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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

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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Vine maple fall foliage

I have a vine maple tree whose leaves turn a very plain, rather ugly brown in the fall. It gets full sun from about noon until sunset. From what I have read, its leaves should turn red, orange, and yellow. What can I do to trigger this? I am thinking of how Hydrangeas are different colors depending on the acidity of the soil. I would like a tree with attractive fall color. I have also read it likes moist places in the shade, and it has not had that environment in my yard. Could the amount of water it gets in the summer, or lack of water, be affecting this?

 

According to J. Harris in The Gardeners Guide to Growing Maples (2000, p. 119),
“Autumn color is due to a chemical change in the leaves and a combination of the
remains of the chlorophyll grains and a substance called anthocyanin. The
color assumed by leaves depends on soil and air conditions and on the amount
of moisture. If conditions are very dry in the autumn, then the color will
not last for long. After a frost, colors appear more intense, but the frost
can check activity. It will also not be so good in very wet conditions.”

The National Arboretum provides a complete explanation of why autumn
leaves turn color.

There is an excellent article from the Seattle Times (September 25, 2008) in which former Washington Park Arboretum Collections Manager Randall Hitchin describes this process. Fall leaves change color during “the final stage in the life of a leaf. [This] has to do with four groups of pigments. You know about chlorophyll, the green chemical that does all the heavy lifting spring through summer. Then there are the carotenoids — carotene and a suite of related compounds — that give leaves yellow and orange coloring. Tannins produce the russets and browns. Finally, anthocyanin provides the classic autumn colors of red and purple. During the growing season, chlorophyll dominates. It’s constantly being made to replace what’s degraded by ultraviolet light, and the leaf appears green. Depending on tree species, yellow, orange or brown pigments have been there all along, concealed by green chlorophyll. In autumn, as chlorophyll production slows and ultimately stops, the yellows, oranges or browns emerge. Anthocyanin is genetically controlled, so some tree species get red and some can’t. Unlike the carotenoids, anthocyanin isn’t usually present during the growing season, but is produced in leaves with fall weather conditions. In trees that can go red, the amount of it depends on environmental factors. In ideal conditions, you see vivid pinks, reds and purples — that ooh-and-ah factor. […] The Northwest autumn is often overcast or rainy with only minimal cooling at night; not optimal for fall color. Another reason has to do with numbers. In the Northwest, the effect of color is diluted because of species composition in our forest canopy, which is typically dominated by evergreens. With the evergreens outnumbering the changing deciduous trees, you don’t get those huge sweeps of colors you see back east.”

There are other possibilities why your vine maple is not producing good fall
color:

1. It might be getting too much light. The natural habitat for the vine maple is
under an overstory of large conifers (Japanese Maples, by J. Vertrees,
2001, p. 247). Afternoon sun is the most intense and could be stressing the
tree. Harris (2000) notes that while tree-like species prefer open sites, woodland conditions and dappled shade are ideal environments for shrubby maples. (Harris., p.
118).

2. Other than light, the environment might be a little off. Vertrees (2000, p. 247) notes that with vine maples, intense color does not develop in environments where abundant moisture and fertility keep the trees from being under stress, i.e., they need stress to produce good color.

3. Trees of the same species will exhibit different fall colors depending
on the growing environment and peculiarities of each individual tree. (As
identical twins can be quite different). When selecting a tree for fall
color, it is best to first view it in autumn — then remember it will change
somewhat when it is installed in a new home.

It is not likely that changing soil pH will have an effect. I have been
disappointed in fall color a couple of times and finally replaced the
trees — after viewing them in full color in the nurseries.

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Honeydew and sooty mold

This is both a plant and insect question. I manage a property that has a small stand of planted English and Garry oaks. This summer, there has been a very large population of bees and yellowjackets attracted to these trees. There isn’t a nest or hive on the 5 acre property that I have found, so these bees seem to be coming in from a distance. Indicators that I am observing are:
Many sap (sucker) holes on these trees, one in particular.
A heavy black dusty coating on most of the leaves.
The sound of droplets, not humming or eating.

 

Based on your description, my first thought is that the coating on the leaves sounds like sooty mold. First comes the sticky honeydew left by leaf-sucking insects such as aphids, and then the sooty mold develops on the sticky substance. It would make sense that bees and wasps might be attracted by the honeydew, but might also be preying on the smaller insects that cause it.

This article, which comes from a beekeeping perspective, may also be of interest. Here is an excerpt:
“Although it may be off-putting to think of eating insect excrement, honeydew honey is prized in parts of Europe and New Zealand and often fetches higher prices than floral honey. It is rich in mineral content, amino acids, and may have stronger antibacterial properties. When a psyllid insect or aphid ingests the plants sap, it digests the small amount of protein present and expels the rest of the water, sugars, tannins and other indigestible material as honeydew. If you have ever parked your car under a tree and found it covered in a sticky substance the next morning, chances are the tree is infested with sap-sucking psyllids or aphids. For many other insects including ants, wasps, and bees, this is a valuable food source.”

Your poetic description of “the sound of droplets, not humming or eating” might be the sound of transpiration from the leaves, or just the honeydew (part tree sap, part insect excrement) seeping from them.

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Fragrant Hydrangea

I want to add a hydrangea to my garden but I would prefer one that is also fragrant. Are there varieties that have a noticeable pleasant scent?

 

There are some species and cultivated varieties of Hydrangea that are reported to be fragrant. Bear in mind that everyone’s sense of smell is different. I recommend seeking out examples when they are in flower and doing a sniff test in nurseries, gardens, or large parks and arboreta with a good selection. The ones that have a fragrant reputation are:

  • Hydrangea quercifolia: the smell is a rich honey-vanilla to my nose. This shrub is also a wonderful magnet for honeybees, bumblebees, pollen wasps, and syrphid flies. Its inner flowers are fertile, while the more dramatic outer sepals are sterile. Cultivated hydrangeas have been bred to emphasize the sterile florets, while wild hydrangeas tend to have fewer of these and are more useful for pollinators. In my garden, all the pollinator activity is humming along on the fertile inner flowers beneath those sterile four-petaled parts of the inflorescence. The showy parts of a hydrangea so prized by humans for their beauty are not what interests the pollinators .
  • Hydrangea angustipetala and its cultivar (‘Golden Crane,’ also called ‘MonLongShou’): said to smell strongly like jasmine or sweet alyssum; of the species, Dan Hinkley says: “The deeply scalloped sepals of the infertile florets surround a disk of striking chartreuse fertile flowers while emitting a faint but beguiling fragrance.” [Horticulture, Jun/Jul2009, Vol. 106, Issue 5]
  • Hydrangea scandens: Dan Hinkley says: “As its name implies, it can be a sprawling shrub but far from what would be considered disheveled. The branches possess a pleasing burgundy-brown color and the lacy cream-colored flowers pack a powerful fragrance during March and April. Hydrangea scandens ‘Fragrant Splash’ adds a bonus of variegated foliage.” [Ibid.]
  • Some hybrids of Hydrangea macrophylla x Hydrangea angustipetala
  • Hydrangea macrophylla ‘Ayesha’: “one of the only Hydrangeas to have a delicate fragrance in bloom” [Great Plant Picks profile]
  • Hydrangea anomala ssp. petiolaris (a climbing hydrangea)
  • Hydrangea paniculata: “slight floral scent” or “mild fruity fragrance”

Close relations in hydrangea family:

  • Pileostegia viburnoides: “In late summer, frilly cymes of heavily-scented flowers erupt amidst its foliage, filling the air of our woodland drive with a delicious aroma of honey. Not surprisingly, honey bees are highly attracted to the flowers that rely entirely on scent.” [Heronswood blog, August 29, 2018] However, not all noses smell alike. An article in Arnoldia [June 2, 1964] says “The floral odor is described as ‘fragrant’ or ‘ill-smelling.'”
  • Decumaria barbara (woodvamp): a climber in the Hydrangea family, native to swampy areas of the southeastern U.S., with fertile flowers that are slightly fragrant or fragrant, depending on the source.

Based on the research above, Hydrangea quercifolia and Hydrangea angustipetala cultivars seem like the best choices.

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Spitting Rhododendrons

Why are my rhododendrons spitting water? On hot sunny days this summer, we’ve been sitting in their shade and noticing occasional tiny needle-fine droplets landing on us. Is this caused by insects (I don’t see obvious signs of them on the leaves), or is it normal?

 

My hunch is that the leaves are transpiring. I found an article by Bill Letcher in the Journal of the American Rhododendron Society (vol. 41, no. 2) entitled “Rhododendrons with a Drinking Problem.”

The article is about the importance of water in successful rhododendron cultivation, but also does a good job of explaining transpiration:
“The water absorbed by the root hairs, or rootlets, is drawn up in the stem of the plant and into the leaves, where it exits via small holes called stomata into the air as vapor. This process is called transpiration […] Transpiration requires a lot of energy, and this comes, as we might expect, from the sun. If all else is equal, transpiration amounts are directly proportional to the amount of radiant energy striking the leaf surface of a plant: the more energy, the greater the amount transpired. […] One factor of paramount importance to rhododendron growers which effects transpiration is the relative humidity of the air surrounding the leaves. Dry air causes appreciably more transpiration than humid air, and the presence of wind increases this dramatically by replacing the layer of air next to the leaf surfaces before it can become saturated. Ambient air temperatures will also markedly increase transpiration as they rise, sometimes with disastrous results. Our family of rhododendrons has less ability to extract moisture from the soil than, say, manzanita (which can pull all of the available water from the soil down as far as six feet!).”

If we have more hot weather, you may want to give your shrubs an occasional supplemental drink of water, since they are shallow-rooted, and our summer-dry climate (depending on how hot and dry it is) can cause stress to the plants. Keep an eye on how they are looking and do what you can to maintain their health (and preserve your shady refuge!). To quote Letcher again:
“The family of rhododendrons has either never been forced to adapt to very low available moisture conditions, or has not adapted well to them. Their roots tend to be quite shallow. The foliage is lush, dense, and of a dark, absorptive color instead of being light and reflective of the radiation. They display their displeasure with your attempts to wean them from the conditions they most enjoy, by doing exactly what a great many other plants will do: they shorten their internodal growth, reduce the number and size of their new leaves, drop some of their older leaves, and just plain sulk! Ultimately, they languish into a pitiful state of scrawnyness and pallor which is not a pleasant sight in your garden.”

 

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Apple blister mites

For a few years, our Liberty apple has developed tiny pouches on its leaves. Soon, the leaves turn yellow and drop prematurely. It also seems to affect the developing fruit with dimpled dark spots.

 

It sounds like your tree has apple blister mites, a type of eriophyid mite. They are tiny, and you would need a magnifying lens to see them. There is information about this mite in the Pacific Northwest Insect Management Handbook, including life cycle, and methods of control with dormant sprays (some of which are accepted for use in organic orchards). The mites overwinter under the outer bud scales on the tree. In case you are wondering where to look for bud scales, when the tree loses its leaves in fall or winter, bud scales form at the ends of branches or stems. The bud scales protect new growth that will emerge here. When buds swell in spring, the mites will burrow into them to feed. Once the blossoms have fallen, they will progress to leaves and developing fruit.

Mites are attracted to drought-stressed trees, and to nearby weeds like clover, mallow, bindweed, and knotweed. They can be carried from tree to tree by wind or birds and other insects. Usually, ample rain and cold winter weather keep mite numbers down, but as the climate changes, we may be creating conditions that are more favorable to them.

You might be able to find a source for predatory mites to help control the blister mites. Washington State University’s Tree Fruit research site describes several species of phytoseiid predatory mites.

About Smilax bona-nox

Can you identify a plant growing at my mother’s house in Georgia? We would like to know more about it.

 

This is Smilax bona-nox. It goes by many evocative names, and even the scientific name had me wondering. Why is the species name “good-night?” It was named by Linnaeus and in his time bona-nox would have served as a euphemistic Latin curse (the way someone might say dadgummit, goldarnit, or flipping heck), possibly uttered after getting ensnared in this viny plant’s thorns. According to Delena Tull, author of Edible and Useful Plants of Texas and the Southwest (1999 ed.), encounters with the curved prickles give rise to common names like catbrier (or catbriar) and blaspheme-vine. Other common names include saw greenbrier (or saw briar) and tramp’s trouble. It is also called zarzaparilla (Anglicized to sarsaparilla from the Spanish name which means bramble + little grape vine).

According to the Virginia Native Plant Society, the fruit of Smilax species is valued by birds, bears, foxes, possums, and squirrels. The flowers are nectar and pollen sources for bees and flies, and the leaves host the larvae of caterpillar moths. The Native American Ethnobotany Database lists medicinal uses of this species of Smilax by the Seminole, Choctaw, Houma, and Creek tribes. The Choctaw and Houma ground the dried tuberous roots into flour for use in bread and cakes. The Comanche used the leaves as cigarette rolling papers.

About the common name sarsaparilla, you may be familiar with this word as flavoring sometimes used in the beverage known as root beer. A traditional tonic made with the rhizomes was thought to ward off rheumatism. Both Smilax and Sassafras have been used in flavoring root beer, but Sassafras root bark contains safrole, a carcinogenic substance, and the Food and Drug Administration banned its use in food in 1960. There is now a safrole-free extract that is allowed in food.

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Artificially painted living plants

My alliums are done flowering, and the stalks look like straw. Can I spray-paint the flower heads now, or will it damage the plant below ground?

 

There are more natural and nontoxic ways of sustaining colorful garden interest. They involve planning and selecting plants that flower at different times throughout the year. Gardens are, of course, constructed landscapes and not the same as nature. Artificially colorizing spent plant matter appeals to some gardeners’ aesthetic sense but not to others. In my own garden, the alliums are done flowering but the nearby Eryngium (sea holly) is just taking off, dotting the bed with silver and blue. Some plants provide interest even when they are desiccated and brown through the winter, and I would include allium in this group.

However, if you would like to spray color on your allium heads, there are directions here that show how to make a kind of protective dropcloth out of a heavy paper plate with a notch cut into it.

It would be good to avoid getting any paint on the ground, and I suggest not doing it on a windy day. See if you can find spray paints that have lower volatile organic compounds. Despite marketing claims, there is no such thing as a non-toxic aerosol paint as this archived article claims.

There does seem to be a trend in marketing artificially painted living plants, such as succulents which are now being sold in big-box stores. This seems a pity, since there is such beauty in the actual shades of plant foliage. Additionally, this is short-sighted, because the plant will be unable to photosynthesize and transpire, and will eventually suffocate. See the following articles from Better Homes and Gardens, and Southern Living)

Another thought: if you want to cut the allium stalks and use less toxic water-soluble paints (such as casein) to paint them and display them indoors (where rain will not wash away the coloring), that is also an option. My personal preference is to appreciate the natural color of plants as they age and decay, but again, this an aesthetic choice—just like dyeing one’s hair.

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Mushroom identification

I was in the backyard tidying up after my dog when I noticed a tiny orange mushroom growing out of the moss in the lawn. It is a fragile thing, about an inch long. The cap has a slightly darker indentation on top. Even the stem is orange, and the gills look like the fan-vaulted ceiling of a miniature cathedral and extend a short distance down the stem. I am curious to know what it is.

 

I confirmed with local mushroom experts that this is Rickenella fibula. It is fairly common in the Pacific Northwest, but seldom noticed, so good spotting! The technical description of gills that extend down the stem would be “decurrent, slightly traveling down the stipe.” Here is general information about this mushroom from Michael Kuo’s Mushroom Expert site. He mentions that it may have a mutualistic relationship with moss, and that is discussed further on the Forest Floor Narrative blog:

“Most species that occur with moss are saprobes that share similar niche requirements with the moss. That is, many of these organisms can only exist in a certain range of temperature, moisture, pH, and nutrient content of the substrate. Much of the time, they don’t directly interact. Moss loving fungi break down dead plant material that may leach and be absorbed into the plant, but these interactions are not considered mycorrhizal. Recent studies indicate that Rickenella fibula doesn’t just coexist with the moss it is found growing with. There is actually a direct interaction going on here.”

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Colored bark mulch

We are planning to put down a seasonal mulch this spring and fall, and wondered what your opinion is of colored bark. Would brown, black, red, or some other color be best in our ornamental beds?

 

May I answer none of the above? There are better options. I can’t think of any good reason to apply mulches which have added dyes and colorants to any landscape. Check the Material Safety Data Sheets for each product to verify the source of the dye to be sure that they are not going to cause harm (to the landscape and the people and animals in it, and to stormwater). Some packaged colored mulches also have herbicides added, and I would highly recommend not using them. The sources of the “bark” may be an even more important cause for concern. This information from University of Massachusetts Extension points out that dyed bark mulch made from recycled treated wood can introduce toxic substances you would not want in your garden.

Although this is an aesthetic judgment call, to my eye, colored mulch always looks unnatural in the landscape compared to materials such as compost, leaf mulch, and arborist wood chips. Washington State University Extension professor of horticulture Linda Chalker-Scott is a strong advocate for the use of wood chips as mulch. My own observation is that bark mulch (in general, not just the colored bark products) often introduces weeds into a landscape. Chalker-Scott supports this observation in her book, The Informed Gardener (University of Washington Press, 2008):
“I have seen a number of landscaped sites where applied bark mulch immediately gave birth to horsetail seedlings.”

She further states that bark mulch from trees which have been kept in salt water can increase salt levels in your soil. Tree bark has a waxy covering, so bark mulch is not the best choice for absorbing and releasing water.

To summarize, unless you have your heart set on the look of dyed bark mulch, your garden beds would benefit from the alternative mulch materials (compost, leaf mulch, free arborist wood chips) mentioned above, plus planting an appealing and naturally colorful selection of ground cover plants in areas where that is possible.

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