Why is my orchid dropping flowers (bud blast)?

What bud blast is, and what it is not

Bud blast is the specific term for buds that yellow, shrivel, and drop off before they ever open. It is different from an open flower fading at the end of its natural life, and it is almost never a sign of pest or disease. A Phalaenopsis decides whether to finish opening a bud based on the stability of its surroundings. When something changes sharply, the plant treats those developing buds as an expense it can no longer afford and aborts them to conserve energy. The plant itself is usually fine: firm leaves, healthy green roots, and it will spike and bloom again once conditions settle.

The most important clue is timing. Bud blast almost always follows a recent event: a trip home from the shop, a repotting, a move to a new room, or the day the heating switched on for winter. If buds dropped within a week or two of one of those events, you have your answer.

The triggers, roughly in order

Several environmental factors can tip a budding orchid over the edge. They often combine, which is why bud blast can feel mysterious. The University-backed habit of working through environmental conditions one at a time applies well here; Iowa State University Extension's guide to diagnosing houseplant problems from improper environmental conditions lays out how light, temperature, humidity, and watering interact to stress a plant.

• General shock from a move. The shift in light, temperature, and humidity between the shop and your home is the classic cause of buds dropping days after purchase.
• Temperature swings. A spot near a radiator, oven, cold single-glazed window, or an outside door exposes buds to hot or cold spikes; they tend to shrivel fastest on the side facing the source.
• Low humidity. Phalaenopsis prefer 50 to 70 percent humidity. Dry winter air from central heating, often down at 20 to 30 percent, dries buds out before they can open.
• Watering stress. Letting the bark go bone dry, or keeping it constantly soggy, stresses the roots enough to drop buds. Check whether the bark is parched or waterlogged.
• Draughts and ethylene gas. Air-conditioning vents, heating ducts, and even a bowl of ripening fruit nearby (apples and bananas release ethylene, which signals flowers to drop) can trigger blast.
• Natural end of bloom. Open flowers fading one by one from the base of the spray after weeks of display is the bloom simply finishing, not blast.

A worked example

You bring home a Phalaenopsis covered in open flowers and a dozen fat buds, and set it on a kitchen windowsill above the radiator. Within ten days the unopened buds yellow and fall while the open flowers and the leaves stay fine. Two triggers stack up here: the shock of the move from the shop, plus the temperature swing from a hot radiator under cold glass. Neither is a disease. Move the plant to a steady, draught-free spot away from the radiator, hold humidity around 50 to 70 percent, and stop relocating it. The open flowers will run their course and the next spike of buds should hold.

How to stop the drop

1. Stop moving it. Choose one stable spot with bright indirect light and leave the orchid there while it buds and blooms.
2. Steady the temperature. Keep it between 18 and 27 degrees Celsius (64 to 81 F) and away from radiators, ovens, cold glass, and exterior doors.
3. Raise the humidity. Aim for 50 to 70 percent by grouping plants, using a humidity tray, or running a small humidifier in dry rooms.
4. Block draughts. Move it clear of air-conditioning vents, heating ducts, and frequently opened doors.
5. Water consistently. Water when the roots turn silvery, roughly every 7 to 10 days, so the bark is neither parched nor soggy.
6. Remove nearby fruit. Keep ripening fruit out of the room, as the ethylene it releases can trigger bud drop.
7. Keep the green spike. Leave a green spike in place to rebloom; only cut it to the base once it has fully browned.