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Post by daylilydude on Apr 10, 2019 4:14:02 GMT -5
My seedlings have nice, green leaves. . . . but with purplish undersides... what causes this and how do I fix it?
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Post by coppice on Apr 10, 2019 6:30:26 GMT -5
Patience grasshopper, this too shall pass. When plants are slightly chilled they struggle a little to take up phosphorus. Making the purple leaf you note happen. As days warm it goes away.
*Edited to make correction.
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Post by brownrexx on Apr 10, 2019 7:39:34 GMT -5
When plants are slightly chilled they struggle a little to take up potasium. Absolutely but actually it is phosphorus not potassium. No intervention needed. It will correct itself as the weather warms. You could have the plants sitting in a pile of phosphorus and they would still be purple because they can not absorb it until they are warm enough. This is the same thing that happens with calcium. Many people want to add calcium to prevent BER but most soils have adequate calcium already, it's just that the plants can't absorb it due to conditions. By soil test, my soil has an excess amount of calcium and I still occasionally get some BER especially if I would grow a paste type tomato. Edited to add that I thought that it was already warm in TX. If you are experiencing purple leaves and the weather is not cool, then maybe your soil needs a little magnesium which you can get from epsom salts. Magnesium works to help the plant absorb phosphorus.
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Post by paulf on Apr 10, 2019 8:48:26 GMT -5
Yup, what they said.
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Post by Laura_in_FL on Apr 10, 2019 9:19:10 GMT -5
You're absolutely right about purple leaf undersides due to phosphorus deficiency caused by too-cool conditions.
But with BER it can also be that the soil is too acid for the plants to take up calcium no matter how much calcium is in the soil. Even when the weather warms, BER continues. Correct the pH and the BER resolves. So if you see BER you want to check your soil's pH. Or better yet, if BER has been a problem for you in the past, check your soil's pH in the fall and correct it then if needed. Lime can take a few months to react with the soil.
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Post by brownrexx on Apr 10, 2019 9:37:18 GMT -5
I just checked on my tomato seedlings. I have been putting them outside on the deck for the last 3 days when the daytime highs have been in the 70's and I wanted them to have some "real" sunlight.
However the mornings have been a bit cool.
I just brought the babies indoors because it is getting too windy and they are not strong enough for that yet. I noticed that most of them have some purple on the undersides of the leaves. Some have more than others so maybe it is related to the variety since they are all planted in the same soiless medium.
Actually I think that it's kind of a pretty color.
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Post by paulf on Apr 10, 2019 10:44:47 GMT -5
For BER, like Laura says a pH from 6 to 8 will allow abundant calcium to be taken up by tomatoes. Anything higher or lower is in the risky range. For me lime would skyrocket my pH into the 9 area. Likewise, sulphur applied on my garden to lower the pH takes a while so I add it in the fall. Besides pH, temperature swings early in the growing season and irregular watering, either from the sky or from a hose, are the other factors affecting BER. Some varieties are more sensitive than others as well.
For me, the lack of phosphorus uptake causing purple leaves only happens to my seedlings in the cool basement. After planting outside it goes away quickly. My thought is does your seed starting medium have a little bit of fertilizer in it? Or do you add a little plant food in your watering schedule every week or so? Since I have used soillesss mix with a slow release fertilizer I have not noticed purple leaves.
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