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Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

Legal status of madrone in Seattle

Are madrona trees protected within the Seattle city limits?

The City of Seattle, together with Plant Amnesty, maintains a Heritage Tree Program to protect notable specimens (notable for size, form, rarity, historical import), and there is also information from the city about tree protection regulations in Seattle. Madrona, a native tree, is designated as sometimes being considered exceptional (i.e., deserving protection) Click on Tree Protection Regulations (Seattle Municipal Code, Ch.25.11) in the right hand menu. Click on Director’s Rule 6-2001 for a specific mention of madrones (Arctostaphylos menziesii: exceptional trees, p.4). Here is an excerpt:
“Healthy young specimens of Madronas on construction sites are more worth saving than old, large ones. As many specimens as possible in very good condition, regardless of size, should be preserved on construction sites, but they should not be watered or they will be more likely to decline and die. Large specimens of average or poor health may have a short lifespan because of damage during construction and as a result of post-construction practices such as irrigation are harmful to this species.”

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Dividing and transplanting iris

When is the best time to divide and transplant Irises? I have Japanese, bearded and yellow flag (I think) irises.

Rhizomatous irises (the kinds you have) are best divided in midsummer:

Lift rhizomatous kinds, such as bearded iris, in midsummer and cut rhizomes into sections, each with roots and a fan of leaves; replant, with tops barely covered, 6 inches apart. Flowers will be sparse the next year, but good thereafter.
(Source: American Horticultural Society Plant Propagation, ed. by A. Toogood, 1999, p. 202)

“The optimum time..is six weeks after flowering. This is usually in midsummer, allowing time for the new rhizome to become established and make sufficient growth to produce fans to flower the following year. New roots that began growing immediately after flowering will then be strong enough to help anchor the new plants. Early spring is another suitable time, just as the other main period of root growth is about to start, but flowering may be forfeited, and if flowers are produced the stems will almost certainly need staking. Bearded iris cultivars are tough, and if the rhizome is large they can survive out of soil for many weeks. This is not an ideal situation, but it makes transport of the plants easy.”
(Source: The Gardener’s Guide to Growing Irises, by G. Stebbings, 1997, p. 93)

Good instructions can be found in these articles:
Digging, Dividing, and Replanting Bearded Irises
Garden Experiences: Dividing Bearded Iris

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caring for Calathea

How do I care for Calathea zebrina?

The webpage of Plant of the Week have information about Calathea zebrina (zebra plant, native to Brazil):
“For the home or greenhouse. Plants reach 3 feet in containers. Leaves emerge from basal rosettes and may reach 2 feet long by 1 foot wide. Calathea zebrina need shade and temperatures above 55 degrees, but they need good light for a good, rich leaf color…use a soil mix consisting of 2 parts peat moss to 1 part loam to 2 parts sand or perlite. Good drainage is necessary or the plant will stagnate, which is a common problem. The plants should be kept moist at all times and leaves should be misted often. Fertilize every 2 weeks during the growing season and once a month during the winter months. Repot as often as necessary to avoid root bound conditions.”

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Wood boring beetle in a maple tree

I have a wood boring beetle in a maple tree and I am wondering if there is a treatment for the tree or do I need to take the tree down?

Here is a link to University of Kentucky’s entomology department website that describes a number of different species of insect borers affecting trees and shrubs, including maples.

I also consulted Pests of Landscape Trees and Shrubs: an Integrated Pest Management Guide, second edition, which suggests that prevention is best. If you can make sure the tree is protected from damage, and prune any damaged limbs and branches (should be done when adult borers are not present, Fall through February), this should help, since the borers are attracted to stressed, damaged, or diseased trees. Do not store cut wood near the tree. Insecticide is not considered effective against borers under the bark. If the tunnels are visible and there are not too many of them, you can try using a sharp wire to probe and kill the larvae, but it may be difficult to tell how far to insert the wire.

If the infestation is not severe, you may be able to save the tree by improving its care and its growing environment.

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Lemon tree, leaf loss, and scale

I have a lemon tree that is actually not dead yet, but it’s not looking good. I had to bring it in late last year as Florence [Italy] was due to have frost for a few days. Then we had horrendous winds and heavy rains. After a few weeks inside, (on a nice sunny indirect-light window sill) it started to drop everything: leaves, blossoms, tiny lemons, and now it is utterly bare. Maybe this is why? On clearing the leaves off the dirt I noticed little blister-like spots on some of the branches. I scraped them with my fingernail and they peeled off, but left sticky stuff behind. Is this a disease? Can I wash the stems? With what? I trimmed the tips of the tiny branches; they are green inside so not dead. I did fertilize with a high-nitrogen liquid, over the leaves and in the pot, a couple of times a month. I have a feeling that spider mites are doing the mischief. Is there hope?

Sorry to hear of your bare lemon tree! The loss of leaves could have been a reaction to the wind, and once the leaves are gone, the tree can become susceptible to waterlogging, pests, and diseases. It is good that you moved it inside, and that it has good light. The blister-like spots on the branches sound like a kind of scale insect, to which Meyer lemons can be prone: California red scale (Aonidiella aurantii). I do not think it would be spider mites, because they would cause stippled, yellowed leaves, and might leave telltale webs. Scale can defoliate and kill a tree. There are beneficial Aphytus wasps that can be used to control scale, but they have to released regularly to be effective and, of course, you would not do this while your tree is indoors. A good reference about scale insects and how to manage them is Pests of the Garden and Small Farm by Mary Louise Flint (University of California Division of Agriculture, 1990)

Here are two recommended books on growing citrus:

Citrus: Complete Guide to Selecting & Growing More than 100 Varieties by Lance Walheim (Ironwood Press, 1996)

Success with Citrus Fruit by Sigrid Hansen-Catania (Merehurst Ltd., London: 1998)

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Spacing for rose planting

I am using a Grandiflora rose named Prominent (Kordes) as a foreground planting; a climber (Autumn Sunset) is in the background. I love the color and the shape of Prominent’s blooms, but the blooms are sparse and plants are spindly compared to the healthy climber. Is there anything wrong with planting a new Prominent bush a few inches from each existing bush, to create fuller looking plants?

Below are some general guidelines on spacing for roses. Since you are planting a Grandiflora near a climbing rose which I am assuming has a structure to climb, you could probably get away with planting a bit closer than the 30″-36″ spacing recommended between two Grandifloras, but if you plant right up against the other rose, I imagine it would be problematic due to inadequate air circulation, which could lead to diseases. Here is what a publication of the University of Illinois Extension has to say:

“A general rule of thumb suggests that roses should be planted about 24 inches apart. This spacing will vary depending on the type of rose you are planting. Old garden roses will need wider spacing, while miniatures can be planted closer. Sufficient space between plants allows for good air circulation, an excellent first step in disease control.”

Suggested Spacing for Roses, from Jackson and Perkins:

Hybrid Teas & Grandifloras
Space: 30″ -36″ apart
Coverage: 6 -10 sq. ft.

Floribunda
Space: 24″ -30″ apart
Coverage: 4 -6 sq. ft.

English Rose
Space: 36″ apart
Coverage: 10 sq. ft.

Climber
Space: 4′ -5′ apart
Coverage: 12 -15 sq. ft.

Hedge
Space: 24″ apart
Coverage: 4 sq. ft.

Shrub
Large
Space: 30″ -36″ apart
Coverage: 6 -10 sq. ft.

Small
Space: 24″ -30″ apart
Coverage: 4 -6 sq. ft.

Miniature
Space: 12″ -18″ apart
Coverage: 1 -2 sq. ft.

Tree Rose
Standard
Space: 3′ -5′ apart
Coverage: 10 -15 sq. ft.

Patio
Space: 3′ -4′ apart
Coverage: 10 -12 sq. ft.

Miniature
Space: 2.5′ -3.5′ apart
Coverage: 6 -11 sq. ft.

Hardy plants for near the shore

Do you have some suggestions for hardy, lower growing plants that would do well near the water? Our house is on the south side of Whidbey Island. The main plantings will be behind the house, thus roughly 75-100 yards from the shore. This part of the yard has early morning sun and then some shade in the afternoon. And, since we have a large yard at home we are working toward very low maintenance at the beach.

The following plants are mentioned in April Pettinger’s book, Native Plants in the Coastal Garden (Whitecap, 2002):

SHRUBS

Arctostaphylos uva-ursi (Kinnikinnick)
Gaultheria shallon (Salal)
Vaccinium ovatum (Evergreen huckleberry)
Rosa nutkana (Nootka rose)
Holodiscus discolor (Oceanspray)
Symphoricarpos albus (Snowberry)
Mahonia aquifolium (Oregon grape)

NATIVE GRASSES

Festuca idahoensis (Idaho fescue)
Festuca idahoensis spp. roemeri (Roemer’s fescue)
Leymus mollis or Elymus mollis (Dunegrass)
Deschampsia cespitosa (Tufted hairgrass)
Festuca rubra (Red fescue)
Glyceria grandis (Reed mannagrass)
Muhlenbergia glomerata (Marsh muhly)

There are many other ideas in this book, which I highly recommend.

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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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Dwarf flowering cherry

I have an area in my garden where I would like to plant a cherry blossom (Prunus). However there are telephone and power wires above so I would like the tree to reach no more than 15 feet in maturity. Are there any dwarf or smaller growing varieties?

Here are two suggestions for smaller flowering cherry trees, from a list in Trees & Shrubs for Pacific Northwest Gardens (2nd ed.) by John A. Grant and Carol L. Grant (Timber Press, 1990):

  • Prunus serrulata ‘Shogetsu’ reaches 15 feet tall, by 22 feet wide.
  • Prunus x ‘Hally Jolivette’ reaches about 15 feet.

Here is an article by Wayne Winterrowd in Horticulture Magazine (May 1, 2007) with additional information about this tree, which he refers to as the “loveliest of trees,” and the best of the flowering cherries.

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