What Causes Blossom Drop on Tomatoes?
Temperature stress. When nighttime temperatures drop below 55F or daytime highs exceed 90F, tomato flowers often fall off without setting fruit. In Santa Cruz, cool foggy nights are the more common trigger, though inland gardens can hit both extremes.
Tomato flowers need a specific temperature window to pollinate successfully: roughly 55F to 85F. Outside that range, pollen becomes non-viable and the plant drops its blossoms as a survival strategy. UC IPM notes that inconsistent temperatures, high humidity, and low humidity can all interfere with pollination. In Santa Cruz County, the pattern usually looks like this: a warm week gets flowers forming, then a fog bank rolls in, nighttime temps dip into the low 50s, and the blossoms drop.
The good news is that blossom drop is temporary. Once temperatures stabilize within the viable range, new flowers will set fruit normally. You have not done anything wrong, and there is no spray or treatment that fixes it. The plant is simply responding to conditions you cannot control.
What you can control: choosing varieties that tolerate cooler conditions (Stupice, Glacier, and most cherry types handle temperature swings better than large-fruited varieties). You can also improve air circulation by spacing plants adequately and pruning lower branches. In coastal gardens, planting near heat-absorbing surfaces like stone walls or concrete paths can raise overnight temperatures by a few degrees, which is sometimes enough to keep flowers viable.
This week: Check your tomato plants for small yellow flowers and note how many are dropping versus holding. If most are falling, check overnight lows for the past week. If they have been below 55F, patience is the only real fix.
Our Troubleshooting Guide covers blossom drop alongside other common tomato problems. For a deeper look at variety selection and microclimate strategies, see the Tomato Growing MasterKit.
