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tomDear Tom –

We have part of our tomato crop in a high tunnel this year.  They have been very productive but some of the fruit are small and oddly shaped.  We are also seeing some blossom drop with no fruit forming.  The outside tomatoes are fine except for blight. Any suggestions?

-Bill in Waynesville

tomato 1

Dear Bill –

Your hoop house may be raising the crop temperature enough to be causing pollination problems.   Seventy to 82 degrees is ideal for tomato pollination.  Their flowers have both male and female parts in the familiar cone that we see in tomato blossoms.   Some movement is needed to transfer the pollen.  In field tomatoes wind causes blossom movement and pollen transfer.  Depending on how your hoop house is vented, limited pollen may be moving to the pistil because of reduced wind.  Persistent high humidity or wet conditions can make the pollen grains sticky so they fail to transfer within the flower.  Night temperatures above 70 F interfere with the growth of the pollen tube to the future fruit.  Day temperatures in the high 90s can interfere with pollen production.  If pollination does not occur in a few days the blossom will drop and no fruit is formed.

tomato2

With partial pollination few seeds are formed in the developing tomato.  Each seed is encased in a gel which provides part of the tomato flavor but gel also helps fill out the fruit adding size and weight.  With few seeds in a developing tomato several physical changes can occur – small fruit, angular fruit (triangles, squares, or just flat-sided), points on the blossom end, or hollow fruit with space between the seeds and the outside wall.  With lots of seeds and lots of gel around those seeds, fruit fill out normally without odd shapes or empty space inside the fruit.

Several options exist for managing heat in a hoop house.  Greenhouse suppliers sell shade cloth which is expensive but normally reduces inside temperature.  They also have spray-on materials, some of which are easily removed after frost.   Reducing light also reduces production but that may be a better choice than unsalable fruit.  Venting the full length of the house is normal in summer months but also removing the ends may help.  Mid-day misting helps with some crops but probably is not a good idea with tomatoes because prime time for pollen transfer is 11:00 to 4:00.

Some highly automated greenhouse ranges now have roofs that open on sunny days.  If you are feeling inventive, a roll-off roof might be an option.  A longer range strategy could involve supporting public officials that see value in managing climate change.

-Tom

Tom Elmore is co-owner and operator of Thatchmore Farm in Leicester NC.  He has grown certified organic fruits and vegetables for 25 years and serves on the Boards of the NC Greenhouse Vegetable Growers Association and the Organic Growers School.

 

Sources:  

Photos c/o Delaware Cooperative Extension https://agdev.anr.udel.edu/weeklycropupdate/?p=4489

Dr. Randy Gardner – NCSU Mt. Horticultural Crops Research and Extension Center

http://msucares.com/pubs/publications/p1828.pdf

http://www.uaf.edu/files/ces/publications-db/catalog/anr/HGA-00435.pdf

https://agdev.anr.udel.edu/weeklycropupdate/?p=4489

Tom Elmore

Tom Elmore

Tom Elmore is co-owner and operator of Thatchmore Farm in Leicester NC. He has grown certified organic fruits and vegetables for 25 years and serves on the Boards of the NC Greenhouse Vegetable Growers Association and the Organic Growers School.