We have several books on dahlias in the Miller Library collection, but none provide as much photographic detail on the different forms and the methods of growing, especially the harvesting, storing, and dividing of dahlia tubers as “Floret Farm’s Discovering Dahlias.” This how-to section also has a demonstration of hybridizing and creating your own dahlia varieties.
As to be expected from Floret Farm, the use of dahlia flowers in arrangements is the heart of the book. This includes a catalog of recommended varieties, divided by color. These emphasize subtle differences. For example, pink, coral, raspberry, peach, and blush each have a separate entry.
Excerpted from the Fall 2021 issue of the Arboretum Bulletin
I need to find a photo of the eyes on a dahlia tuber.
There is good information on growing dahlias, including an image of the location of the eye on a tuber, at the website of the American Dahlia Society. To find the eye, locate the point on the shoulder, or crown, of the tuber from which the plant grows. The blog of Lynch Creek Dahlias (now archived) has good description and illustrations:
“Keep in mind that every dahlia tuber, to be viable, must have at least one eye, which you’ll see as tiny pointed protrusions on or near the neck of the tuber (the neck is the tuber’s connection to the central part of the root mass).”
The Dahlia Barn website also has images and instructions, as does the Summer Dreams Farm website.
My son and his sweetheart are planning a wedding in Seattle (my hometown) this coming September and would love to use seasonal flowers and greenery. I have not lived in the area for many years and am at a loss. Can you give us some suggestions please?
Here are some of the plants which are available in September:
Achillea (Yarrow)
Alstroemeria (Peruvian lily)
Aster
Callicarpa bodinieri (beautyberry)
Cotoneaster (for foliage)
Dahlia
Echinops
Elaeagnus (foliage)
Eryngium
Heather
Hebe (flowers and foliage)
Helichrysum (straw flower)
Lavender
Acer (Maple: foliage)
Quercus (Oak: foliage)
Skimmia
Limonium (Statice)
Viburnum tinus
Here is a link to the Washington Park Arboretum web page of seasonal
highlights.
A great book on flowers by season is A Year Full of Flowers: Fresh Ideas to Bring Flowers into Your Life Every Day by Jim McCann and Julie McCann Mulligan.
I have a line of Ward’s ruby azaleas. The three weakest ones have a lot of tiny notches in the leaves. I seem to remember the notches from the root weevil as being larger than these. Are the tiny notches from something else?
I also noticed that some of my dahlias have splotched leaves and that when I disturb the leaves, white-looking insects fly off the leaves. These flies apparently have spread to tomatoes as well. Are these whitefly? Will they disappear after the winter or is there some control I should use to prevent them from taking over?
First you need to get an accurate diagnosis of your problems. If you are in King County, you can bring samples to a Master Gardener Clinic. For information about Clinic hours see their website (Plant Clinic Schedule).
Oregon State University offers this information about root weevils and Rhododendron (which includes Azaleas). It describes using beneficial nematodes as a control.
According to Washington State University Cooperative Extension’s publication, How to Identify Rhododendron and Azalea Problems (1984), root weevil damage to foliage is not usually a serious problem. You can check for weevils with a flashlight at night to confirm that they are the source of the notches you are seeing. There are some Neem oil-based products that may be helpful, but they must be used at the correct times of year. See WSU’s HortSense page.
As for the dahlias and tomatoes, it is important to determine exactly what the insects are before proceeding with treatment. If they are whiteflies, you can put yellow sticky traps around the plants to trap them. University of California, Davis’s Integrated Pest Management site has other recommended control methods, including reflective mulch. You may not want to use insecticidal soap:
“Insecticides have only a limited effect on whiteflies. Most kill only those whiteflies that come in direct contact with them. For particularly troublesome situations, try insecticidal soap or an insecticidal oil such as neem oil or narrow-range oil. Because these products only kill whitefly nymphs that are directly sprayed, plants must be thoroughly covered with the spray solution. Be sure to cover undersides of all infested leaves; usually these are the lowest leaves and the most difficult to reach. Use soaps when plants are not drought-stressed and when temperatures are under 80 degrees F to prevent possible damage to plants. Avoid using other pesticides to control whiteflies; not only do most of them kill natural enemies, whiteflies quickly build up resistance to them, and most are not very effective in garden situations.”
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.”
I have some beautiful red dahlias in two flower boxes on my front
porch. Two questions: I noticed some of the leaves at the bottom
of the plants are turning yellow and dropping although the plants
are still blossoming. What to do? Also, do I need to remove them
from the soil for the winter here?
To answer your second question first, you don’t have to dig up your
dahlias unless you prefer to do so. Here is what local gardening expert
Marianne Binetti says on this subject in her Seattle P-I
column:
“Laid-back gardeners should just leave their dahlia tubers in the ground.
Cut back the top growth after the first hard frost and then cover the
dahlia bed with a waterproof oilcloth tablecloth or tarp. Secure with
rocks or bark mulch. This keeps the tubers dry and in the spring you can
remove the covering and see what comes up. For dahlias worked into a
mixed bed, you can pile sword fern leaves on top and weigh these down
with a rock.
“It is the wet more than the cold that kills dahlia tubers.
“If you really need to dig and store dahlias, place them in open paper
bags, never plastic, and let them dry in a covered area for a few days
before storing.”
As for the yellowed leaves, it is hard to diagnose the problem via
e-mail. There is a chance that you could safely just keep removing and
disposing of the yellowed leaves. However, there are problems like
leafhoppers (an insect which feeds on the leaves and causes them to
become speckled, then turn dry and drop off), or viral diseases which can
cause yellow spotting or mottling of the leaves. I looked at The
Gardener’s Guide to Growing Dahlias by Gareth Rowlands (Timber Press,
1999), and found descriptions of leaves which have turned yellow due to a
number of causes, including chlorosis (the leaves are unable to produce
enough chlorophyll, and turn yellow if there us still carotin present, or
white in only xanthophyll remains). When a mature dahlia turns yellow, it
may be due to a nutrient imbalance (such as lack of magnesium or iron).
Without having the plants diagnosed, it is impossible to recommend a
remedy, so you may want to bring samples to a Master Gardener Clinic.
Should you dig your dahlias or not? Enthusiasts dig them up every autumn when the clocks get turned back. They dust the tubers with fungicide, divide them up and finally store them in a cool place in slightly damp vermiculite. For those of us not so dedicated to our dahlias we can leave them in the ground provided that the soil is well drained and doesn’t freeze. A little patch of plastic can help keep the spot dry over winter. For more dahlia growing tips go to the Puget Sound Dahlia Association website
The Seattle Dahlia Society is a non-profit organization created for Northwest Dahlia enthusiasts. We grow, promote and show Dahlias in the Pacific Northwest. Members meet each month on the second Wednesday with the exception of July and December, at the Shoreline Senior Center at 7:30 pm. The Seattle Dahlia Society holds an annual tuber and plant sale each April that is not only open to members, but to the general public as well. Each year on Labor Day weekend, the Seattle Dahlia Society puts together a show so that growers can share their hard efforts with fellow club members as well as the public; the event is free. Membership information is available on the website, as well as information about dahlias and the club.