Why do my flowers drop without setting fruit?
A healthy plant covered in flowers that sets nothing is usually a temperature or pollination story rather than a disease. Pollen is temperature-sensitive at a narrower range than the plant itself, so a plant can look perfect and still be sterile for a fortnight.
The one observation that decides it
Line the drop up against the weather two to three weeks earlier, not against today. Flowers that yellowed at the base of the stalk and fell complete, in waves matching a heatwave or a cold snap, are blossom drop. A tall flowering stem shooting from the centre of a leaf crop instead is bolting, and it ends that plant's useful life. Blackened blossom centres after a clear cold night are frost damage, and blossoms that wilted brown and stayed attached on a fruit tree are blossom blight.
Start from the plant in front of you
7 things it could be
Ordered by how much they can cost you — if the first entry fits what you can see, rule it out before considering the milder ones.
Blossoms and shoots suddenly wilt, blacken and bend into a shepherd's crook as if scorched by fire; sunken cankers ooze amber bacterial droplets in warm weather.
Conditions: 21–30°C · humidity ≥70% · wet leaves / rainFirst move: Remove affected material nowSeen on: Apple trees, Pear trees, Quince
Blossoms wilt and turn brown (blossom blight); fruit develops expanding brown firm rot covered with tan spore tufts; mummified fruit clings to the tree over winter.
Conditions: 18–28°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysLeaves and shoot tips blacken, go limp and hang down, then dry to brown paper within a few days. Blossom turns brown at the centre and sets no fruit. Split bark and dieback on woody plants may not appear until weeks later.
Conditions: ≤2°CFirst move: Fix the cause, not the leafSeen on: Walnut trees, Lavender
Upward curling and cupping of leaves, yellowing of margins, severe stunting with bushy shortened growth, and heavy flower drop with little or no fruit.
Conditions: Spread by handling, insects or soil — not weather-triggeredFirst move: Remove affected material nowFlowers yellow at the base of the stalk and drop off complete, leaving a bare truss with no fruit set. It happens in waves that match a heatwave or a cold snap a week or so earlier, while the plant itself looks perfectly healthy.
Conditions: ≥32°C · dry air ≤40%First move: Watch it before you actA tall flowering stem shoots up from the centre of the plant. Lettuce and spinach turn bitter and milky, onions and beetroot form a hard woody core, brassicas produce a thin stalk instead of a head, and coriander and rocket run to seed within days.
Conditions: ≥25°C · dry air ≤50%First move: Fix the cause, not the leafSeen on: Lettuce, Onions, Beetroot, Radishes, Spinach, Broccoli and 3 more
Brown, corky patches inside beetroot, swede and celeriac roots. Cauliflower curds go brown and the stem is hollow with a brown lining. Growing points die, young leaves are brittle and distorted, and fruit sets poorly.
Conditions: dry air ≤45%First move: Fix the cause, not the leafSeen on: Beetroot, Cauliflower, Celeriac