An experiment to try

24 years ago

Hi,

Don't know if any of you have been following the discussions on the Garden Experiments Forum re using cornmeal to combat fungus disease problems. If not, suggest you check them out. Among the many plants that I have been tossing cornmeal under is gardenias. So far the gardenias are not experiencing the heavy yellow leaf problem they usually do after they bloom. And, for the past three years I have been trying to coax three young, variegated gardenias into growing and their leaves have repeatly browned and fallen off....up until I used cornmeal under them beginning two months ago. It is the first time since I planted them I would call them healthy looking plants.

So, I am asking you to start throwing about a pound of regular, muffin-type cornmeal under a few of your large gardenias once a month and see if you notice a diminuation in the amount of yellow leaves. Quickly wet the cornmeal down with the hose after spreading. I am curious to see if any of you note a difference. Thanks.........

Featured Answer

nandina
Original Author

23 years ago

To Dawtawgal - Cornmeal should be applied only during the warmer months as it needs heat to do it's thing. Also, it contains 10% nitrogen and it sounds as though your plant has been pushed into overgrowth with excess nitrogen. We still do not have all the answers re cornmeal and blackspot. I suspect your black spot leaves will drop off and the rose will recover and grow well during the rest of the summer. But, I would not fertilize it for awhile. Try mixing up a cornmeal tea (1/4 cup cornmeal to 1 cup water, allow to sit for 24 hours, strain through a coffee filter and spray on roses) and see what results you get. Keep in touch with me on this.

To WannaBeGardener - If all your gardenia leaves are a uniform yellow-green indicating a lack of iron this is not the type of yellow leaf to which I was refering. I am talking about that period of time after the bloom when the bush has a large number of bright yellow leaves which fall off the bush eventually. It appears that several cornmeal treatments about a month apart beginning just as the buds form seems to greatly reduce this yellow leaf problem. I am hopeful that others will try cornmeal and let me know if they see an improvement in their gardenia bushes.

As to the general chlorosis (lack of iron) problem which plagues gardenias it is important to understand that neither plants nor humans can absorb iron without the presence of magnesium. Our soils lack magnesium. A scattering of Epsom salts under iron starved plants and shubs along with an application of Ironite every third month usually solves the problem. You are using rusty nails as an iron source which is fine if they contain iron. I collect used iron horseshoes from farriers and bury those under my mulch. They work well, too.

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Comments (12)

Blooming_annie
24 years ago
Thanks Nandina. I'll give it a try. My gardenias are newly planted as of this year but sounds like an interesting experiment. Maybe I'll put it under one and not the other and what happens.
nandina
Original Author
23 years ago
Knock....Knock! Did any of you try this cornmeal experiment on your gardenias? I hope so because it would be interesting to hear your results.
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mrskjun
23 years ago
I don't have gardenias, but did try it on some newly planted rose bushes that went straight to blackspot and yellowing leaves. It worked really fast. The leaves with BS and yellowing dropped off and new green healthy leaves are coming out. Only thing I wonder about, the cornmeal that remained on top of the soil grew some fuzzy mold, and wonder if that could be a problem in itself.
nandina
Original Author
23 years ago
mrskjun,
Thanks for your report. You are one of several in Florida (only) who has reported 'fuzzy mold' on the cornmeal applications. Keep an eye on the situation and post if you suspect problems. Yes, it appears that cornmeal may be the answer to the rose grower's nightmares; black spot and mildew.
Shari_in_SC
23 years ago
Greetings from South Carolina!

From reports of those who claim to know about such pathogens, it seems that the cornmeal encourages a harmless fungus which grows and fights off Black Spot and Powdery Mildew spores. It sure seems worth a try.

Happy Gardening!
Shari

Here is a link that might be useful: Cornmeal on Roses
Datawgal
23 years ago
I tried it on a florabunda rose planted in a large container. It was hard to keep an even soil moisture level in containers this past summer and this weakened the plant. It was almost defoliated from black spot. The corn meal really seemed to help, there have been only a few infected leaves (maybe one a week) since the meal was applied. I'm sold!
athagan
23 years ago
Wonder if this would work on summer squash?

Always seems to be powdery mildew that does in my squash every summer. Think I'll give the cornmeal a try.

.....Alan.
Datawgal
23 years ago
OK Nandina, I need help - big time. The potted rose that I had been having such good luck with is now suffering with black spot. I kept applying the corn meal and it just got so healthy and lush through the winter. Then came the monsoon rains and it was just too full of leaves and I guess there wasn't enough air circulation. Now, even with the corn meal applied regularly I am pulling off spotty leaves every day. I have pruned a number of branches (all with buds), anything else I should be doing?
Thanks. Ali
Micimacko
23 years ago
Not much luck with cornmeal, I am afraid, though I applied to every rose bush in my yard.
Try a second application and if that does not help, I return to regular fungicides.
So much I hoped this would work!
WannaBGardener
23 years ago
Thank you for the tip, Nan. Wish I had read this sooner. I have a large gardenia, that no matter what I do to it, the leaves are still yellow. Done fed it everything on the market, and even as a last resort, took my friends advise and put rusted nails in the soil around the plant. This morning I am breaking out the cornmeal. Wish me luck. Its loaded with buds, but I hate those yellow leaves.
imasweetp
22 years ago
I have a trailing gardenia that I got as a gift..I washed it with soapy water when it developed white cottony spots on it and now they are back...is this powdery mildew and how do I permanently get rid of it???