Here are some of the most common reasons and cures for poor bloom:
Spring bloomers flower from buds that form in the previous summer. Shearing or
pruning the plant at the wrong time of year strips the plant of its potential flowers.
Remember it's always safe to prune a flowering plant immediately after bloom.
Fruiting in some plants inhibits flower bud formation for the next year. Snip
out the flower clusters when they no longer look nice.
Years of neglect-accumulated drought stress, soil compaction and low nutrient levels
can keep a plant from performing non-essential functions such as flowering. Address
these problems in the right amounts at the right time of year.
Older landscapes often show a gradual loss of sunlight as the trees fill in and block
the sun from reaching the understory. The solution here is to gradually change the
landscape over the years to put in more shade-tolerant plants, or to remove or prune or
limb up the trees.
If a plant has been in the ground less than 3 seasons, it may still be recovering from
transplant shock. It needs time to get its roots established before it can support
flowering. For larger trees, it takes about 1 year per inch of trunk diameter for
the tree to be considered established.
There are critical times of the year for each species as they form flower buds.
For spring-blooming plants, this is in the summer. If there is a drought and the
plant gets no supplemental water, it may not be able to set buds. Pay attention to
watering for summer blooming plants in the late spring and summer.
This article is adapted from Jo Mercer, Extension Educator, Horticulture, University of Delaware.