Figuring out why a plant doesn’t bloom, or why one thrives and another doesn’t, is often a hopeless task. Sure, SOMETHING isn’t making the plant happy…. but you’ll have a dickens of a time deciding what it is specifically.

The first thing to consider is the light level around the plant. Light is food for a plant: if it doesn’t get enough light, it won’t have the energy to grow or to reproduce (bloom). Make sure you know the appropriate light conditions your plant needs before you plant it. If your plant is already in place, does it get the same amount of light it got years ago? More or less light could be the cause of its present problems. Consider moving the plant or pruning trees around it.

The second environmental condition to consider is the soil around your plant’s roots. The vast majority of landscape plants prefer soil that is loose (not hard clay). Water should be able to drain through the soil around the plant and away from it within a day after a rain. If the soil is hard, if it stays too wet or if it stays too dry, roots can’t prosper. Maybe you dug a hole originally that was a good size for the plant… but it has grown so much that the roots have “hit the sides” of the hole. If that is the case, consider digging up the soil in a large area around the present root system of your plant.

How far out should the soil be loosened? One tool developed by Dr. Kim Coder at the University of Georgia states that the distance (in feet) that roots extend from the trunk of a tree is equal to 2.5 multiplied times the thickness of the trunk (in inches). For example, a dogwood tree trunk that is 4 inches in diameter (measured four feet from the ground) signifies that its critical roots extend 10 feet away.(2.5 x 4 = 10). More secondary feeder roots extend out from there.

If your plant is a shrub, a rough estimate is that healthy roots extend .75 of its height and width added together. For example, a holly that is 6 feet tall and 6 feet wide needs a good root environment extending 9 feet from the trunk (.75 x 12 = 9).

Before blaming your plant’s poor performance on bad fertilizer or something else, make sure it gets the light and root resources it needs.

That brings us to fertilizer. It is true that blooms are influenced by plant nutrients… but fertilizer is less important than the light and soil conditions discussed above. If your soil is greatly deficient in phosphorus, blooming and fruiting are lowered. If the plant can’t get enough nitrogen, it will grow poorly and the leaves will be light green.

If your problem is poor blooming, you can try using a “high phosphorus” fertilizer such as GreenLight Super Bloom (12-55-6). This may help or it may not. The effects of additional phosphorus will be slow – you might have to wait for a year to see any change.

A final explanation for poor blooming is the plant’s genetics. If you transplant a dogwood or magnolia from the woods, you have no idea who its parents were. It could be the progeny of two poorly blooming plants and could have inherited their paltry propensity. In this case there is nothing you can do but enjoy the foliage!

The bottom line is that a healthy plant blooms when it is happy. You can help it be happy by providing the right light level, soil conditions and nutrients.

For more information, visit these links from other state Extension offices:

Clemson University

University of Rhode Island

University of Vermont

Purdue University