Purple Top White Globe Turnip

Root crops are biennials that flower in their second year after winter cold. When spring-sown plants experience cold exposure (below 50°F for 1-4 weeks) during their juvenile stage, then warm days arrive, they may interpret the cold as 'winter complete' and flower in their first season instead of bulking up roots. Beets, chard, spinach, lettuce, radishes, and turnips have short vernalization requirements (1-4 weeks) — direct-seeded crops are most at risk. Carrots, parsnips, storage onions, and fall-set shallots need much longer vernalization periods, so they bolt less from spring cold. Once the plant commits to flowering, root development slows or stops.

Triggers: Per MSU Extension: beets, chard, spinach, radishes, turnips have 1-4 week vernalization requirements — direct-seeded plantings most at risk in cold springs. Carrots, parsnips, storage onions need 8-12 weeks vernalization, so rarely bolt from spring cold. Plants must have reached juvenile size threshold to be vernalization-susceptible.

Risk fades when: Once bolted, root development stops. Harvest whatever's usable. Fall sowings rarely bolt because plants don't reach vernalization-susceptible size before harvest.

Flea beetles are small (1/16-inch) shiny beetles that jump like fleas when disturbed. They chew small round 'shothole' or 'pinhole' damage in leaves and can destroy emerging cotyledons of broccoli or eggplant in 24 hours. Most species are host-family specific — crucifer flea beetle on brassicas, tuber flea beetle on potatoes, eggplant flea beetle on solanaceous crops.

Where it lives: Across the US

Triggers: Overwinter as adults in leaf litter and field margins. Active at mid- to late-spring temperatures. Warm winter → higher next-spring populations (NC State). Hot dry conditions amplify damage on stressed seedlings.

Risk fades when: UMN: 1-2 generations in Minnesota, populations crash after mid-June

Forked roots happen when a taproot hits a physical obstruction — a stone, hard clod, buried debris, compacted subsoil — and splits into two or more roots going around it. Common in heavy clay or rocky soils, especially when the bed wasn't loosened to a full 12-inch depth before sowing. Other contributors: excessive nitrogen fertilization pushes hairy lateral roots, transplanting damages the taproot, crowded sowing forces neighboring roots to twist together, and root-knot nematodes mimic the symptom. Prevention is in bed prep — loosen soil to 12 inches, remove stones larger than 1/2 inch, avoid fresh manure or heavy nitrogen the season of planting. Direct-seed rather than transplant. Thin seedlings to proper spacing.

Triggers: Per UMN/UIllinois Extension: forking from physical obstructions in soil (stones, clods, debris), compacted subsoil, excessive nitrogen, or crowded plantings. Root-knot nematode infestation causes a similar symptom but with visible galls.

Risk fades when: Affected roots are still edible but cosmetic. For next planting: deep-loosen bed 12 inches, sieve out stones, work in compost (not fresh manure or high-N), direct-seed not transplant, thin to proper spacing.

A carrot, parsnip or radish that comes out of the ground split lengthwise was not diseased and nothing chewed it. It grew too fast, too suddenly. When soil dries out, root growth slows and the skin firms up. Water it heavily, or let a downpour land on a dry bed, and the inner tissue swells faster than that hardened skin can stretch. The root ruptures. USU Extension is explicit about who this happens to: cracking occurs in older roots and is associated with poor irrigation practices. That word older is the key. Big, mature, large-rooted cultivars split; small young ones flex and survive the same weather. So the two levers are steady moisture and pulling the crop on time, and the longer a mature root sits in the ground the more rain events it has to survive. A cracked root is perfectly edible - trim the split, use it first - but it will not store, because the open crack lets soil and rot in. One quirk worth knowing: roots can also shatter at harvest if you dig them while they are very cold.

Triggers: USU Extension: cracking is a problem in carrot, parsnip, and radish; it occurs in older roots and is associated with poor irrigation practices. When irrigation is erratic, roots take in more water, the root expands quickly, and it may crack. Large-rooted cultivars, and older roots, are more prone to split than small young ones. Keeping soil moist for steady growth matters most in sandy or drought-sensitive soils. Splitting or shattering can also happen at harvest, particularly if the roots are very cold when dug. The same swelling mechanism applies to other storage roots that size up quickly, such as rutabaga and salsify, though extension sources name carrot, parsnip and radish specifically.

Risk fades when: A split root does not heal. Harvest it and use it first - cracked roots store poorly because the open crack admits soil and decay. Shallow surface splits can be peeled or trimmed away and the flesh beneath is sound. Prevention for the next sowing: irrigate to keep the soil evenly moist rather than letting it dry and then soaking it, mulch to buffer swings, pick smaller-rooted cultivars where cracking is chronic, and harvest promptly once roots reach size. Avoid digging roots when they are very cold, which can cause shattering at harvest.

Microscopic soil-dwelling roundworms that burrow into plant roots and cause swollen knots (galls). Above ground, the plant looks stunted, yellowed, and wilted even with plenty of water. They attack over 2,000 plant species, so almost nothing is safe. They're most active in warm soil (70-85°F) and do more damage in sandy soils, where they move easily. Once a bed has them, populations stick around for years.

Triggers: Soil temperatures of 70-85°F are ideal for them; below 60°F they go dormant. Sandy soils make it easy for them to move and reproduce, while heavy clay slows them down considerably. In warm soil, a full generation completes in about 27 days.

Risk fades when: Activity drops sharply once soil cools below 60°F. Damage stops accumulating for the season, but the population stays in the soil and returns when warmth does.

Slugs and snails are nocturnal mollusks that chew irregular holes in leaves and clip off succulent seedlings. They leave characteristic silvery slime trails. Hermaphroditic and prolific, brown garden snails lay around 80 eggs per month for up to six clutches per year.

Where it lives: Across the US, including watered gardens in the desert Southwest

Triggers: Active at night and early morning in damp conditions. Coastal CA and southeast — active year-round. Spring rains and dense ground cover (mulch, debris, weeds) create harborage.

Risk fades when: Hot, dry summer weather drives slugs and snails into inactivity, so risk drops sharply once conditions turn warm and dry; populations are highest in cool, wet spring and fall, and in mild-winter coastal regions they can stay active year-round (UMN Extension, Penn State, UC IPM).

Wireworms are the larvae of click beetles. They live in the soil, eating seeds, seedlings, roots and tubers, and they bore small holes and tunnels into potatoes and sweet potatoes that can make them unusable. For home-garden sweet potatoes, UGA Extension says wireworms and root-knot nematodes seem to be the biggest problems. Their main food is the roots of grasses, so the worst damage comes in gardens dug out of sod or lawn within the past few years. Some kinds take several years to grow up, so a problem bed can stay a problem for years. Severe outbreaks are rare, and once you see damage no spray will fix it: the steps that work are taken before planting.

Where it lives: Found across the US; different wireworm species are the main pests in different regions

Triggers: Larvae and adults spend the winter 9 to 24 inches deep in the soil. In spring, once the soil warms to about 50 F, larvae feed within the top 6 inches; when the soil gets too hot (above 80 F) or dry they go deeper, and as the soil cools in fall they may feed near the surface again. They like moist, cool, heavy soil. Female click beetles lay eggs in grassy, weedy areas, which is why ground that was sod or lawn has the most wireworms. How long one generation takes depends on the kind: from one to six years. The corn wireworm takes up to six years, so larvae of every size are in the soil at once. In the Southeast, the southern potato wireworm has one or two generations a year and the tobacco wireworm has one.

Risk fades when: Wireworms do most of their damage in early spring, when they are near the soil surface; in summer they move deeper, and as the soil cools they may feed near the surface again (NDSU Extension). They become active and look for food as soon as the soil warms in spring (UMass Extension). In the Southeast, wireworms usually attack potatoes and sweet potatoes late in the season (Clemson HGIC; NC State Extension). The month numbers are a reading of 'spring' and 'late season' for most of the US; spring comes earlier in the South and later in the North.

Turnips are a crop you harvest young. UMN Extension gives the size and the reason together: pull them at about two to three inches across, because as the roots become larger they are more likely to become bitter, strong-flavoured, woody or fibrous. Illinois Extension adds that quality is best when roots are medium-sized and have grown quickly and without interruption, and that old turnips tend to be tough and woody. Two things toughen a turnip. Leaving it in too long, which is easy to do because the shoulders sit above the soil and a big root looks like a better one. And slow, stressed growth - drought stress makes turnips and rutabagas bitter or woody, and heat does the same, because a turnip is a cool-season crop whose quality suffers when it matures in warm weather. The plants carry a large storage root on a root system that is not extensive, so an inch of water a week matters more than it looks like it should. Grow them fast, in cool weather, and pull them small.

Triggers: UMN Extension: harvest turnips at a usable size, normally about two to three inches in width; as roots become larger they are more likely to become bitter, strong-flavoured, woody or fibrous; quality can be poor when they grow in hot weather or if they grow too large; drought stress can make turnips and rutabagas bitter or woody; although the storage root is large, the plants do not have extensive root systems for absorbing water and need one inch of water per week. Illinois Extension: turnips are of best quality, mild and tender, when of medium size - two to three inches in diameter - and have grown quickly and without interruption; old turnips tend to be tough and woody; successive plantings at ten-day intervals provide later harvests of quality roots.

Risk fades when: A woody root does not turn tender again. Pull turnips at two to three inches across; the shoulders sit above the soil, so size is easy to judge without digging. Water about an inch a week - a big storage root on a small root system means drought toughens it fast. Grow them in the cool halves of the season rather than through summer heat, and sow small successive plantings about ten days apart so roots reach size in sequence instead of waiting in the ground. An overlarge turnip is still edible - cook it rather than eating it raw.