Petunias are heavy feeders I believe. Mine too turn yellow, so now I just use a dilute fertilizer solution in a mister bottle every time I water. Seems to help. I know that people say to bottom water, but I find that it just makes everything too wet and soggy, especially young seedlings. I just use a mister with a fine spray, and be sure never to water at night (so the water doesn't sit on the leaves). I have never had a problem with disease, knock on wood, from watering this way. Everyone has their own way of doing things. I would just try and start misting them a couple times a day rather than bottom watering them, its worth a shot?

I will try that. Also, could it be my lights. These young plants are under cool white bulbs only for 14-15 hours. Should I have 1 cool and 1 warm? I did notice, though, that the 6 packs on the south facing window (gettin real sunlight) are also displaying yellow on some of the petunias, but not the tobacco. All plants are in Premier Horticulture PGX seed starting mix. I'm stumped!

Sounds like your petunias might be suffering from chlorosis. Chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. A few things that can cause chlorosis are iron deficiency, wrong soil pH, or poor drainage.

Petunias have a difficult time taking up iron compared with other plants, but more acidic soil helps them intake the nutrient. According to the University of Massachusetts, petunias grow best with a soil pH between 5.5 and 5.8. With a higher soil pH, petunias begin to suffer from an iron deficiency.

You might try alternating your fertilizing (keeping with reduced strengths of course) with a fertilizer rich in iron. One possibility would be Miracle-Gro for acid loving plants.

Art33,
I purchasesd the Miracle-Gro for acid loving plants. could you reccommend a reduced doseage for the petunia seedlings. I'm not sure what to use and don't want to do more damage. Also, should they receive the fertilizer dose at every watering or every other watering? Thanks, John

Hi John,

Well, I don't know if petunias can really be classified as "acid loving" or not. However, I do know that they are very sensitive to a high pH, which will cause the leaves to turn yellow.

Regarding using reduced fertilizer dosages for our seedlings, we often see suggestions that recommend one fourth strength. The problem is that any recommended percentage may be weak for one fertilizer and still very strong for another. And, of course, one fourth strength probably isn't going to be right for all plants.

If you're using Miracle-Gro Miracid (30-10-10) you might try one fourth strength, at least at first to green up those leaves. I'd use it with every watering but not more than once a week. Later on you could go back to using your regular fertilizer or maybe use the Miracid once a month just to make sure the petunias are not too low on iron.

Keep in mind that I'm no expert and this is simply what I would probably try. Good luck with the petunias, hope they turn out beautiful!

Art

John,

One other thing, I forgot to mention... try to avoid getting the fertilizer on the leaves. The leaves of seedlings can be easily burned.

Art

Art, Thanks for the help. 1/4 teaspoon sounds good.
John

how do you get iron for plants, can you buy it in plant stores, how do you test the soil for yellow leaves on petunias?

Hi,
Yellow leaves usually means they need acid, also, petunias love heat. A cool envionment will cause rot and wilting. Acid will give them a dark green strong leaf.