I am growing some Doub... #118195 - Ask Extension


I am growing some Doub... #118195

Asked March 20, 2013, 5:38 PM EDT

I am growing some Double Cascade Petunias indoors under grow lights. I am having some issues with some of the leaves turning yellow, see attached picture. I used Miracle Grow Organic potting soil and water only about once every 5-6 days(soil is usually dry at this time). I irrigate from the bottom but they are in tray with drainage hole so they aren't sitting in water for long periods of time.(I lost several last year because I used solid trays and they sat in water for long periods, root rot). I have feed them with Miracle Grow regular plant food. There is a light infestation of gnats but didn't know if this is a cause. Any advise would be greatly appreciated. Thank You, Keith Lake

Hamilton County Ohio

Expert Response

Yellow foliage on petunias may be caused by nitrogen or iron deficiency within the plant. Symptoms of nitrogen deficiency include general yellowing of older leaves. Symptoms of iron deficiency include general yellowing of leaves with veins remaining green, starting with youngest leaves. Both can be corrected with the proper supplemental fertilizers. However you need to be careful because young, tender seedlings can be easily damaged by too much fertilizer.  Fertility is not a critical factor for most plants during germination and root emergence because most seeds have enough stored nutrients to carry out germination. Also the soil you used may have had a starter charge of fertilizer which supplies nutrients as the root grow. The most important factors for germination are temperature of the soil and a proper balance between moisture level and aeration. When the first seed leaves and the first set of true leaves develop you can start with a diluted fertilizer program and the rate of application can be gradually increased as the seedlings grow larger and approach transplanting.The gnats could be fungus gnats, symptoms may appear as sudden wilting, loss of vigor, poor growth, yellowing and foliage loss.  More information on identification and control measures of fungus gnats can be found at http://ohioline.osu.edu/hyg-fact/2000/2114.html .
Julie Crook Replied March 25, 2013, 2:45 PM EDT

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