Tomatoes Forming but not ripening

steve333_gwAugust 26, 2013

Having an unusual problem in my greenhouse (small, personal use only) with my tomatoes this year, my old reliable plant variety (a Cobra derivative) is not ripening fruit. Lots of green tomatoes on the plant, with plenty of healthy foliage and new flowers, but the fruit never ripens. Typically this variety will ripen fruit and continue to produce new fruit throughout the season. This year there are new flowers and fruit setting, but the older fruits just stay green.

There is one difference this year from past seasons: I grafted a couple of tomatoes onto commercial rootstock. I did this because I was seeing some disease problems with toms in the GH and thought that grafting onto resistant roots might help. And it may have, we are 60% of the way through the season and no signs of disease yet which is way better than last and previous years.

However both grafted tomatoes (this Cobra and a cherry) are growing way more leaves than usual and the cherry is producing somewhat fewer flowers and fruit than usual. I don't believe that I have increased the level of N over past years, but have not had the soil analyzed this year either. And we have had more rainy weather this summer than typical (although that only effects the amount of sun and temps in the GH).

I am just curious if anyone knows if one of the effects of grafting tomatoes onto commercial rootstock is a delay in the ripening of fruit? Any other things which might be causing this?


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It could be too much nitrogen in your growing medium. Raise the potassium levels and fruit production will be shifted into a higher gear. Nitrogen grows beautiful foliage, but too much can hinder fruit development.


    Bookmark   August 26, 2013 at 1:53PM
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albert_135(Sunset 2 or 3)

I had lots of tomatoes ripening daily when the temperatures hit 100F each afternoon. Now that temperatures only get to near 90F green tomatoes just hang there for two weeks. I asked on this forum and the one response was that 90F should be an ideal temperature. This time the answer seems to be potassium. Hummm?

    Bookmark   August 26, 2013 at 2:03PM
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zzackey(8b GA)

MMMM! From what I read on the Florida Gardening site, they stop fruiting at 90 degrees. Sorry I don't know why this is happening to you. I grew 3 types of heirloom tomatoes this year and I really wasn't impressed with how they grew or how little they produced or how they tasted had a well composted hugel. The basils and flowers grew like crazy.

    Bookmark   August 26, 2013 at 7:27PM
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seysonn(8a WA/HZ 1)

I think, the high temps can hinder new fruit setting, but with the existing fruits, as long as plant is fed and watered, it should not make a difference. Maybe to the contrary, higher temps should hasten fruit ripening.

    Bookmark   August 27, 2013 at 4:44AM
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I've had the same problem in the field - I think cooler temps and less sun (even if not a lot of rain) will delay ripening.

    Bookmark   August 27, 2013 at 7:17AM
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seysonn(8a WA/HZ 1)

Another point is that, tomatoes can stay in green/growth stage for a LONG time(40 day ?). with large fruits it can even take longer. So, if there have bee new sets(late comers) , it will take them a while to grow and ripen.

And yet another point: In zone 5, CO, if the wether has been cooling off, it will slow down both growth and ripening.

The other point, already mentioned, is that if you fertilized with nitrogen rich stuff, the plant will concentrate on foiliage growth.

    Bookmark   August 28, 2013 at 10:54PM
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i don't grow in a greenhouse,i live in northern alberta and my tomatoes are red and the plants are over 7 fertilizer,just rain

    Bookmark   August 30, 2013 at 6:27PM
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