Wednesday, March 18, 2009

Tomato Flowers

Sinfonian's Square Foot Garden had an article today that talked about tomato flowers and I started to comment, but it just got too long, so I'm putting it here for everyone. As many of you know I'm doing a little tomato experiment growing F2 seed that I saved, so I've been doing a little research in tomato breeding and seed saving and have come across a lot of info.

There are two kinds of tomato flowers. Most modern tomatoes have the first kind. These have short styles. The anthers (the male part of the flower that produces pollen) form a cone around the style and the stigma (the female part that accepts the pollen at the end of the style) is totally enclosed. Bees can't get to the stigma to pollinate it, so they are totally self pollinating. Bees actually do help with pollination here. Studies have shown that the frequency of the bees buzzing is perfect to loosen the pollen and make it fall on the stigma. Wind also helps and shaking the flowers can help too. If you grow in a greenhouse, shaking the plants is mandatory for fruit set.

The second kind of tomato flower has long styles. The stigma sticks out past the cone of the anthers. These don't always self pollinate. They can be pollinated by bees in the usual way. They can cross with other tomatoes. Sometimes they self pollinate like the other tomatoes (and they don't need bees for this, if the flower is pointing down the pollen can still fall on the stigma). However the seed collected from these tomatoes may not be true to type.

So how can you tell if your tomato has long or short styles? Most modern varieties have short styles, but as I found out earlier you can't be sure. My Sungolds from which I saved F2 seed might have crossed with my others since they have long styles. The wild tomatoes all have long styles. According to Suzanne Ashworth's book, Seed to Seed, all potato leaved tomatoes have long styles as do beefsteaks when they have double blossoms. If you want to save seed from your tomatoes it is always a good idea just to check the flowers first. Just look at the cone formed by the anthers. Does the style stick out past it or not? If it does, you have to isolate your plant if you want to save seed. I'll probably do this by making little remay bags for the flowers, since mine will all be planted in one 20'x20' garden. Oh and when you check those styles, make sure it is from newly opened blossoms. Once they are pollinated, the anther tube will start to open and you will see the style then.

Though tomatoes pollinate themselves just fine, that doesn't mean all your tomatoes will automatically be pollinated and if they aren't pollinated no tomato will be formed unless it is parthenocarpic (if you want to read about that go to Sinfonian's SFG and click the link to the article he references). What causes a tomato not to pollinate? Temperature is the major culprit. Low temperatures can cause the flowers to be malformed (55°F 13°C) and pollen is usually not viable under 50°F 10°C. I don't see high temperature problems here in the Boston area, but the same thing happens when the temperature goes over 90°F 32°C.

Please note that those temperatures are an estimate. There is a lot of genetics at play about what temperatures the flowers are viable. Some have been bred for temperature extremes and can produce where others can't. Strange things can happen to the plant at temperature extremes too. If your tomatoes don't self pollinate at high temperatures, the flowers can sometimes elongate their styles in an attempt to try to cross with viable pollen. This is a very cool survival mechanism since the resulting seed will always have some genes for high temperature survival. Though if you want true to type seed, don't save seed when temperatures get that high.


  1. Wow, I had no idea there was so much to learn about tomato flowers. Thanks for the enlightenment!

  2. Great post Daphne, I've not tried to save seed from tomatoes yet because I was never sure if even the flowers with short styles couldn't get cross pollinated by a busy bee. Sounds like not, so perhaps I'll give it a try this year.

    Temperature really does affect pollination. I think it takes about 24 hours for pollination to occur in tomatoes and the temps must be right for that entire time. Around here the night time temps don't reliably stay above 50F until late June or so. I don't get much fruit set until July or August. The one tomato I've grown that sets well when night time temps are low is Paul Robeson, which happens to be delicious.

  3. I always thought that all tomatoes had short styles and would only self-pollinate, except maybe wild varieties. I'm glad you mentioned some exceptions to this "rule".

  4. These tomatoes are interesting characters. I read about their pollination awhile back and it was rather interesting. I figure if I save seed and it is a cross it may produce an even better tomato so no need to worry.

  5. Boy, I hope my tomatoes are going to be okay! I had to put them in the greenhouse because I was going out of town this week and they were getting too big in the house- the lower temps should slow down growth a bit, and I hope that's all!

    Great info, Daphne- I always learn so much from you :)

  6. Sheila your welcome

    Michelle interesting, you are in zone 9 and still have trouble with cool summer temperatures. We get some ocean cooling, but not all the time. Our June lows average about 55F. Tomatoes do set during June since the average temperature does not tell the whole story. We get warm spells on and off. The tomatoes set when the wind is blowing in from the south west and rarely when the wind blows from the north east.

    Cassandra most do have short styles. I think saving seed is fairly safe for most varieties. And when you grow the seed out the next year you will be able to tell anyway if you got crosses. As long as you aren't selling or trading them to others it is a fun enough experiment to just save them and grow them out. You might get something fun.

    Dan, I feel the same way. As long as I get something out of it. If I get really awful tomatoes or no fruit I might not be happy. I might get something wonderful.

    Tessa, as long as that greenhouse doesn't get too hot or too cold :> It is so hard to travel when you little babies are growing.

  7. What a great post...who knew tomato flowers could be so interesting? Kim

  8. Wow, this is a great article. I can't wait to hear more about your progress.

  9. Great post! Boy, you went above and beyond what I posted. Amazing. I still don't get it. I'm more of a trial and error kind of guy. Science was always interesting but beyond me. hehe.

    Thanks for sharing!