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Elisabeth C. Miller Library

Keyword: Failure to flower

Encouraging Chilean fire tree to bloom

I have a Chilean Fire tree (Embothrium) that I planted about four years ago. It has grown rapidly to about seven feet tall. It has not yet bloomed. At what size or age does this tree bloom? Does it require some encouragement, like root pruning, to get it to bloom?
I have not fertilized it because I have read in at least two sources that these plants should not be fertilized.

 

There are many reasons a plant may fail to flower, immaturity being one of them. You are correct to avoid over-fertilization, as that is often a cause of lack of flowers. Another cause is unusually cold weather.

I found an article by Roy Lancaster on Embothrium coccineum in Gardens Illustrated, May 2005. He mentions that if the tree is planted in a somewhat shady site, it will not flower as prolifically. Acid soil which is moist but well-drained, and a sunny but sheltered spot are ideal.

There is a discussion of the problem of Embothrium’s failure to flower on the NPR Talking Plants blog (no longer online) in 2007 (formerly hosted by Portland gardener Ketzel Levine). It appears that this is not an uncommon problem. Here is an excerpt, from a gardener responding to Levine’s complaint about the lack of flowers:

“Many have found Embothrium to be a slow bloomer. It is a polymorphous plant in many ways: some are evergreen, some deciduous, some are trees, some are shrubs. Some bloom in a 1-gallon container, others need to put on some size first.

“The danger of phosphorus toxicity rules out some of the usual bloom-stimulation therapies using fertilizer. Provided that it’s getting enough sun exposure, I’d say just sit tight and give it a few more years. If you’ve been watering it on a consistent basis all summer, hold back and let it dry out for a few weeks between good soakings.

“If you get really desperate and are contemplating its removal, you might first take a propane torch and try burning the leaves and twigs off when autumn comes (don’t scorch the bark on major limbs). I know that sounds a bit absurd, but some plants respond to environmental adversity by blooming, and the fire trick has been known to work on some other proteaceous flora. From the plant’s point of view, why expend the energy of going into a reproductive cycle when everything’s fine and there’s no threat to survival? Give ’em something to worry about.”

If you feel daring or desperate, I suppose you could try the blowtorch approach, or you could make sure to provide the ideal conditions, and wait patiently. Levine, like you, thought of root-pruning her Embothrium to induce flowering. You could try to contact her and ask if she tried it or the fire method, and if either worked.

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Non-blooming Wisteria

We have a Chinese wisteria which we’ve had for 20 years. We’ve
trained it on a trellis to the side of our covered porch and then
on a rope across the front so there is a nice green, leafy fringe
along the porch front. However, this plant has never bloomed.

We have consulted with our local horticultural experts and they have suggested various treatments. The lawn care
people do not fertilize near the roots of the wisteria so it
doesn’t get too much phosphorus, we have done root pruning, we have
even hit the trunk with a board to shock it, have applied super
phosphate but no blooms. We get some pretty cold
winters, but I’ve never even seen flower buds anywhere on the
plant. I know wisterias are sometimes late in blooming, but this
is a long time to wait! The roots of the plant face east and get
lots of sun. The part across the porch is shaded in the afternoon
because we have two pine trees in the front yard. We prune off the
tendrils that form during the summer to keep the plant in check,
but what else can we do to get blooms? I know it would be a
spectacular display if it ever bloomed and have almost given up
trying. I’m thinking of hanging artificial blooms just to get the
effect!

 

 

I found quite a bit of discussion in online gardening forums about
flowerless wisterias, so you are not alone. You may find this information
from Cass Turnbull of Plant Amnesty helpful:

“THE MOST COMMON COMMENT I get at classes and at the PlantAmnesty
educational booth is, “My wisteria won’t bloom.” It is natural for these
vines to take between three and seven years to start blooming. I have
read that frequent, proper pruning may help them to begin blooming
sooner, or at least more. On the other hand, some people have old vines
that have never bloomed. I am told that these are seed grown plants or
“mules.” I have often heard root pruning recommended to force an older
vine to bloom. Basically, this means that you use your shovel to cut the
roots in a circle (or dotted circle) a foot or two from the vine. I have
also heard people recommend fertilizer formulated to encourage blooms,
(not heavy on nitrogen). However, I have been faced with such a vine and
had no luck with either technique. In that case, as with all
non-performers, removal is the best option, and no one will blame you for
it.”

Here are gardener Ketzel Levine’s comments, from her NPR.org site:

“Depending on how old your wisteria is, do know that young plants can take
up to eight or ten years before they flower, especially if started from
seed. Other reasons wisteria fail to bloom: lack of adequate sunlight
(needs at least six hours of full sunlight); too much nitrogen fertilizer
(causes more vegetative growth); pruned heavily in winter or spring (also
encourages vigorous vegetative growth); severe winter injury/cold-blasted
flower buds (though that is clearly not a problem this year) or a bum
plant. It happens.”

You could either try the method described above, of cutting a circle with
a shovel, or you could replace the vine, or you could follow through on
your artificial flower idea! (I’ve heard that Bellevue Botanical Gardens
hangs Wisteria-shaped lights from their arbor for their holiday light
show.)

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Staghorn sumac flowers and fruit

I planted three staghorn sumacs several years ago. They have done well, and have nice fall color, but I was hoping to see the flowers and fruit. This summer, for the first time, there are flowers on one shrub. What prompted the change? Will the flowering plant have fruit?

 

Anecdotally, there are reports of Rhus typhina (staghorn or velvet sumac) taking a while to flower and fruit. If you don’t have flowers on more than one of your three plants, you are not likely to get fruit (unless your flowering plant is female and someone nearby has a male, in case your other two are also female). Rhus typhina and Rhus glabra (smooth sumac) are dioecious, meaning that they produce male and female flowers (yellow green upright cone-shaped panicles) on separate plants. Plants of both sexes need to be grown together, and pollen from the male flowers needs to reach the female flowers, for the the upright clusters of the fuzzy disc-shaped dark red fruit (berry-like drupes) to develop on the female plants. These fruit clusters are colloquially referred to as ‘bobs.’

You can examine the flowers on your plant closely (with a hand lens) to determine if they are male or female. Male flowers tend to be larger and have five yellow-tipped stamens, while female flowers have a three-lobed style in the center, and a calyx with five pointed lobes nearly the same length as the petals. Both flower stalks and calyx are densely hairy. [Source: Minnesota Wild Flowers field guide online] Here are additional photos to clarify the description.

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Hellebores won’t flower

One of my hellebores did not flower this year. I think the spot became too sunny with removal of a bush. When can I transplant it?

 

Hellebores should not have a problem with sun. They will do fine with a certain amount of shade in the summer, but according to C. Colston Burrell and Judith Knott Tyler’s book, Hellebores: A Comprehensive Guide (Timber Press, 2006), “the more sun hellebores receive, especially in spring while the foliage is expanding, the fuller the plants grow and the more prolifically they bloom. Light to partial shade is best for most species and hybrids. The stemmed species such as Corsican hellebore are likely to flop in shade, and they tolerate full sun.” The authors also say that it takes 2 to 3 years for plants to bloom at full capacity, so if these are new Hellebores, perhaps they are still getting settled. After 2-3 years, the number of flowering stems should increase.

Have you removed last year’s leafy growth? Perhaps if you do this, the plants will invest their energy in the flower stalks. The Burrell and Tyler book says that the winter foliage can cause problems if it becomes entangled with emerging flower scapes. Winter foliage can also attract aphids, which will drain the plant’s energy as well. Be careful when removing the old leaves, as the sap can cause skin irritation.

If you wish to move the plants, I would suggest waiting until summer or fall when they are dormant. Moving them might mean you won’t get flowers for a while, until the plants settle into new surroundings.

When transplanting, Burrell and Taylor indicate that “Small plants that are not root-bound recover from transplanting fairly rapidly.
Once planted, sparse to moderate blooming occurs the following season. It takes
two to three years for plants to reach full steam.” p. 162.

Also, be sure that if you move it you replant it at the same depth it was growing at before, since deep planting can prevent flowering:

“Hellebores buried with their crowns in
the soil exhibit inferor flowering, if they bloom at all, though they continue
to produce foliage. The crowns produce short vegetative stems that raise the
leaf buds up to the soil surface, but in our experience, when buried alive
seldom flower.” p.167

It is always hard to know the precise reason a plant fails to produce flowers, as there are many possible causes. I recommend removing the winter leaves, and waiting to see if the flowers return next year. I would not move the plants just yet, unless the site has become scorchingly hot.

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Snowdrop buds won’t open

I planted some Galanthus ‘Flore Pleno’ three years ago. For all three years, the foliage comes up, buds form…..and then nothing. The buds swell and begin to color, but they never ‘drop,’ and will remain on the plants for up to two months without change. They never open, but very gradually become desiccated. They do not turn brown like daffodils with bud blast, and I see no signs of fungal disease. The foliage appears totally healthy. They are planted in a north facing bed, soil is medium-heavy but not waterlogged. I have done research but have found no explanation. Any thoughts are appreciated.

 

A general article by Christopher Lloyd on snowdrops in The Guardian (2001) makes a brief mention of heat causing bulbs to go blind (i.e., not flower), but this is said in the context of growing them indoors. Lloyd also mentions that Galanthus bulbs “are at their happiest in a clay/humus-rich soil that will be damp in winter and spring and dry during the summer.” They do not thrive in soil which is too rich or too acidic.

Another possibility is that you may need to divide them. Seattle’s Dunn Gardens has a helpful care sheet for growing snowdrops. Here is an excerpt:
“In the garden snowdrops do best in a partially shaded situation. If you have a very sandy, free-draining soil, amend it with compost. They love damp ground especially in the winter/spring. After the plant has finished flowering, allow the foliage to fully die down on its own. Do NOT cut the foliage off early, nor twist or braid it. Yes it will be ugly, but if planted around later emerging perennials, it won’t be so offensive.
“The Narcissus fly is the bane of snowdrops. After flowering, the fly will lay eggs on the foliage. The eggs hatch and the maggots will eat their way down into the bulb, destroying it. We’ve found that siting this bulb, where it gets afternoon or full shade after flowering, greatly reduces the chances of infestation. There is little in the way of chemical control, and what there is, is nasty.
“To bulk up galanthus, liquid feed after flowering, with a half strength solution of a water-soluble fertilizer, every two weeks, until the foliage has died down completely. If you
notice that the clumps are becoming congested (bulbs are starting to push up out of the ground), divide immediately after flowering.”

I recommend Naomi Slade’s book, The Plant Lover’s Guide to Snowdrops (Timber Press, 2014). In it, she describes in great detail the Fibonacci series by which snowdrops multiply: some varieties do this quickly, others slowly, in a mathematically governed sequence. The result of this natural system of propagation is that you will eventually have a dense clump of snowdrops that needs splitting up every few years if the bulbs are to have sufficient resources to produce flowers.

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Encouraging blooms on Hydrangeas

Help! We live in North Bend and have several Hydrangeas. I have a large Annabelle that
has never bloomed properly. Is there some special care or
fertilizing that I can do to encourage normal blooms on these
plants?

 

Here is some information on how to improve flowering, from the U.S. National Arboretum:

Excerpt:

“There are three possibilities for lack of flowering among the hydrangea
species. The first two too much shade and improper pruning apply to
all hydrangeas, while the other weather-related damage to flower buds applies primarily to the bigleaf hydrangea.

“While most Hydrangea species benefit from some shade, too much shade can
reduce flowering. This is particularly true of panicle hydrangea, which
is the one Hydrangea species that grows well in full sun. If you have a
hydrangea that used to bloom well but now flowers only sparsely, evaluate
whether the growth of nearby trees has reduced the amount of light that
reaches the hydrangea. If so, you may want to consider moving the
hydrangea to a sunnier location.

“Improper pruning can also reduce flowering in Hydrangea. Since bigleaf
and oakleaf hydrangeas flower on previous year’ s growth, potential
flowers buds would be removed if the plants were pruned in fall, winter
or spring. Panicle and smooth hydrangea flower on this year’s growth, so
pruning them in early summer would reduce or eliminate flowering for that
year.

“The most common reason for lack of flowering in the bigleaf hydrangea is
unfavorable weather. Most H. macrophylla cultivars flower primarily on
previous year’s growth. Weather conditions that damage aboveground parts
of the plant can reduce flowering. Damaging weather conditions include
early fall freezes that occur before the plant is completely dormant,
extremely low winter temperatures, and late spring freezes that occur
after the plant has broken dormancy. In USDA Cold Hardiness zone 6 and
warmer, which is the recommended growing area for H. macrophylla, the
most common of these unfavorable weather events is late spring freezes
that damage tender new growth. This is particularly true in the
southeastern U.S., where ‘see-saw’ temperatures are very common in the
spring.

“Bigleaf hydrangea responds quickly to warm temperatures in late winter
and early spring by breaking dormancy and producing new leaves.
Unfortunately, these spells of warm weather are often followed by periods
in which temperatures reach well below freezing. The severity of the
damage caused by these freezes depends on how many of the buds had broken
dormancy. If a substantial portion of the buds on a stem were actively
growing, the whole branch may die. For some cultivars, the loss of the
aboveground part of the plant will completely eliminate flowering the
following summer. The plant will produce new buds from the base of the
stems, but stems produced from these buds will not flower in these
cultivars.”

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Rhododendron won’t bloom

This is the second year in a row that my rhododendron Blue Peter has flower buds but they are dry and somewhat dark and have no flowers at all. These buds are easy to deadhead. Can you help me salvage this rhododendron, which is very old, and beautiful when it blooms?

 

In order to get an accurate diagnosis you will need to take a sample of your plant (including both healthy and affected parts if possible) to a Master Gardener clinic. If they do not know what it is, ask them to send the sample to the pathology laboratory in Puyallup. It is best to go through Master Gardeners first so you will not be charged. If you send the sample yourself there will be a fee.

Meanwhile, several sources mention frost, drought, and “bud-blast” (unlikely in the Pacific Northwest) as potential causes of bud failure. Damaged flower buds and poor bud set: It is always most disappointing when fat, healthy looking flower buds either fail to open at all or only open a percentage of their buds, the rest being black and dead. Some rhododendrons regularly abort some or even all of their buds for no apparent reason. This may be due in some cases to a deficiency, perhaps magnesium, or to drought reports from various places give mixed results from applying magnesium (usually as Epsom salts)… By far the most usual cause of bud damage is frost. Flower buds are invariably less hardy than the rest of the plant so a really hard winter is sure to cause losses to flower buds. Early autumn frosts can damage buds that are not fully hardened off. This is a very annoying type of damage that may be overlooked and may not be noticed until the buds attempt to open in spring. Rhododendrons vary greatly in their ability to harden up enough to withstand early frost. In areas very prone to spring frosts, it is better to avoid growing plants that always burst into growth at the first sign of spring. Plants that frequently loose their first growth flush (and sometimes even their second) are liable to become stunted and rarely flower.

Source: The Cultivation of Rhododendrons, by P. Cox, 1993, p. 244.

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Lilacs and failure to flower

I have a lilac bush given to me as a gift 13 years ago. I
don’t know the variety but the leaves look slightly different from the
common lilacs I see. This bush has healthy looking leaves and while it
has slowly put on growth over the 13 years it has never bloomed. I have
tried adding ashes to the soil to make it more alkaline but nothing seems
to work. What is the problem and how can I get this bush to bloom?

There are several reasons lilacs may fail to flower. Here is an excerpt (no longer available online) from North Dakota State University Extension horticulturist Ron Smith in
answer to a question similar to yours:


Lilacs fail to flower because of insufficient sunlight, planted too
deeply, too much nitrogen, improper pruning or winterkill of the flower
buds. You said the lilacs get plenty of sunlight, but unless you used a
lawn fertilizer to provide nutrients, it isn’t likely too much nitrogen
is the problem. If you planted too deeply, pull some of the soil back so
the top of the roots are slightly exposed. If you pruned in July, then
doing so removed the flower buds for the next growing season. If winter
killed the flower buds, then hope for milder winters or purchase hardier
lilacs.

Colorado State University Extension’s article, “Renewing Lilacs,” (no longer available online) offers other suggestions, such as late freezes, decreasing sunlight, and pest problems.

Sunset’s Western Garden Book (2001 ed.) says that annual pruning is
needed for optimal flower production. Most lilacs bloom on wood formed
the previous year, so they should be pruned just after flowering. Remove
the spent blooms and cut back to a pair of leaves. There are a few lilacs
which bloom on new growth, so it might be useful to know exactly what
type of lilac you have. You could send photos or bring in samples for identification.

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Hydrangeas won’t bloom

I have two Hydrangeas growing up the side of my house in a northeastern exposure. This will be their 4th year. Leaf growth is robust… flower growth almost non-existent (on one of the shrubs, one bloom last year; one forming this year). What can I do to encourage bloom or should I start over?

According to the Plant Addicts website, there could be several reasons why yours are not blooming well. Check out their page, “Why Won’t My Hydrangeas Bloom?”

There is another useful resource that may be of help. Try Why Plants Fail to Bloom, by Leonard P. Perry, a professor at the University of Vermont Extension. Perry suggests there are five possible reasons: Age, Temperature, Alternate Flowering, Light, Nutrition and Pruning.

In addition, I consulted two books on hydrangeas. Both mentioned that Hydrangea anomala subsp. petiolaris can take time to bloom. According to Michael A. Dirr’s Hydrangeas for American Gardens, Time is [the climbing hydrangea’s] biggest ally. That is, once it gets established, there is no stopping it.

Michael A Dirr. Hydrangeas for American Gardens. Timber Press, 2004. p. 24.

Toni Lawson-Hall’s Hydrangeas: A Gardener’s Guide also says that Hydrangea anomala subsp. petiolaris “grows well on north-facing walls but takes a while to get established.”

Toni Lawson-Hall. Hydrangeas: A Gardener’s Guide. 1995. p. 81.

You are probably wondering how long a while is. Alas, I was unable to locate a specific timeframe for when you might expect those gorgeous blooms to start, but from what I can gather, time may help.

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Peony not blooming

I have a peony that failed to flower this year. What could be the cause of this?

Cindy Haynes of Iowa State University of Extension has a helpful list of possible reasons peonies may fail to flower. If there are no buds, it may be due to: not enough sun; recently transplanted; planted too deeply; too much fertilizer; need to be divided (clumps too big); plants immature; premature removal of foliage (in July or August). If they have buds that don’t open, these may be the reasons: late freeze; other extreme weather; fungal diseases; insects; undernourished.

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