One of the hardest questions to answer is why isn't my plant blooming. The plant is usually an apple tree or a crapemyrtle tree but occasionally camellias or houseplants won't flower. I know several things which can cause plants not to flower but often I suspect the problem is something beyond what I know.
Shade causes a lack of blooms. Crapemyrtles may need four or five hours of sunshine. Apples would prefer full sun but will usually have a few flowers with only one or two hours.
Sometimes crapemyrtles can get shaded by sooty mold. Sooty mold is a black fungus that grows on sap on the leaves. The sap comes from aphids. Sooty mold doesn't hurt the tree but blocks the sun. In following years, a tree with heavy sooty mold will have fewer flowers than one that hasn't had an aphid infestation.
Some gardeners think poor nutrition may cause a plant not to flower. They usually blame low phosphorus levels. I have said the same thing because I heard other people say it. It would be a nice theory but in my experience it hasn't panned out. I have never seen a soil test confirm phosphorus deficiency on a plant that wasn't blooming. I have seen plants that started blooming a few years after phosphorus was applied but I suspect they would have bloomed anyway. Poor nutrition may be a contributing factor to poor plant health but I have quit looking at that as a primary factor.
On some plants it may take several years for the plant to grow up and start producing fruit. Standard apple trees may take 8 to 10 years to start blooming. If a dwarf apple sends out roots above the graft, it will act like a standard plant. So gardeners expecting a small tree that flowers in 3 or 4 years will get a big tree that flowers in 8 to 10 years.
Anything that makes the plant more vigorous will delay flowering. Heavy pruning during the winter and too much nitrogen fertilize will make the plant more vigorous.
Apples and other plants put on a balancing act between getting bigger and reproducing. When young they try to get as big as possible to avoid getting shaded out. As long as they have plenty of energy they keep getting bigger. Once they have gotten some size, they then try to reproduce. If you vigorously prune an apple tree every winter, it has more energy and will grow bigger instead of blooming. Heavy nitrogen every year has the same effect. Backing off the pruning and fertilizing will allow the plant to become mature.
Heavy pruning can also take off blooms that formed the previous year. Most shrubs like azaleas and forsythia will have a few blooms but I have seen homeowners totally prune the blooms off other shrubs. Most of the common flowering shrubs form their blooms the previous year. A few exceptions include buddleia, crapemyrtles, and sasanqua camellias.
This past year, I had one okra plant that never bloomed. I never figured out if it had a genetic or virus problem. If it was genetic, it won't be a problem with the new crop. If it was a virus, I should have yanked it out but I was so curious to see what would happen I never did.
In part 2 I talk about why plants flower but don't set fruit.
Article was written by David Goforth Agriculture Extension agent North Carolina Cooperative Extension Cabarrus County Center. Visit my homepage http://cabarrus.ces.ncsu.edu/ or http://cabarrus.ces.ncsu.edu/index.php?page=lawngarden or my blog http://gardeninggurugoforth.blogspot.com/
Contact me at David_Goforth@ncsu.edu. Reviewed 2007.