Ask a Question forum: Trouble with some of my petunia seedlings

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Name: Bob Randall
Southeastern Massachusetts (Zone 6b)
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PuzzlerBob
Feb 5, 2018 11:03 AM CST
I've started my wave petunia from pelitized seeds a bit early to have enough time to propagate them though cuttings.

I planted the seeds in Jiffy Natural & Organic Seed Starting Mix on January 20, 2018, with a heat mat and controller set to 78 F. They germinated very well, popping up in only 4 days and most by the 6th day. Germination percentage was very high. I only put 1 seed per cell, with a few cells not getting any. That's because the packet of seeds were typically 11 per, and I kept each variety within 2 groups of 6 cells.

These pictures are taken today, 16 days after planting the seeds. The last watering was 2 days ago. A few cells show they are starting to dry on the top but I'm sure they are wet enough underneath. Probably won't water again until tomorrow or the day after.
Thumb of 2018-02-05/PuzzlerBob/1b6eb7

Some seem to be doing quite well...
Thumb of 2018-02-05/PuzzlerBob/046069

But the Shock Wave Coconut is in a bit of trouble showing some yellowing of the leaves, and are not as big as the others. It's the 4 in the center of this picture:
Thumb of 2018-02-05/PuzzlerBob/1e6e0a

All have been treated the same. I water them well, then wait until they are dry which is about 3-5 days. The peat moss in the Jiffy Mix can be quite stubborn to rewet once it drys so I bottom flood the trays until it shows it's wet on the top, then I remove the bottom water. I don't top water for fear that I'll have no idea if the water properly penetrated the peat.

I didn't start fertilizing until there were a few sets of true leaves. For fertilizer I used Grow More Mendocino Water Soluble Fertilizer Bloom 9-21-12. I read somewhere to start seedlings with something like a 1-2-1 ratio, i.e. P twice as high as N and K but that it's not critical. I am trying to avoid over fertilizing, but also feel it's best to fertilize with each watering but in trace amounts. So I used 1/8 teaspoon per gallon of water. Watering twice a week this is the equivalent of 1/2 teaspoon of fertilizer per gallon every 2 weeks.

For light I'm using a MEIZHI LED Grow Light 600W and have surrounded the 4 sides with reflective mylar to even out the light. It can breath through the bottom and out the top so there's adequate air flow. This is working fairly well. The PAR values are from 275 to 350 uMol/m^2/S depending on where you take the reading. The lights are on 16 hours a day resulting in a total Daily Light Integral (DLI) of 16-20 mols/day which is what it should be based on https://www.extension.purdue.e...

So my main concern is the yellow leaves on the Shock Wave Coconut, but also there doesn't seem to be as uniform of a growth throughout the flats on the whole.

I'm not an expert gardener so I'm looking for opinions from those of you that can tell by my data and looking at the photos how I should tweak things.

Thanks,
Bob
Name: Sue
Ontario, Canada (Zone 4a)
Daylilies Birds Enjoys or suffers cold winters Native Plants and Wildflowers Butterflies Annuals
Region: Canadian Keeps Horses Dog Lover Plant Identifier Garden Sages
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sooby
Feb 5, 2018 12:49 PM CST
Do you have any idea what the pH of the Jiffy mix is? Or maybe you irrigagtion water? Some petunias have a tendency to iron chlorosis and this can be brought on by a high pH, and also high phosphorous can interfere with micronutrient availability to the plant. I think your fertilizer probably has iron and manganese in it but it may not be enough to counteract a high pH or high P. Can you switch to a fertilizer that is not high in P?
Name: Bob Randall
Southeastern Massachusetts (Zone 6b)
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PuzzlerBob
Feb 5, 2018 4:41 PM CST
I just purchased a meter from my local home improvement store but it's hard to read. Maybe 7.5

I've ordered a digital meter for easier reading. Assuming I need to lower the pH what's the best way to do this? I can't mix it into the soil at this point since it already has seedlings. Perhap I could mix something with the water. Is that the right way to do it?
Name: Sue
Ontario, Canada (Zone 4a)
Daylilies Birds Enjoys or suffers cold winters Native Plants and Wildflowers Butterflies Annuals
Region: Canadian Keeps Horses Dog Lover Plant Identifier Garden Sages
Image
sooby
Feb 6, 2018 6:01 AM CST
Yes, you can mix something in the water but I would wait until your digital meter arrives to see if it really is 7.5, which seems high for a commercial mix. If you can get chelated iron locally at a garden store you could also try that. I would test it on one or two of the seedlings first to see if it does anything before using it on all of them.

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