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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

Plant division and propagation

I am wondering if the following plants can be divided or propagated successfully: Heuchera, Donkey Tail Spurge (Euphorbia), Corsican Hellebore, and Helianthemum.

I consulted The American Horticultural Society Plant Propagation book,
edited by Alan Toogood (DK Publishing, 1999), and it says the following:

  1. Heuchera: by division or by seed in spring. Since cultivars may not
    come true from seed, I would recommend dividing your plants. Once spring
    growth has begun, lift the plant from the ground and remove small
    sections from around the edge (look for good roots, and 2-3 shoots).
  2. Euphorbia myrsinites: (Just a note: based on the USDA information that
    this plant is invasive in Oregon and banned in Colorado, I would think twice before propagating it. This species does a fine job of propagating itself, apparently. In general, the genus Euphorbia can be propagated by division in early
    spring, or from spring to summer, by seeds in fall or spring, and by cuttings in summer or fall, but if you were to propagate by cuttings, you would need to protect your skin from the sap.
  3. Helleborus argutifolius can be propagated by division after flowering,
    or by seeds in summer. Test seed capsules for readiness by gently
    squeezing. If the seed capsule splits to reveal dark seeds, it is ready
    for harvest. Wear gloves! H. argutifolius (Corsican hellebore) often
    self-seeds. Check around the base of the plant in spring. When each
    seedling has at least one true leaf, gently lift and transplant to moist,
    fertile soil in light shade.
  4. Helianthemum can be started from greenwood cuttings rooted in summer
    and fall, and by seeds sown in spring in a frost-free location.

If you would like further information on the relative ease or difficulty
of each of these methods for each of these plants, I recommend coming to
the Miller Library and looking at our books and other resources on
propagation. Here is a link to a booklist.

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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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Houseplants and indoor air quality

I would like to grow plants in my dorm room to improve the air quality. Which plants are most effective?

There was a NASA study on houseplants and indoor air quality in 1989. The study has to some extent been disputed and/or discredited. A January 17, 2018 article in Time magazine discusses it. Here is an excerpt:

“‘There are no definitive studies to show that having indoor plants can significantly increase the air quality in the home to improve health in a measurable way,’ says Luz Claudio, a professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai.

“Claudio has reviewed the research on the air-quality benefits of indoor plants. She says there’s no question that plants are capable of removing volatile chemical toxins from the air ‘under laboratory conditions.’ But in the real world—in your home, say, or in your office space—the notion that incorporating a few plants can purify your air doesn’t have much hard science to back it up.

“Most research efforts to date—including the NASA study—placed indoor plants in small, sealed environments in order to assess how much air-scrubbing power they possessed. But those studies aren’t really applicable to what happens in a house, says Stanley Kays, a professor emeritus of horticulture at the University of Georgia.”

A 2019 study by Bryan Cummings and Michael Waring, published in the Journal of Exposure Science and Environmental Epidemiology concludes that “potted plants do not improve indoor air quality.” The study is summarized in this article from Science Alert.

The Environmental Protection Agency has useful guides to maintaining good indoor air quality, one aimed at health care professionals, and one for the general public.

Here are excerpts from each:

“Recent reports in the media and promotions by the decorative houseplant industry characterize plants as ‘nature’s clean air machine’, claiming that National Aeronautics and Space Administration (NASA) research shows plants remove indoor air pollutants. While it is true that plants remove carbon dioxide from the air, and the ability of plants to remove certain other pollutants from water is the basis for some pollution control methods, the ability of plants to control indoor air pollution is less well established. Most research to date used small chambers without any air exchange which makes extrapolation to real world environments extremely uncertain. The only available study of the use of plants to control indoor air pollutants in an actual building could not determine any benefit from the use of plants. As a practical means of pollution control, the plant removal mechanisms appear to be inconsequential compared to common ventilation and air exchange rates. In other words, the ability of plants to actually improve indoor air quality is limited in comparison with provision of adequate ventilation.”

“Over the past few years, there has been some publicity suggesting that houseplants have been shown to reduce levels of some chemicals in laboratory experiments. There is currently no evidence, however, that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices. Indoor houseplants should not be over-watered because overly damp soil may promote the growth of microorganisms which can affect allergic individuals.”

All that being said, houseplants can, at the very least, provide an aesthetic improvement to a room, and as long as you are careful not to overwater, they shouldn’t hurt air quality.

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Brugmansia and the “Devil’s Breath”

I know that Brugmansia has toxic and intoxicating properties. I heard a story about a railway carriage in Europe that was filled with the Brugmansia flowers. When the doors to the carriage were closed, the fragrance of the blooms caused the passengers to lose consciousness, and their valuables were stolen. Plausible, or urban legend?

Brugmansia, like the related solanaceous plant Datura, contains tropane alkaloids throughout the plant, including the seeds and flowers. One of these alkaloids is scopolamine. There are many tales of “Devil’s Breath,” a processed form of scopolamine (as powder), or scopolamine-rich seeds being used by criminals in various parts of the world to drug their victims into unconsciousness. There is an article in The Guardian (September 2, 2015) which suggests it’s unlikely that this substance would have been used to “zombify” travelers in Europe. There are, however, travel security warnings from the U.S. State Department about its use by criminals in Ecuador and Colombia.

A scientific article, “Volatile compounds emitted from flowers and leaves of Brugmansia X candida (Solanaceae)” (G.C. Kite and C. Leon, in Phytochemistry, 1995) states that volatile tropane alkaloids could not be detected in the fragrance of either flowers or leaves; the main volatile organic compounds emitted by the flowers are terpenoids, benzenoids, and indole. Those compounds can cause headaches but it seems unlikely they would act like a sedative.

The book Plant Intoxicants by Baron Ernst von Bibra (Healing Arts Press,1995) describes use of Datura seeds by criminals in India to knock out their victims. There are many traditional medicinal uses of Brugmansia among the indigenous tribes of Colombia, but the hallucinogenic effects are especially frightening. One tribe describes the pleasant scent of the flowers but warns that the plant is inhabited by an evil spirit and all who sit at the foot of the tree “will forget everything.” (Source: Plants of the Gods, Richard Evans Schultes, Healing Arts Press, 2001). However I cannot find any confirmation for your colorful story of a train carriage full of drugged passengers among the Brugmansia flowers.

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Callicarpa varieties and planting time

I have a Callicarpa with light green leaves and very small purple berries in the winter. I don’t know what the one I have is called, but I would like to find one with dark green leaves and dark purple berries. How late in the season could I put a shrub like this in my yard in South Seattle?

Sometimes having two Callicarpa plants in one garden will enhance berry production. The variety that reportedly does best in the Pacific Northwest is Callicarpa bodinieri var. giraldii ‘Profusion.’

I wonder if the variety you currently have might be this one, Callicarpa dichotoma ‘Early Amethyst,’ which has paler purple berries that are fairly small.

I’d never heard of the cultivar ‘Pearl Glam’ before, but it appears to have darker (purple-tinged!) leaves and richly purple-colored fruit.

Portland-area gardener and author Ketzel Levine writes about several types of Callicarpa in Plant This! (Sasquatch Books, 2000). She says that Callicarpa bodinieri var. giraldii ‘Profusion’ is the only type of Callicarpa “that truly thrives in temperate climates” (such as ours). “For reasons […] no doubt related to the weather, and the absence of a long season of heat—none of the other species berry up quite as reliably.” She does say that Callicarpa americana‘s berries are three times larger than ‘Profusion’ and that Callicarpa dichotoma is a more graceful plant (“the most refined and shapeliest species in the genus. It has a horizontal, tiered habit,” but its berries are smaller. Callicarpa japonica has “metallic purple fruits, a color just a tad weirder than most, set off dramatically by autumn leaves often touched with pink.” There is a white-berried form of Callicarpa japonica–‘Leucocarpa.’

However, all of the other varieties (aside from ‘Profusion’) may not perform well in the Pacific Northwest.

You can plant more Callicarpa plants as you find them in nurseries or at plant sales. To be on the safe side, don’t plant in summer heat or you will have to pay very close attention to watering, and don’t plant when the ground is frozen or saturated. Spring or fall planting will work just fine.

On sex difference among eggplant fruits

I read on a cooking blog that it’s important to be able to distinguish between male and female eggplants, because males are less seedy and therefore less bitter. Supposedly, the difference can be detected by looking at the indentation at the bottom of the vegetable. Females have long, deep, dash-shaped dents, and males have round, shallow ones. This is the first time I’ve ever heard of such a thing, and I’m wondering if you can confirm it.

There is no sex difference among eggplant fruits. The confusion may have come from the fact that eggplant flowers have male and female parts. Mary Keith, a nutrition educator with University of Florida Extension says:

“Please, don’t waste any sleep over trying to remember which one is which.
There are not ‘male’ or ‘female’ eggplants. They all come from the female organs of the
flower, but eggplant flowers have both male and female organs. The seeds they
contain will grow into plants that make flowers with both male and female parts.[…] The shape of the scar where the flower fell off doesn’t tell you whether the fruit is a boy or a girl.”

Keith goes on to explain the best way to select an eggplant for cooking purposes:

“The best place to start is what you can see, the skin. There should be a little bit
of the stem still attached to one end. A ripe eggplant will have a smooth, bright, shiny
skin. It should be firm, not hard but not soft and soggy either. Whether it is purple, green, white or striped, if the skin is dull the fruit has been picked for too long. When you press on the skin it should spring right back at you. If it’s too hard to press in, then the fruit is too green and underripe. If it goes in and stays in, the fruit is too old. The texture is getting soft and it is more likely to be bitter. In general the smaller ones are usually better. Probably the best way to decide which ones to buy is to weigh them. […] The heavier one will be the better one. Some people say they can tell by knocking on an eggplant as they do a watermelon. In this case though, you do not want to buy one that sounds hollow. These will be dry and punky inside.”

Similar information comes from University of Illinois Extension:

“There is long-standing controversy about male and female eggplants, which is an inaccurate approach considering the fact that fruits are the product of sex and do not have it. However, it is folk wisdom worth some attention. Eggplants have a dimple at the blossom end. The dimple can be very round or oval in shape. The round ones seem to have more seeds and tend to be less meaty, so select the oval dimpled eggplant.”

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Growing peppers in the Northwest

For the past several years, I have tried to grow green peppers in our garden. The problem I have had is that they never grow very big, and the peppers never get much bigger than a small plum. I fertilize my garden, add compost, but still get small peppers.

Peppers are tricky in our climate. Quoting from Growing Vegetables West of the Cascades by Steve Solomon: These heat-loving plants do not readily adapt to climatic conditions north of the Yoncalla Valley..they are often irreversibly shocked by outdoor night-time temperatures below 55 F.Many gardeners make the mistake of setting peppers out at the same time as tomatoes right after there is no frost danger. This, however, will almost certainly expose them to overnight temperatures of 45 F or even worse. Any surprisingly cool night during June can shock peppers sufficiently to stop their growth for a time.
North of Longview, Washington, and along the coast, only the hardiest pepper varieties will grow in cloches or greenhouses.

Source: Growing Vegetables West of the Cascades, by S. Solomon, 2000, p. 210, 236.

Oregon State University has an article entitled “Spice Up Your Garden with the Perfect Pepper” with a link to a guide to growing peppers in the Northwest.

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Lilac blooming habits

I have a lilac shrub that is about six or seven years old and blooms every other year. This seems very odd to me. Most lilacs bloom every year. Is blooming every other year normal? It is planted in optimal conditions and looks very healthy.

Quoted directly from Lilacs for the Garden, by J. Bennett (2002, p. 99): “Some lilacs, especially cultivars of the common lilac (Syringa vulgaris) bloom better, or only, in alternate years. Pruning the plant soon after it does bloom may encourage flowers the next year.”
University of Nebraska Extension says that “removing the seed capsules soon after flowering has been reported to alter the every-other-year flowering cycle in some lilacs. This is because less energy goes into the current year’s seed production and more into the next year’s flower production. Some researchers agree with this recommendation and some do not. Removing seed capsules also improves the plant’s appearance.”

I could not find a list of which cultivars do this. You might consult the International Lilac Society to see if a list exists.

Another resource is the Hulda Klager Lilac Gardens (in Woodland, WA about 30 minutes north of Portland).

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Narrow or fastigiate trees

Can you recommend some narrow or fastigiate trees for the space between our house and the house next door? The space is about 14 feet wide. Will Cornus kousa ‘National’ work?

From what the experts say, Cornus kousa grows 20-30 feet high and wide in cultivation. They can grow to twice that size in the wild.

I found this and other information that might help you in the sources below:
1. Trees and Shrubs for Pacific Northwest Gardens, by J. Grant, 1990, p. 71
2. Trees & Shrubs Hardy in the British Isles, by W.J. Bean, 1976, p. 703
3. Manual of Woody Landscape Plants, by M. Dirr, 1998, p. 260
4. North American Landscape Trees, by A. Lee Jacobson, 1996, pp. xiii, 144

The Seattle City Arborist’s Office recommends the following narrow trees:
1. Magnolia grandiflora ‘Little Gem’ – 15 ft. high, 10 ft. wide. White flowers, evergreen.
2. Malus ‘Adirondack’ – 18 ft. high, 10 ft. wide. White flowers, red fruit, excellent scab resistance.
3. Malus ‘Red Barron’ – 18 ft. high, 8 ft. wide. Red flowers, red fruit, yellow fall color.
4. Malus ‘Golden Raindrops’ – 18 ft. high, 13 ft. wide. White flowers, yellow fall color, abundant yellow fruit.
5. Prunus serrulata ‘Amanogawa’ – 20 ft. tall, 6 ft. wide. Pale pink double flowers, bronze fall color.

Here are additional sources:

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Pinching rhododendron buds

A friend was told that pinching out growth buds before they begin to elongate as a means of shaping young rhododendrons would only stimulate buds further down the stems that were less than 4 years old – older than that and the growth buds would no longer be viable. I cannot find any information to suggest 4 years viability of dormant buds to be true, or untrue. Can you help?

Though pinching encourages multiple branching lower down the stem, I find no reference to it being done at a particular age.

“This practice (pinching) is recommended for most larger rhododendrons until they reach flowering size…”
(Source: A Plantsman’s Guide to Rhododendrons, by K. Cox, 1989, p. 101)

That statement indicates a younger plant, but the author then mentions several exceptions.

Here is some how-to information about pruning online:

7 Solutions to the Too-Big Rhododendron.

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