When you plant a flowering ornamental tree, one of its main appeals usually is that it’s flowering. Of course, the blooming period only lasts a few weeks at best, but the burst of color and/or fragrance in your yard is a highlight of the gardening year and something to look forward to, especially after a long winter. But what if your Japanese cherry, dogwood, crabapple, or other flowering tree isn’t blooming?
The failure to bloom can have several reasons. The tree needs to be suitable for your local climate, a location too warm can be just as detrimental as too cold. It requires a certain type of soil, the right amount of light, sufficient fertilizer with the right nutrient content, and correct pruning at the right time.
Each tree species is different so when determining the cause of why your tree isn’t blooming, it’s important to familiarize yourself with its specific needs.
Why Trees Fail to Bloom
Before you get into the problem-solving why your tree isn’t blooming, make sure you properly identify the tree. Magnolia species, for example, vary greatly in their bloom time and light requirements. For trees that you have bought from a nursery and planted yourself, identification is usually easy. But if you moved to a new home and the tree is already there, determining what you have might require some research.
Here’s a list of common reasons why a flowering ornamental tree isn’t blooming.
The Tree Wasn't Pollinated
Check that your tree isn't a sexed tree. If you have a female tree, you need a male tree to pollinate it. You can get one and plant it nearby, or graft male stems onto the female tree. If you have a male tree, your tree won't bloom on its own; you'll have to graft a female tree onto it. Sometimes trees are both male and female and can technically pollinate themselves but have have mechanisms in place to prevent excessive inbreeding, so you may just need to plant a duplicate tree to broaden the gene pool.
Flower Bud Damage
If a tree does not flower but seems otherwise healthy, it could be that the climate is simply too cold for the species and variety. The flower buds are less hardy than the leaf buds, which is why a tree might survive a cold winter with temperatures below -20 degrees Fahrenheit and leaf out in the spring, but its flower buds are killed by the cold.
Since it’s not feasible to protect an entire tree against the cold, there is not much you can do other than planting varieties that fit your hardiness zone.
Even if a tree is perfectly suited to your local climate, a severe late spring frost can damage the flower buds and result in no bloom that year.
Insufficient moisture can affect the flowering of a tree although you might not see the effects of it immediately. If there is a severe, extended drought when trees that bloom on old wood develop their buds for the next season, and they aren’t given extra water, they might not bloom the next spring. To prevent this, make sure to water the tree during a drought.
Pruning at the Wrong Time
When a tree has been pruned at the wrong time or too heavily, it might not bloom because the flower buds have been accidentally removed in the process; instead, you will get a lot of vegetative growth, which is encouraged by pruning.
Trees can bloom on old or new wood, and must be pruned accordingly. The correct timing is also crucial here. For example, Japanese flowering cherry needs to be pruned right after flowering to encourage the growth of new buds in the same season, which will become next year’s flowers. Make sure to follow the specific instructions for pruning each tree species.
There could be issues with the soil. Is the soil compacted? Has there been any construction nearby that could cause root damage? If the soil is compacted, you can aerate it.
Established trees that grow in healthy soil generally get an adequate amount of nutrients and don’t need fertilizer. But if a tree isn’t flowering, and you can rule out all the other reasons, adding a fertilizer high in phosphorus (indicated by the high number for “K” on the fertilizer label) might help it bloom the next year. You can also apply mulch around the base of the tree all the way out the to the drip line. The mulch works as an organic slow-release fertilizer.
To determine if and how much fertilizer should be added, a proper soil test is indispensable. Adding fertilizer based on purely guessing can harm the tree; in fact, erroneously adding a fertilizer high in nitrogen will only lead to excessive vegetative growth, instead of flower buds, and structurally weaken the tree.
Soil test kits are available from your local Extension Office. You can also buy do-it-yourself soil test kits at home improvement centers.
The proper light conditions are crucial for flowering. Most trees require at least six to eight hours of direct sunlight to bloom. However, the more sunlight the better does not apply to all. Flowering dogwoods, for example, do best in partial shade. Knowing the tree’s needs is key to understanding whether lack of light might be the problem.
A tree needs to be mature in order to flower and your tree might not have reached that stage yet. The number of years until a tree reaches maturity varies considerably from species to species. There is no correlation between the growth rate of a tree and its flowering. For example, a tulip poplar grows fast but it can take up to 15 years for it to flower. For lilacs, on the other hand, you can expect to see bloom within three to five years after planting.
Not Enough Sunlight
To foster more positive flowering conditions, prune neighboring plants to give your tree more access to light, or even remove them if they do not add visual value to the landscape.
Not every tree will flower with the same abundance every year; there might be a heavy bloom one year and only a sparse bloom the next year. This phenomenon, also known as biennial bearing, occurs mainly with fruit trees. Of the flowering ornamental trees, this phenomenon occurs especially in crabapples.