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Plant Answer Line Question

Keywords: Hydrangea

I have had a climbing hydrangea for 4 years - but it has never bloomed. It is growing but does not produce any buds. It gets full sun and is in good soil. What can I do so it will produce blossoms?


I looked in a few books (including Trees and Shrubs for Pacific Northwest Gardens, 1990, by Grant and Grant) about climbing Hydrangea (Hydrangea anomala ssp. petiolaris) and they all said this vine is wonderful and robust but very slow to establish. You may just have to wait a few more years.

This hydrangea prefers a cool, moist root run so be sure to irrigate it in the summer and place a good mulch (such as compost or wood chips) a few inches deep. The mulch should not touch the trunk of the vine at the top of the soil around the vine. Established trees and shrubs don't generally need feeding. Avoid using a fertilizer that is high in nitrogen, or it may add lush, green growth at the expense of flowers.

Here is additional information, from Virginia Cooperative Extension:
Excerpts: "Climbing hydrangeas only bloom on vertical stems so vines growing on the ground will not bloom. Minimal pruning is required. They bear lacecap inflorescences with an outer ring of showy white sterile florets around creamy to yellow fertile flowers in late spring. Deadheading can be done right after flowering to save energy and for aesthetics by cutting the inflorescences off above the first leaf. Branches that extend out far from the climbing surface may also be pruned back in summer after flowering to prevent the plants from being pulled from their structures by heavy winds, ice or snow."
Reasons for lack of flowers on various species of Hydrangea:

  • Improper shearing and renewal pruning on H. macrophylla and serrata cultivars
  • Frost injury to early expanding growth buds
  • Pruning more than a month after bloom time in summer
  • Excessive shade
  • Excess nitrogen fertilization

Date 2017-05-10
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Plant Answer Line Question

Keywords: Plant care, Hydrangea

I am attempting to find detailed plant information on a variety of hydrangea called Hydrangea macrophylla 'Miss Belgium', and can find very little in my plant books and online. Do you have any suggestions? Some of the details I am looking for are flower shape and size, plant habit, height & spread, and foliage details.


I found some information about Hydrangea macrophylla 'Miss Belgium' in Glyn Church's book, Hydrangeas (Cassell, 1999):

An excellent pink in alkaline soil or in containers. The plant is ideally suited to pot and tub culture as it stays small and compact (3 ft.) and the rounded heads tend to be tiny, keeping the flowers in proportion to the bush. Its free-flowering habit and healthy nature are its good qualities. It is not the best plant for acid soils as the flowers will be a strident purple-blue.

There is a photograph of 'Miss Belgium' in Corinne Mallet's Hydrangeas: Species and Cultivars (vol .1).

Heritage Hydrangeas' website has this description: "Bright magenta-red on neutral soils or purplish blue on acidic soils, the centre of each floret is always white. Impressive flowers on a compact shrub."

Date 2018-06-14
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Plant Answer Line Question

Keywords: Plant diseases--Diagnosis, Hydrangea

Why are the leaves of my oakleaf Hydrangea turning brown around the edges and falling off?


We do not diagnose plant problems, especially without a sample. It might be wise to bring a sample to your local Master Gardener clinic. You can locate a Master Gardener Clinic within Washington State here.

However, based on my personal experience with my own oakleaf Hydrangea (Hydrangea quercifolia), it is a semi-deciduous shrub that will hold on to its leaves through winter, only to replace them with fresh growth in the spring. All my Hydrangea's old leaves have turned reddish-brown and look very ratty. Once new growth resumes in spring, I cut off most of the tattered leaves. (Don't do it too early, in case there is a late frost.)

If you have new growth, do not worry about your shrub, but if you do not have new growth or it is the new growth that is turning brown then you should take a sample leaf into one of the Master Gardener clinics (linked above).

Date 2017-08-15
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Plant Answer Line Question

Keywords: Hydrangea, Fertilizers

I have a few Hydrangeas that have not been doing their best. I think I have the exposure down, and their colors. I need advice on what fertilizer is best for them and when, how much and how often to apply it. I try to stay as organic as possible.


According to Hydrangeas: A Gardeners' Guide by Toni Lawson-Hall and Brian Rothera (Timber Press, 1995), hydrangeas do not generally require special feeding. If you wish, you can apply a general fertilizer twice a year. "As important as feeding, and in fact another method of supplying nutrients, is mulching." The authors suggest using mature compost or leaf-mould. Mulching in the spring to a depth of about 3 inches will help protect the roots of your hydrangeas from drying out (but never put mulch directly up against the base of your shrubs). Mulching also suppresses weeds. Since you garden organically, mulch may be your best bet for supplying a slow and gentle dose of nutrients. If the plants continue to fare poorly, you may want to do a soil test to see if there is some kind of nutrient imbalance that needs correcting.

Date 2017-12-09
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Plant Answer Line Question

Keywords: Failure to flower, Hydrangea

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 Hydrangeas! Hydrangeas! 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.

Date 2018-04-11
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Plant Answer Line Question

Keywords: Berberis, Trachelospermum, Euonymus, Taxus baccata, Screens, Thuja, Nandina domestica, Hydrangea, Ilex, Hedges, Clematis, Buxus, Bamboo

Could you recommend some plants for a privacy screen that are also narrow? These would be planted in front of a fence in our backyard.


Here is some general information on plants for creating a screen.

Trees for Problem Landscape Sites -- Screening from Virginia Cooperative Extension

Good Hedges Make Good Neighbors from the Humane Society

Bet on Hedges by local garden writer Valerie Easton.

Here is a list of narrow plants for a screen from local garden designer Chris Pfeiffer:

Fastigiate shrubs for naturally narrow hedges. Compiled by Chris Pfeiffer. 2005.

Zones 5-6:

American arborvitae 'Rheingold' (Thuja occidentalis 'Rheingold') 5'h x 3'w

Barberry 'Helmond Pillar' (Berberis thunbergii f. atropurpurea 'Helmond Pillar') 6'h x 2'w

Boxwood 'Graham Blandy' (Buxus sempervirens 'Graham Blandy') 8'h x 1-1/2' w

English yew 'Standishii' (Taxus baccata 'Standishii') 4'h x 1-1/2' w

Irish yew (Taxus baccata 'Fastigiata') 20' h x 4' w

Japanese holly Jersey pinnacle (Ilex crenata 'Jersey Pinnacle') 6' h x 4' w

Japanese holly Mariesii (Ilex crenata 'Mariesii') 3' h x 1-1/2' w

Zones 7-9, in addition to the above:

Dwarf yeddo rhaphiolepis (Rhaphiolepis umbellata Gulf GreenTM) 3-4' h x 2' w

Heavenly bamboo 'Gulf Stream' (Nandina domestica 'Gulf Stream') 4' h x 2' w

Japanese euonymus 'Green Spire' (Euonymus japonicus 'Green Spire') 15' h x 6' w

You might also consider installing a trellis to increase the height of the fence, and then growing an evergreen vine such as Clematis armandii, evergreen hydrangea (Hydrangea seemanii), or star jasmine (Trachelospermum jasminoides).

This link is also helpful (scroll down to "Evergreen Vines" and look for appropriate height and light requirements).

You could grow bamboo, but I would recommend growing it in a container, or a series of containers, as you do not want the roots to spread. I have seen an effective bamboo screen between two houses growing in a long rectangular lined wooden trough (lined with bamboo barrier). Some species of bamboo are more tolerant of partial shade than others. Look for a clumping, rather than a running, bamboo (like Fargesia) to be on the safe side.

Growing Bamboo in Georgia

Running and Clumping Bamboos

Bamboos for hedges or tall privacy screens

Date 2018-04-11
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Plant Answer Line Question

Keywords: Failure to flower, Hydrangea

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:


"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."

Date 2018-04-11
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Plant Answer Line Question

Keywords: Planting, Hydrangea

I would like to plant hydrangeas along a south-facing shed. The site gets some morning sun and quite a lot of afternoon sun from over the roof of the house. This area currently has moss growing on it and has not been previously used for planting. Your reply will help me to decide whether to plant there or not.

I have amended the area where I have planted the hydrangeas with chicken manure and compost. I dug holes about 14 inches deep and and about 14 inches square. I also put a spade full of gravel at the bottom of the hole to improve drainage as I suspect that the base soil is mostly clayey.


Most hydrangeas will do well in sun to part shade although full sun in a hot climate would be too much. You also want to bear in mind that hydrangeas, especially Hydrangea macrophylla, prefer adequate moisture. According to Michael Dirr's Hydrangeas for American Gardens (Timber Press, 2004), an inch of water once or twice a week should be sufficient as long as the plant's soil needs are met (consistently moist, well-drained, acidic soil which is rich in organic matter such as leaves, compost, well-aged manure). Some species of Hydrangea tolerate heat better than others, according to Dirr. Hydrangea macrophylla, H. serrata, and H. umbellata do not fare as well as H. paniculata. Some species, like H. quercifolia and H. aspera, prefer shadier spots. Dirr recommends using drip irrigation for plantings of Hydrangea, specifically using drip tubing, extender lines, and emitters attached to a garden hose, possibly with a timer.

The Michael Dirr book says that good soil preparation (not just of the planting hole) ahead of time is the best thing for hydrangeas. He does not subscribe to the rule sometimes put forth, that the hole must be 3 times as wide as the root ball. I also consulted Hydrangeas: A Gardener's Guide by Toni Lawson-Hall and Brian Rothera (Timber Press, 1995) which says the hole should be 2 times the rootball's width and depth. Be sure to check the state of your plants' roots. You want to make sure they are not coiled in a spiral or restricted in any way. You may need to tease out or prune the roots a bit before planting.
Professor Linda Chalker-Scott discusses planting procedures in her book, The Informed Gardener (University of Washington Press, 2008), advising that the planting hole only needs to be the depth of the root system, but twice the width. She also recommends against amending the planting hole in any way. Backfill the hole with native soil, not a soil amendment. The idea is not to 'spoil' the plant by putting rich compost just in the hole, which will deter the roots from spreading out into the surrounding area. Here is more of her writing on this subject.

You have already amended the surrounding soil, so the addition of gravel to the hole is not necessary, and is possibly not a good idea, according to general planting information from University of Minnesota Extension. Here is an excerpt: "If soil drainage is inadequate, species that are tolerant of poorly drained soils may be planted, or soil drainage may be improved. This can be done in two ways. If a hard pan is present (a compacted, impermeable layer of soil) with an underlying layer of well-drained soil, a hole can be dug down to the permeable layer to provide drainage for the planting hole. If the soil is poorly drained and there is no well-drained layer below, a tile system can be laid. This, however, is expensive and requires the assistance of a professional for proper design. Simply adding gravel to the bottom of the planting hole will further decrease oxygen availability to the root system."

Date 2017-08-15
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Plant Answer Line Question

Keywords: Pruning, Hydrangea

It's January, and my hydrangeas look terrible. When should I prune them?


The answer will depend on which species of hydrangea you are growing. According to the American Horticultural Society Pruning & Training edited by Christopher Brickell (DK Publishing, 1996), Hydrangea macrophylla (big leaf or mophead hydrangea) should be pruned after flowering in warm climates but in colder climates it is best to leave the old flower heads on the plant over the winter, and prune in spring. This rule also applies to Hydrangea serrata. If your hydrangea is blue-flowered, it is probably H. macrophylla. In her Guide to Pruning (Sasquatch Books, 2006), local pruning expert Cass Turnbull of Plant Amnesty says this plant should not need much pruning, but if you want to remove the faded blooms, you can do this in February by looking for four or five pairs of plump buds below the old flowers, and cutting just above the lowest or second lowest set of buds.

Hydrangea paniculata should be pruned in early spring, before active growth begins.
Hydrangea arborescens needs little pruning, and any pruning at all should be done in early spring.
Oakleaf hydrangea (Hydrangea quercifolia) also needs little pruning, but may be pruned in spring.

>The U.S. National Arboretum offered a good introduction, no longer available on their website, but excerpted here:
"Established bigleaf, panicle, oakleaf and smooth hydrangea plants can often benefit from regular pruning. Removing about one-third of the oldest stems each year will result in a fuller, healthier plant. This type of pruning is easiest to do in winter, since the absence of leaves makes it easier to see and reach inside plants.
Gardeners may also want to prune to control height or to remove old flower heads. The best time for this type of pruning differs between species. Bigleaf and oakleaf hydrangea, which flower on previous year's growth, should be pruned shortly after flowering is complete. Panicle and smooth hydrangea flower on current year's growth and can be pruned anytime from late summer until early spring. If pruning these two species in the spring, try to prune before leaves appear. Plants of H. arborescens 'Annabelle' have been known to produce a second flush of flowers if pruned lightly after the first flowering.
Stems of bigleaf hydrangea that have been damaged by cold should be pruned as soon as it is determined that they are dead. Watch for new growth at the base of the plant. If your plant has basal shoots that are 6 to 8 inches in length, but the upper parts of the stems are still bare, then the bare stems need to be removed. For bigleaf hydrangea plants that are subject to frequent weather-related dieback, other than removing the dead stems, you probably won't ever need to do any other pruning--Mother Nature has been doing the work for you."

Kitsap County Master Gardener Peg Tillery, in an article formerly available on the WSU Extension Kitsap County web site, recommends waiting until March to prune hydrangeas: "In our climate we need to wait until early March to prune roses and summer blooming hydrangeas. This way the tender new growth won't be harmed by frosts."

The Royal Horticultural Society provides general pruning recommendations.

Here is an excerpt from a Seattle area gardener's response to a question about hydrangea pruning on Garden Banter, a British gardening forum:
"Different species of hydrangeas have different criteria for pruning. Some need very little pruning at all,other than to shape, as with H. quercifolia and H. anomala petiolaris. H. arborescens does well with the dramatic pruning you describe. Pruning of H. paniculata would depend on if you were training it to be upright like a tree or as a broad shrub, and need not be dramatic pruning, just barely enough to induce new growth on which flowers occur, though in your zone a more dramatic pruning might be needed because of winter damage. Most hydrangeas prefer late winter pruning, but H. macrophylla is better done in late summer when flowers are getting scruffy and new shoots are developing."

Date 2018-04-21
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Plant Answer Line Question

Keywords: Vegetative propagation, Transplanting, Hydrangea

I have a very large hydrangea that has been in the ground at least 15 years. I'd like to move it, and have heard that it can be divided into several bushes. Are there any special details I should consider when performing this task?


I found a reference to the technique you describe in Hydrangeas: A Gardener's Guide by Toni Lawson-Hall and Brian Rothera: "DIVISION. Sometimes, when moving a large H. macrophylla cultivar, the plant falls apart during the operation. It has been found that, provided each section has good roots, planting the separate pieces is totally successful." This is similar to the process of layering, where branches are nicked and then pinned down into the soil to allow roots to form, and then severed from the parent plant with a sharp shovel six months to a year later. The small plants will be genetically identical to the original plant.

Date 2018-03-14
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Plant Answer Line Question

Keywords: Flower color, Hydrangea

Is the color of every type of Hydrangea variable, according to the pH of garden soil? Or are some species or varieties reliably the same color, no matter where they are planted?


I think the main species of Hydrangea whose color gardeners sometimes try to alter is Hydrangea macrophylla, also known as hortensia, bigleaf, or mophead hydrangea. According to Van Gelderen's Encyclopedia of Hydrangeas (Timber Press, 2004), most cultivars of Hydrangea macrophylla are naturally pink, even in slightly acidic soil. "The key factor in flower color is not the acidity of the soil, but a plant's accessibility to aluminum sulfate." The plant will not produce blue flowers if it has access to aluminum sulfate but the soil is strongly alkaline, as the calcium of high pH soils will bind with it, preventing the plant from absorbing it. The authors state that "some cultivars easily turn blue under the right conditions," while others do not. White-flowered cultivars of different Hydrangea species usually retain their color, though the flowers may become flecked with red or pink toward the end of the season.

Hydrangeas: A Gardener's Guide, by Toni Lawson-Hall and Brian Rothera (Timber Press, 1995) says that while several species of Hydrangea may have some variation in color, Hydrangea macrophylla ssp. macrophylla and its cultivars (including mopheads and some of the lacecaps) have potential for the most dramatic changes. However, "there are some innate preferences within the individual plants [...] and not every mophead or lacecap will change colour in response to a gardener's alchemy." The authors do mention a few plants which display red flowers even in acid soil, such as cultivars of Hydrangea serrata: 'Preziosa,''Grayswood,' and 'Beni-Gaku.' Among the H. macrophylla cultivars that stay red in acid soil are: 'Alpengluhen,' and 'Altona.' Cultivars which are considered most reliably blue on acid soil also need a low level of phosphate: H. macrophylla ssp. macrophylla 'Gentian Dome' and 'Marechal Foch' (both deep blue), 'General Vicomtesse de Vibraye' (pale blue), and Hydrangea serrata 'Diadem' and 'Blue Deckle' (blue lacecaps).

You may find information from the U.S. National Arboretum on this topic useful.

Date 2017-07-18
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Plant Answer Line Question

Keywords: Schizophragma hydrangeoides, Hydrangea

There's a climbing vine in my garden which has hydrangea-like flowers. I have lost the tag, and don't know if it is Hydrangea petiolaris, or Schizophragma hydrangeoides--how can I distinguish one from the other?


There is an article in Arnoldia (the journal of the Arnold Arboretum at Harvard University) from July 24, 1933 which explains that the two plants are related, but the flower 'petals' (which are actually sepals) surrounding the center are distinct:
"In Hydrangea petiolaris this encircling tiara is composed of greenish white flowers, each one made up of four rounded sepals. In Schizophragma hydrangeoides these showy sepals are a purer white and they are borne singly rather than in fours."

University of Arkansas Extension also says that Schizophragma "differs in flowering time (after climbing Hydrangea) and in the fact that it protrudes less from structures."

There is another less commonly grown climbing Hydrangea, Hydrangea integrifolia, an evergreen that grows to 40 feet tall and 20 feet wide. Its flower buds look almost like those of peonies, and its leaves are elongated and glossy.

Date 2018-03-15
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Garden Tip

Keywords: Rosa, Garden design, Amelanchier, Sedum, Hydrangea

It's easy to plant a garden that is colorful and interesting in June, more difficult is designing a garden that shines in October. Read Autumn Gardens by Ethne Clark (Soma, 1999) to learn both design principles and the best trees, shrubs, perennials, bulbs and grasses to plant in fall. Oakleaf hydrangea, Canadian serviceberry, species roses, and sedums are just a few of the plants featured that will extend the garden interest beyond Labor Day.

Date: 2007-07-13
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May 31 2018 13:14:08