Pull a few plants. A radish that's all tops has big, healthy leaves and a root no thicker than the stem, or a thin taproot with a slight swelling. Check how close the plants are. If leaves overlap and roots touch, crowding is the likely cause. Look for a flower stalk rising from the center. That's , and once a radish starts to bolt, the root usually turns woody and won't fill out. Count the days, too: most spring radishes size up in 25 to 30 days, so a planting at 18 days may be fine.
Crowding is the most common cause. Radish seed is cheap and fast, so it tends to go in thick, and plants that touch compete for water and light and put their energy into leaves. Heat comes next. Radishes grow best when temperatures stay below about 80°F. A sowing that runs into early summer, or a sudden warm spell, often pushes plants toward leaves and flowers instead of roots. Too much nitrogen gives lush tops with little root. Fresh manure or a high-nitrogen fertilizer worked in before sowing is the usual source.
A few other things can add to it. Dry spells in the first weeks of growth can trigger early flowering. Radishes in partial shade tend to stay small. Winter radishes like daikon are meant for late-summer sowing, and spring-sown plants often bolt before the root forms. If you planted a winter type in spring, the variety may be the whole story.
A crowded planting that hasn't bolted can still recover. Thin right away so plants stand 1 to 2 inches apart and keep the soil evenly moist. You may still get usable roots within a week or two. Plants that have sent up flower stalks won't form good roots, so pull them and eat the greens. Radish greens are edible, with a mild mustard flavor. Then resow in cooler weather rather than waiting on a planting that's already bolted.
Next time, sow 2 to 4 weeks before your last spring frost, half an inch deep and about an inch apart. Thin to 1 to 2 inches as soon as seedlings are up. Sow small batches every 10 days through the cool weeks instead of one big sowing. Give radishes full sun, skip fresh manure and high-nitrogen fertilizer in their bed, and water evenly. When summer heat ends the spring window, wait for cooler late-summer weather and sow again for fall.
- Flea BeetlePinhole shothole damage across leaves with tiny jumping beetles that scatter when touched.
- Cabbage MaggotBrassica transplants wilting and dying as white maggots tunnel through roots at or below the soil line.
- Fruit CrackingTomatoes crack at the stem end or shoulder, cabbage heads split, and carrots split lengthwise — usually after heavy rain follows dry weather.
- Early BlightDark spots with concentric rings on lower leaves that yellow and drop, working up the plant.
- Nitrogen DeficiencyUniform yellowing starting on the oldest, lowest leaves while new growth stays green — nitrogen is being pulled from old tissue to feed new growth.
- Can you give a plant too much nitrogen, and what does it look like?Yes — excess nitrogen produces very dark green, lush leafy growth at the expense of flowers and fruit, and in high concentrations can burn roots and cause wilting.
- Why did my broccoli skip making a head and go straight to flowers?Broccoli bolts when it experiences heat or stress during head formation — once it starts flowering, the head is unsalvageable, but timing adjustments can prevent it next season.
- How do I know if my soil is compacted, and what can I do about it?Compacted soil pools water after rain, resists a probe or screwdriver pushed by hand, and produces stunted plants with shallow root systems — the fix depends on severity and whether you're willing to leave soil undisturbed over time.