Why
Flowering Shrubs Fail to Bloom
It is sometimes difficult
to determine just why a particular plant will fail to set flower buds or will
set them and then not develop flowers. One or more of the following conditions
or situations may be the reason a plant will not bloom.
- Nitrogen-Carbohydrate
Ratio Problem: Too much nitrogen fertilizer is used and vegetative growth
is encouraged at the expense of the development of flower buds. If this is
the case, a slight root-pruning in early summer may encourage flower-bud formation.
This is done by inserting a spade slightly within the outside limit of the
branches at various places in a circle around the plant, so approximately
one-third of the roots will be severed.
- In some cases the plants
do not have a sufficient amount of phosphorus available. If this is suspected,
a shallow trench can be dug around the plant, and a cupful of superphosphate
or two cups of bonemeal or a cup of 0-20-20 for every three running feet of
the ditch can be mixed with the excavated soil. This soil with the phosphate
is then returned to the ditch.
- Too shady a location.
Many ornamentals must be grown in a sunny location. Even rhododendrons may
produce more bloom if given more sunlight.
- Competition with adjacent
shrub and tree roots.
- The plants were planted
too deep so the roots are lacking sufficient soil and air.
- Occasionally, some people
prune them in midsummer, fall or early spring and cut off all the flower buds.
- Too many suckers at the
base of the plant will limit the number of blooms. Most of the over-vigorous
suckers should be pruned to the ground.
For more information contact:
Tom Kowalsick, Extension Educator - Horticulture,
CCE - Suffolk County
Horticulture
Leaflets Online
4/03
