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.........

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

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

.....Alan.

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.