Why your tomato flowers are falling off

The first July I grew tomatoes, I went out one morning and found a little scatter of yellow flowers on the soil under my plants. My heart sank. I was sure I'd done something fatal: overwatered, underwatered, killed them with kindness somehow.

So I did what any reasonable person does. I panicked, googled for an hour, and very nearly ripped out a perfectly healthy plant. Don't be me. The flowers were dropping because of the one thing I had zero control over: the heat.

Why tomato flowers drop in the heat

Tomato flowers drop when daytime temperatures climb above about 85 to 90°F or nighttime temperatures stay above about 70 to 72°F. At those temperatures the pollen goes sterile and tacky, so the flower can't pollinate itself and the plant simply lets it go.

Here's the part nobody tells you: this is the plant being smart, not sick. A tomato flower has to pollinate itself to set fruit. When it's too hot, the pollen clumps up and won't do its job, so the plant cuts its losses and drops the bloom rather than waste energy on fruit that was never going to form. It's triage, not failure.

So if your plant looks green and strong but the flowers keep falling, look at your thermometer before you blame yourself. Nine times out of ten in summer, that's the whole story.

The other reasons (and how to rule them out)

Heat is the usual culprit in summer, but a few other things cause blossom drop too: inconsistent watering, too much nitrogen, too few pollinators, or not enough sun. Run down this list before you worry.

1. Water stress. Tomatoes hate a feast-then-famine watering schedule. Let them bone-dry out and then drown them, and they'll drop flowers from the stress. Water deeply and consistently so the soil stays evenly moist, not soggy, not parched.

2. Too much nitrogen. If you've been feeding a high-nitrogen fertilizer, you'll get a gorgeous, leafy, jungle of a plant with hardly any flowers (and the ones it makes may drop). Ease off the nitrogen and let the plant put its energy into fruit instead of foliage.

3. Lonely flowers. Tomatoes self-pollinate, but they need a little movement (wind or a visiting bee) to shake the pollen loose. In a still, sheltered spot with few pollinators around, the flowers can drop unfertilized. A gentle daily shake of the plant, or a soft brush (even a clean electric toothbrush held to the stem) does the bees' job for them.

4. Not enough sun. Tomatoes want at least 6 hours of direct sun. Much less than that and the plant won't have the energy to hold and ripen fruit, so blooms drop. If yours is in a shady corner, that's worth fixing for next time.

What to do while you wait out the heat

You can't change the weather, but you can keep your plant comfortable so it's ready to set fruit the moment things cool down. A few simple moves carry it through.

Drape a length of 30 to 40 percent shade cloth over the plants during the hottest afternoon hours to take the edge off the worst sun. Water deeply and on a steady schedule so the roots never swing between drought and flood. Hold off on high-nitrogen feed. And give the plant a gentle shake each morning to help any flowers that do form pollinate while the pollen is still good in the cooler air.

Then, the most important step of all: don't panic. Once daytime temperatures fall back into the 70 to 85°F range and nights cool below about 70°F, fruit set resumes on its own. Your plant didn't fail. It just hit pause. Every gardener with a thermometer and a tomato has watched this exact thing happen, and watched the fruit come right back when the heat broke.

Common questions about tomato flowers falling off

At what temperature do tomato flowers drop?

Tomato flowers usually drop when daytime temperatures climb above about 85 to 90°F or nighttime temperatures stay above about 70 to 72°F. At those temperatures the pollen turns sterile and sticky, so the flower cannot set fruit and the plant drops it.

Will my tomato plant make fruit again after the heat passes?

Yes. Blossom drop from heat is temporary. Once daytime temperatures settle back into the 70 to 85°F range and nights cool below about 70°F, your plant sets fruit normally again. Keep it watered and healthy through the heat and it will pick right back up.

Want the full beginner's path from bare patch to thriving garden in one place? It's all in my Backyard Garden book for beginners.

Happy growing!
Priscilla