May
2005
By
B. Rosie Lerner
Extension Consumer Horticulturist
Purdue University
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Why Plants Fail to Bloom
Flowering plants that don't bloom as promised can be a big disappointment
in your garden. Reasons for lack of blooming are as diverse as the palette
of plants from which to choose, but a little detective work can usually
pinpoint the trouble. The most common factors associated with blooming,
or lack thereof, include light, plant age, nutrition, extreme temperatures
and improper pruning.
Many woody plants must reach a certain age before they are mature enough
to produce flowers. Fruit trees, such as apples and pears, can require
as many as five or six years to become fruitful. Gingko trees can take
up to 15 years to bloom. Add a stressful environment to a juvenile plant,
and flowering may be delayed even further.
Plants that are old enough to flower, or have done so in the past, may
quit doing so for a variety of reasons. Flowering may be sparse or completely
absent when a plant is under stress, so be sure the plant is positioned
in an appropriate location for that particular species. For example, some
plants flower best in full sun; others may prefer the cooler conditions
found in the shade. Some plants, such as peonies, will flower sparsely
or not at all when grown in shade. Similarly, shade-loving plants, such
as begonias, will not bloom well in full sun. In gardens where other trees
and shrubs are nearby, light conditions can change drastically over time
as landscape plants cast more shade, or removal of a large plant suddenly
leaves formerly shaded plants exposed.
Some plants, such as chrysanthemums and poinsettias, flower in response
to short day lengths, or more accurately, long nights. If the plants don't
receive the appropriate break from light, their season of bloom will be
delayed indefinitely.
Overfeeding plants with nitrogen can encourage them to produce lush foliage
at the expense of blossoms. A lack of nutrients, particularly nitrogen,
phosphorus and potassium, also may delay flowering. Stick with a balanced,
low-analysis fertilizer, such as 12-12-12 or 6-10-4, to apply adequate
nutrition without overdoing.
Some gardeners unknowingly remove flower potential from their plants by
pruning at the wrong time of year. Landscape plants that bloom in early
spring set their flower buds in autumn on last year's growth. If you prune
these plants in late winter, you'll also be removing many or all of the
flower buds. The rule of thumb is to prune spring-flowering shrubs and
vines after blooms have faded.
Mother Nature can deal a blow to buds with extreme low winter temperatures
or late frosts in spring after growth has begun. Though this past winter
was relatively mild, we did have some late spring freezes. And some plants
may be winter hardy, but their flower buds are routinely killed, even
by normal spring weather. A common example is the big-leaf hydrangea,
successfully grown in southern Indiana and beyond, but in northern Indiana
often just provides great foliage but rarely, if ever, blooms.
So if you have landscape plants that are not performing up to par, do
your homework to find the appropriate requirements, and plan to replace
the "duds" with plants that are better adapted to your growing
conditions.
5-19-05
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