks yellow the harm is already done. It hits the second and third cuttings hardest, and new seedings worst of all, and it feeds on beans, potatoes, and many other crops besides alfalfa.