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The three main causes of your magnolia tree not flowering are related to its environment, your care and maintenance of it, and infestations.
Have you purchased a suitable variety for your environment?
The first thing to check is whether your variety of magnolia is suitable for your local environment. Some varieties do better in warmer climates while others can tolerate cooler places such as Magnolia Stellata and Susan. Read the label that came with the tree to see if your general climate is one that the tree prefers. If your tree is in too colder a climate, it won’t die but it may not flower; the flower buds are very sensitive to their surroundings. If you purchase a magnolia from a local nursery or garden centre then usually it will be suitable for your local environment.
Could it be that an early frost got to those buds
Then take a look at where you’ve put the tree. Magnolia trees and shrubs need full sun but they can manage in partial shade. They should be in a sheltered place, out of the way of cold winds. And also away from any exposed areas that are susceptible to heavy frost on cold nights. Maybe your magnolia is the early blooming type and tried to flower while there was still frost. If the buds look blackened, that’s an indication of frost damage and that’s a good reason why the magnolia is not flowering.
Maybe the soil is not suitable
Then check the quality of the soil. The best soil is well-drained and with a slightly acidic pH of 5.5 to 6.5 on the pH scale. A neutral soil is fine too. You may need to adjust the soil’s pH by adding minerals or organic material.
Simply too young to flower
If your tree is in its first few years of life, maybe you’re being too impatient. Young trees take a while to become established and settle in before they start flowering.
Care and maintenance
Are you looking after your magnolia shrub or tree well? In its first few years, the tree needs regular watering and nutrients from a dedicated fertiliser or organic mulch. It may not bloom in this period but it still needs to create energy to grow strong.
Hard pruning can remove the flowering shoots early on and lead to few flowers
And you may have been excessive in pruning your magnolia tree. It’s not necessary to prune the tree except to remove diseased or dead tree limbs or to help the air circulate through the branches. Over-pruning may have removed many of the buds that usually turn into flowers.
This dreaded word usually applies to the hordes of bugs that may use your magnolia tree as their private buffet. Their presence is definitely a cause of your magnolia not flowering but it would have to be severe.
First of all, take a close-up at the leaves and buds (if any) of your tree. You’re looking for any sign of actual bugs or the debris they leave behind.
Thrips are a hazard that attack flowers, leaves and stems. These moth-like insects with flimsy wings suck the juices out of whatever’s growing as part of the tree. Look for a discoloured/silver-coloured stippling on the leaves and stems. If you find it, then you’ve got thrips.
These bugs are very invasive as the weakened tree is not open to many diseases that the thrips spread as they go from plant to plant. Use insecticidal soap to thoroughly wash the infected parts of the tree.
As for other bad bugs such as scale insects on the stems and buds, check all over for honeydew. This is a white sticky substance left by a variety of insects as they chew away at your magnolia tree. if you find some, assume that the insects are still around, even though you may not be able to see them, and spray with soap. Or use an insecticide if the infestation seems bad.