University of Vermont Extension
Department of Plant and Soil Science
WHY PLANTS FAIL TO FLOWER OR
Dr. Leonard Perry, Extension
University of Vermont
your flowers failed to flower, or didn’t last as long as you’d like
season. Maybe your neighbor's yard is
ablaze with color every summer, yet for some reason those shrubs you
few years ago still haven't flowered. Perhaps
your shrubs, trees or grapes that should have had fruits didn’t.
If you’re wondering why plants failed to
flower or fruit, you’re not alone as this is one of the most common
fail to flower for various reasons. Herbaceous plants may have been
foliage not flowers, such as coleus and many of the new coralbells.
Some perennials may have been “forced” or
manipulated into bloom out of season by the grower so they’ll be in
during the May sales season. The next
year this same plant might bloom later in summer during its normal
of the more common reasons for bloom failure with woody plants is
“juvenility”. Trees, in particular, must reach a certain age before
if the plant is old enough, the growing conditions may be too poor
flowering. Plants that require full sun, for instance, may grow but
flower in the shade. And, if a plant is
too old, as often is the case with perennials, they may flower
poorly if at all. Peonies are an exception to most perennials,
not flowering if they are planted with their base of the plant from
arise (the “crown”) more than a couple inches deep or under mulch.
winter temperatures may kill the flower buds. This often happens to
and some spring bulbs. Unfortunately, nothing can be done to prevent
of injury except to buy more hardy cultivars (cultivated varieties).
woody plants generally have separate flower and leaf buds, the
latter being more hardy,
cold in winter will often kill the flower buds yet the plants leaf
fine. Or, the flower buds may only open
on the bottom, as is common with forsythia—those buds being
protected by snow
cover. When choosing fruit trees, if you
live in a cold pocket with late spring frosts, plant late-blooming
that are not fully hardy will be most susceptible to cold injury.
This is why
it is important to not fertilize woody plants the last half of the
season, so plants will harden properly for winter.
pruning may cause failure to flower. Some plants bloom only on last
wood, particularly spring bloomers like lilacs and rhododendrons.
right after bloom, if needed at all. Cutting
the plants back severely or too late removes all the flowering wood
coming year. This happens with pruning climbing roses improperly.
This might explain, too, why some shrubs (as
some of the new hydrangeas) that die back to the ground each winter
need to keep last year’s wood and buds alive.
plants fruit on last year’s wood, such as summer raspberries, and
once. So cut the old fruiting canes back
in late fall, which allows time for nutrients to recycle back to the
roots. These raspberry canes won’t fruit
again if left on the plant. And, cutting
canes back that are only one-year old will remove fruiting wood for
with nitrogen can sometimes cause plants to grow only leaves and
plants, often herbaceous or woody perennials, will be quite large
flowers. Yet many of the new annual
flowers are bred to require heavy fertility.
With too little fertilizer for such annuals, they may stop blooming
mid summer. Some annuals just bloom for
a shorter period and not late into the season.
You can see online which annual flowers have lasted best through the
summer at our Burlington, Vermont All-America Selections display
plant may fail to fruit because of the same reasons as for failure
If there are no flowers, there can be no fruits. Then again, a plant
but fail to have fruits. One of the most
common explanations is lack of proper pollination. Some plants
themselves. They require a plant of the same species but of a
cultivar for cross-pollination. Plants
should be somewhat close (often 50 feet or less) so bees will go
plants. And the different cultivars
should, obviously, overlap in bloom time. Some fruit trees get
as to what pollinates what, information provided in catalogs and
of pollination can occur if cold, rainy weather occurs when a plant
is in full
bloom. Such weather will keep bees from working, thus reducing or
pollination and fruit-set. Or, bees may be more tempted by adjacent
weeds such as dandelions, so not pollinate pear trees for instance
if plums are
in bloom nearby. A frost while a plant
is in flower also will kill the flowers and prevent fruit-set. Some
woody plants or vines, such as grapes,
have another set of buds that will come out if the first is
damaged. So, if the first buds are killed with a late
frost, the plant may flower and fruit but just less heavily.
plants are "dioecious" meaning all the flowers on a plant are either
male or female. Both a male and a female plant must be present, and
cross-pollination must occur for the female to produce fruit.
dioecious plants are holly, bittersweet, and yew.
cultivars of fruit trees, in particular, are “alternate bearing” or
bearing”. This simply means they may
bear heavily one year, then take a break the next to recoup their
few, if any, fruit. Bosc pears, and
Golden Delicious or Fuji apples, often have alternate bearing.
all these reasons for not flowering or fruiting are based on either
or its culture, another may just be wildlife.
Serviceberries, elderberries, currants, blueberries and the like may
be picked by the birds and seem to disappear
overnight. Deer may have pruned back your perennials, as they do
with my garden
phlox, so they never bloom if feeding keeps up through the season.