Greenhouse Abortions: The Death of Tomato Blossoms

“Hello, It is too unfortunate. Not one seedling set blossoms this year. I planted in peat pots and   they have been in the green house since.  Not a single blossom has set .I am not new to tomatoes nor to your advice.  Get your facts straight. ~Mary”


Hi Mary,

Thank you for the email regarding your tomatoes.  I’m sorry to hear that you have had problems with them.  Sounds like they are suffering from too much nitrogen or a condition called blossom drop.

Too much nitrogen prevents the plants from setting blossoms.  Nitrogen promotes green growth (i.e. foliage).  An overdose of nitrogen will trick the plant into assuming that the environment it is in is favorable for unending growth.  While a plant normally has an end goal of producing seed, too much nitrogen prevents this from occurring.  To avoid having this occur in the future, use a fertilizer that is low in nitrogen, and high in phosphorus and potassium (which help to promote blossoming and fruit set).

If there are very tiny blossom initials that develop, but are aborted (fall off) before they actually blossom, then your plants are suffering from blossom drop.  Blossom drop is a common tomato growing problem that can be extremely frustrating to the home gardener. Otherwise healthy looking tomato plants set flower blossoms, only to have them dry up and fall off the plant before a fruit is formed.

Blossom drop can be attributed to several causes, most often related to either temperature and / or stress.

–Temperature Too High or Too Low

–Lack of Pollination

–Humidity Too High or Low Humidity.

–Lack of water

–Stress from insect damage or disease

Grow varieties suited for greenhouse production.  The high summer temperatures in a greenhouse will cause any non-greenhouse variety to become shocked and drop its blossoms or not form them to begin with.  The most frequent cause of tomato blossom drop is temperature.

–High daytime temperatures (above 85 F / 29 C)

–High Nighttime Temperatures (Below 70 / 21 C)

–Low Nighttime Temperatures (Below 55 / 13 C)

Tomatoes grow best if daytime temperatures range between 70 F / 21 C and 85 F / 29 C. While tomato plants can tolerate more extreme temperatures for short periods, several days or nights with temps outside the ideal range will cause the plant to abort fruit set and focus on survival. Temperatures over 104 F / 40 C for only four hours can cause the flowers that are beginning to develop on the plant to abort and prevent more buds from developing for about 1-2 weeks.

Tomatoes need some help to pollinate in a greenhouse. Either insects, wind or hand shaking of the flowers is necessary to carry the pollen from the anthers to the stigma.

The ideal humidity range is between 40 – 70%. If humidity is either too high or too low, it interferes with the release of pollen and with pollens ability to stick to the stigma. So pollination will not occur.  If humidity is too low, hose the foliage during the day. This will both cool the plant and raise the humidity. This is not recommended in areas with high humidity or when fungus diseases are present.

Water deeply, once a week, during dry weather. Tomatoes have very deep roots, sometimes going down into the soil up to 5 feet. Shallow watering will stress and weaken the plants and prevent them from setting fruit.

Keep your tomato plants healthy. Use good cultural practices and treat for disease as soon as symptoms appear. Sometimes the problem is just too much of a good thing. When a tomato plant has too many blossoms, the resulting fruits are all competing for the limited food supplied by the plant. Only the strong will survive. The plant will automatically abort some flowers. Once the initial crop is harvested, the problem should subside.

Nothing will guarantee fruit set. Things like temperature and humidity are out of the gardener’s control. Sometimes you just have to be patient and wait for conditions to correct themselves. If the weather seems fine and other gardeners in your area are not having fruit set problems, you should consider the cultural causes of tomato blossom drop. Choosing a suitable variety and keeping your plants healthy will give you an edge.




© Mertie Mae Botanics LLC and Horticulture Talk!, 2011. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.


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