controlling powdery mildew

What can I do about powdery mildew on my dahlias? Should I throw the bulbs away, or does it only contaminate the plant above the ground? I have heard both too much water and not enough water cause this problem. Is either true?

The main thing you will need to do is destroy all the foliage affected by the mildew. The mildew can survive the winter on infected foliage, and then spread to new foliage.

Powdery mildew thrives where plants are crowded and there isn’t enough air circulation, so give your plants space, a sunny site, and try watering in the morning, and watering from beneath the plants (not over the leaves) so they are able to dry off during the course of the day. As you indicated, too little water can also be a problem.

Here are two websites with additional information:
Univ. of California IPM Online Guide
Washington State University Extension

I did not come across any information specifically saying that powdery mildew will affect bulbs or tubers. I spoke to an experienced dahlia and begonia grower here who said that it should be all right to store and replant your tubers, as long as you thoroughly get rid of all the diseased foliage aboveground.

Some sources (such as The Organic Gardener’s Handbook of Natural Insect and Disease Control, edited by Barbara Ellis, Rodale Press, 1996) suggest that a baking soda spray (1 tsp. per 1 quart of warm water, with a bit of dish soap) is protective or preventive, but Washington State University Extension professor Linda Chalker Scott disputes the efficacy of this method. She says that other methods work better:
“Other treatments have been more successful in powdery mildew control, including horticultural oils, potassium bicarbonate, potassium phosphate, sulfur, milk, and even water sprays. Probably the most field success has been found in combining SBC [sodium bicarbonate] with horticultural oils, including mineral and vegetable oils (see the Fall 2008 MasterGardener magazine). The mixtures are so effective that they’ve been successful even on serious powdery mildew epidemics.”

care and maintenance for Phormium

What is the maintenance routine for Phormium?

According to Sunset Western Garden Book (2007), Phormium require well-drained soil, and may be prone to crown rot if the site is poorly drained. They are susceptible to damage from cold (below 20 degrees Fahrenheit). The Plant Care Manual by Stefan Buczacki (Crown, 1993) suggests that you provide them with full sun and shelter from cold winds, especially if your plants are variegated cultivars, which are less hardy. Mulch in spring and fall, and provide a balanced fertilizer mid-spring and midsummer. In fall, wear heavy gloves and cut or pull away dead foliage. You may need to divide every 5-6 years.

controlling dandelions without pesticides

I have a smaller lawn, in a slightly shady area and have been having problems with dandelion and white clover. I don’t mind a few weeds, but it is getting to be too many. Children and pets play on this lawn so I don’t want to put anything that would be toxic to them on the lawn. What would you suggest I do?

Given that you are concerned for your children and pets, it makes sense to hand-weed your lawn. A little pocket knife is a great tool for doing this quickly and tidily. If you just spend a little bit of time at it a few days a week, it will go faster than you might imagine. Try to live with the clover; it is extremely difficult to eradicate, and it is great for honeybees.

Small dandelions are easier to pull out. The City of Seattle has excellent information about caring for lawns without pesticides, including hints about controlling dandelions. Look in the right-hand menu for additional links to lawn care information.

This article on Dealing with Dandelions from the Journal of Pesticide Reform (Fall 2001) describes several types of dandelion weeding tools.

insect pests in the garden

Is it normal to have many different insect pests in one garden? Is it a sign that I am not taking care of my plants well? Everything looks fine except for one infestation after another!

As far as I am concerned it is perfectly normal to have all of these pests (because I also have many)! But some gardeners are more ruthless than I am. They would rip out the plants. Others would assault their garden with chemicals. I prefer the middle ground of tolerance of some damage and using low-toxic controls.

The mantra these days is RIGHT PLANT RIGHT PLACE and HEALTHY SOIL = HEALTHY PLANTS. For further information (and support) go to the Seattle Public Utilities website, which has a number of great publications on Natural Lawn and Garden Care.
There are lots of links to browse.

There is also information about Natural Pest, Weed, and Disease Control.

Other good resources are Toxic-Free Future (formerly known as Washington Toxics Coalition) and Northwest Center for Alternatives to Pesticides.

using treated wood and other alternatives

We are thinking about putting in a retaining wall and a fence on our property, which is near a lake. Should we avoid using pressure treated wood? If so, what are some alternatives?

There are many reasons not to use treated wood for your fences and/or retaining walls. The chemicals most used to preserve wood—creosote (on railroad ties, among other things) and penta—were banned by the EPA in 1986 for indoor use and for many outdoor uses. The chemical used to pre-treat wood (CCA, a mixture of copper, chromium, and arsenic called chromated copper arsenate) has been shown to leach into the soil and to transfer to human skin through contact.

There are safe paints and preservatives for coating wood; there are safe types of pre-treated wood; some people use stone, cement blocks, or other materials instead of wood.

Below is lots of info about treated wood and alternatives.

Start with the page on the EPA site, which is full of information on treated wood. It includes a section on alternatives and some questions and answers about studies.

If you find this too technical, try the next two links below.
The Natural Handyman website has good information.

Toxic-Free Future (formerly known as Washington Toxics Coalition) has a fact sheet about safe and unsafe paints and wood preservatives. Lots of background information on the toxicity of treated wood is included as well.

khat tree intoxication

Recently I met an Ethiopian couple who were picking the reddened leaves on an otherwise green bush/tree in my front yard. The man explained this was a “cat” or “chat” tree, the leaves produce a drugged like state when ingested. He asked me if he could harvest the tree, and asked me not to tell any other Somalis, Ethiopians, or Eritreans in the neighborhood about my tree. He also told me that if I lived in Mogadishu, this tree would make me a wealthy man! He ate some leaves in front of me, and I tried a couple, but they were bitter and unpalatable to my palate. I experienced a feeling of empowerment, strength, and mental alertness. Obviously the “Chat Tree” has some relationship to the “Bongo” young Somalis chew.

During the worst of the anarchy in the late 1990s in Mogadishu there was a lot of news footage of the street gangs, high on the plant they were chewing, and armed with machine guns and machetes, creating havoc.

Do you know the history of this tree?

What are the properties that cause the intoxication?

What is the tree’s botanical name?

Should I report the tree’s existence to the authorities?

Can you tell me what I have here?

p.s.-These trees are common front garden bushes that were widely planted in Perth, Western Australia. Next time I see someone hanging out under one of them, I think I will know why!

The chat, or khat tree, is Catha edulis (Celastrus edulis), and the leaves and branchlets have properties that stimulate the central nervous system. In addition to the euphoric or inebriating properties, chewing the leaves can cause irritability, decreased appetite, gastric upset, constipation, and inflammation of the mouth. Habitual use can lead to periodontal disease, and increased risk of esophageal cancer. The active compounds are Alkaloid D-norpseudoephedrine, as well as other alkaloids, and tannins. (Source: Medical Botany: Plants Affecting Human Health by Walter H. Lewis; John Wiley & Sons, 2003, 2nd ed.)

The Handbook of Medicinal Herbs by James A. Duke (CRC Press, 2002, 2nd ed.) indicates that Catha edulis has been used medicinally to treat a great number of ailments, including asthma, depression, diarrhea, glaucoma, and low blood pressure. Use of khat is an ancient, socially acceptable tradition in the Afro-Arabian culture (and became known as a recreational drug in the USA after American soldiers were exposed to its use in Somalia. Khat is subject to legal restrictions in many countries. (Medicinal Plants of the World by Ben-Erik van Wyk; Timber Press, 2004).

As for whether to report the harvesting of leaves from your tree, that would depend on whether khat use is specifically prohibited by law in Australia.

mulching Pacific Northwest native plants

Is is good to mulch Arctostaphylos uva-ursi? If so, would an aged bark be best or a mulch that contains manure? How deep should the mulch be?

Native Plants in the Coastal Garden (by April Pettinger, 2002, p. 27), says the following about mulching Pacific Northwest native plants:
“…When an established native plant garden requires maintenance, it is usually minimal: mulching is probably the most important—and often the only—maintenance required. In any garden, mulching is arguably the most beneficial care you can give your soil and your plants. There are many advantages to using mulch. It suppresses weeds, conserves moisture by minimizing evaporation, and releases nutrients to the soil…Good mulch materials are compost, decaying leaves, well-rotted manures, sea kelp, mushroom compost, seedless hay or straw, shredded prunings, natural wood chips, grass clippings and evergreen needles and cones. Commercially available screened bark—usually referred to as bark mulch—has little to offer other than its ability to conserve water; it has no nutritional value and in fact depletes the nitrogen in the soil. When spreading mulch, don’t pile it too close to stems of plants. If you are using compost as mulch, spread it about 2 to 4 inches deep. Other materials may be applied to a depth of 3 to 7 inches…”

butterfly conservation in the Pacific Northwest

I have become interested in helping with the conservation of monarch butterflies, whose caterpillars feed only on milkweed. We are supposed to plant milkweed. I am also gradually converting my small Seattle garden to a native-plant garden. Do these two goals contradict each other? Are any of the milkweeds native to Seattle and vicinity? Would monarchs themselves be an exotic species here?

It’s wonderful that you want to help with butterfly conservation. Monarch butterflies are not frequently seen in the Puget Sound region and, as you may be aware, it is too cold for them to overwinter here (they need an air temperature of at least 50 degrees Fahrenheit, according to Jerry Sedenko’s The Butterfly Garden [Villard Books, 1991]). However, you can do several things to make your home landscape hospitable to the pollinators we do have in our area, including not using any pesticides in your garden and persuading your friends and neighbors to refrain from using them also.

The Monarch Joint Venture project links to the Xerces Society’s Milkweeds: A Conservation Practitioner’s Guide which has information on milkweed species and their natural habitats. The plants recommended by the MJV for the West are Asclepias speciosa and Asclepias fascicularis but these plants may not be successful in the Puget Sound region. Both species are found mostly east of the Cascades as these maps from the USDA show. (click on the detail maps for Washington State)

The Xerces Society for Invertebrate Conservation has useful information(now archived) about Western Monarchs, as well as separate pollinator conservation resources (for different types of pollinators–not Monarchs) for the Pacific Northwest.

You might be most effective in supporting the Monarch conservation effort financially but devoting your gardening efforts to conservation of species that are native to our area. Here are the Xerces Society’s list of Pacific Northwest butterflies and bees.

The Puget Sound Beekeepers Association has information on bee-friendly gardening.

The issue of using native plants in our urban gardens is a complex one. How do we define the native status of a plant? Sometimes the only plants available in nurseries are cultivated varieties of native species: are they still ‘native?’ Are plants that have naturalized in our area native? Do we have the ideal conditions in our garden to sustain native plants?

My personal outlook on this is that it’s best not to think too rigidly about what is native and what is not, but instead to be vigilant about what is overly aggressive or definitively noxious and invasive, and to try to grow a diverse range of plants that will thrive without excessive watering, fertilizing, and fuss, and select plants (native and otherwise) will attract birds, beneficial insects, and local species of butterfly. Here is Washington State University Extension horticulturist Linda Chalker-Scott’s essay on the topic of native plants.

fasciation or crested growth in plants

The ends of some of my Daphne odora branches look like several branches fused together. What causes this, and is there something I should do?

What you are describing sounds like fasciation, which is a kind of genetic mutation. Professor T. Ombrello of the department of biology at Union County College describes this condition:
Excerpt:
“One interesting type of mistake that is occasionally found in plants is known as a fasciated or crested growth form. It is usually the result of a growing point changing from a round dome of cells into a crescent shape. Subsequent growth produces a flat stem. In some cases fasciation is the result of several embryonic growing points fusing together, with the same flat-stem appearance. [… ] What causes plants to produce fasciated stems? For the most part, we just don’t know. Fasciation has been induced experimentally by applications of plant hormones, severe pruning, wounding, and atypical day lengths. Most, however, appear by chance with no obvious cause.”

University of Arkansas Extension addresses the phenomenon of fasciation.

Possible causes for this condition:

bacterial infection
inherited genetic trait
herbicide, insect, or physical damage to the growing tip
garden conditions that favor rapid growth
spontaneous mutations

There are good illustrations and explanations on the blog of Tentative
Plant Scientist, as well.

You don’t need to do anything, unless you would like to remove the odd-looking growth. You may want to look into whether herbicide has been used, or if there have been insects feeding on your Daphne. Also, avoid over-fertilizing, which could promote excessively fast growth.

variation of color in Hydrangeas

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).