Soil temperature and blossom drop?

venturabananas · July 18, 2021

Can high soil temperatures lead to blossom drop?

I grow most or all of my tomatoes in pots, usually 20 gallon pots with 2-3 plants per pot. The pots are black plastic and the soil in them really heats up on sunny days.

I've always read that high temperatures can lead to blossom drop, failure to set fruit. I had always assumed the problem was related to air temperature, not soil temperature. I'm fortunate to live in a place (coastal California) where a typical summer day seldom even reaches 80F and nighttime lows are in the low 60's. From what I've read, this temperature range should be ideal for fruit set. Yet during mid-summer, for a couple of months, my plants make lots of blooms and drop them all. They set fruit earlier in the season, in late spring, and later, in fall.

This year I decided to start measuring the soil temperature in the pots. By early afternoon, the soil temperature is 95-100F on a typical summer day. First thing in the morning, it is in the high 60s.

My best bet is the high soil temperatures during the day, or the high fluctuation in temperature, in the root zone is stressing the plants and causing blossom drop. The plants are otherwise healthy. They don't wilt and they grow well.

In support of the soil temperature hypothesis, this blossom drop seems to only happen on plants in pots fully exposed to the sun all day. One plant in a pot that is shaded in the afternoon doesn't drop blossoms, nor does another one planted in the ground. But that could be coincidental.

Do any of you have any definitive information or experience on whether high or fluctuating soil temperatures can cause blossom drop?

July 18, 2021	#1
venturabananas Tomatovillian™ Join Date: Feb 2012 Location: Ventura, CA Posts: 142	Soil temperature and blossom drop? Can high soil temperatures lead to blossom drop? I grow most or all of my tomatoes in pots, usually 20 gallon pots with 2-3 plants per pot. The pots are black plastic and the soil in them really heats up on sunny days. I've always read that high temperatures can lead to blossom drop, failure to set fruit. I had always assumed the problem was related to air temperature, not soil temperature. I'm fortunate to live in a place (coastal California) where a typical summer day seldom even reaches 80F and nighttime lows are in the low 60's. From what I've read, this temperature range should be ideal for fruit set. Yet during mid-summer, for a couple of months, my plants make lots of blooms and drop them all. They set fruit earlier in the season, in late spring, and later, in fall. This year I decided to start measuring the soil temperature in the pots. By early afternoon, the soil temperature is 95-100F on a typical summer day. First thing in the morning, it is in the high 60s. My best bet is the high soil temperatures during the day, or the high fluctuation in temperature, in the root zone is stressing the plants and causing blossom drop. The plants are otherwise healthy. They don't wilt and they grow well. In support of the soil temperature hypothesis, this blossom drop seems to only happen on plants in pots fully exposed to the sun all day. One plant in a pot that is shaded in the afternoon doesn't drop blossoms, nor does another one planted in the ground. But that could be coincidental. Do any of you have any definitive information or experience on whether high or fluctuating soil temperatures can cause blossom drop?