Growing Dahlias

How to Plant	Topping or Pinching and Disbudding	Cut Flowers	Winter Storage
Watering and Fertilizing	Pests and Disease	Digging	Dividing

Dahlias are considered one of the most spectacular garden flowers. They are also thought to
require a great deal of care. Both of these statements are true to some extent. There is a great
variety of form in dahlias, from the showy dinner-plate size to the bright, little single ones. Wait
until all danger of spring frost is past before planting (from mid April through May, in most areas)

How to Plant
The ground should be warm and well drained. The soil should be rich with a pH of about 6.5 – 7.0.
If the soil is clayey, add sand or peat moss. Compost of any type should be avoided. Put a small
handful of bone meal in the planting hole and work in well before planting the tuber.

Dahlias should be planted in a sunny location. Place the tubers horizontally 4-6 inches deep and
about 18” to 24” apart. Water after the first sprouts appear. Since all dahlias that will be three
feet or taller require staking, it is a good idea to place the stake (bamboo stakes or metal rods)
when planting the tuber to avoid damaging the tuber by guessing its position later.

Growing dahlias in containers is not recommended, but if you choose to, low growing or dwarf
dahlias work best. A container should be no smaller than 12”x12” per tuber. Use two parts garden
soil with one part potting soil. Water sparingly until after plants are 12” high, then extra watering
and fertilizing are needed to promote proper blooming.

Watering and Fertilizing
After dahlias are established, water deeply 2–3 times a week – more during warm, dry weather.
Proper watering promotes proper blooming. Hand watering is not enough. Avoid wetting the foliage.

Dahlias require fertilizer that has low nitrogen and high percentages of phosphorus and potassium,
such as 5-10-10, 10-20-20, or 0-20-20. The first application should be within 30 days of planting
and then repeat approximately 3-4 weeks later. DO NOT OVERFEED. Avoid compost, fish fertilizers,
and high-nitrogen, water soluble types as they promote weak stems, small or no blooms, and tubers that rot or shrivel while in storage. Do not fertilize after mid-August.

Topping or Pinching and Disbudding
To promote shorter, bushier plants, pinch or cut the terminal bud just above the third pair of leaves
(or plant height of about 18-20” tall). This will produce two main stems.

When flower buds are visible, begin disbudding as this will increase the bloom size. Flower buds
come in three's: the central leader bud will produce the largest bloom. Remove the smaller flower
buds on each side of the leader bud by pinching or cutting to the base of the leaf axil. Further
down the same stem, two more buds will be found in the leaf axils and these, too, should be
removed.

Pests and Disease
Major pests of dahlias include aphids and slugs early in the growing season, and mites in mid- to
late-summer. Thrips, earwigs, caterpillars, and wasps may occasionally attack dahlias. Leafspot,
mildew, and dahlia wilt also can be problematic. Consult your county Extension agent for
recommended controls.

Cut Flowers
Flowers should be cut when fully opened. Cool, early morning cutting will provide the longest lasting
cut flowers. As soon as you cut the bloom, plunge the stem into two to three inches of very hot
water (approximately 160-180 degrees). This will set the blooms and the flowers will last for four to
six days. Remove old blooms to keep the plants strong and blooming until frost.
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Digging
Lift tubers out of the soil about 2 weeks after a killing frost – the plants will turn brown if frosted
hard enough. Tubers dug too early are still “green” and will not store. It is safe to dig by mid
November without a total frost. Because tubers may have spread quite a distance, begin digging
far enough from the plant so as not to damage them. A spading fork or spade works well for this
task.

Once the tubers are out of the soil, remove as much soil as possible without damaging the tubers.
Soil may also be washed from the tubers with water under pressure. Cut the stalk off to about six inches; turn the tubers upside down to drain the stem and allow the soil to dry. When dry, remove
the remainder of the soil. Cut off any small roots. Remove and discard tubers that are damaged or diseased, and dust any cut surfaces with sulfur. Allow the tubers to air dry, protected from the elements for about 24 hours.

Winter Storage
Tubers should be stored in crates or cardboard boxes. Line the containers with ten to twelve
sheets of newspaper and, starting with the storage medium (slightly dampened peat moss, sand,
or sawdust/shavings) in the bottom, layer tubers and medium until the container is full. Never store
in sealed plastic bags or plastic containers. Store in a cool, dry place with temperatures of 40-50 degrees F. Too warm and tubers will shrivel; too cold and they will freeze or rot. Check tubers
once
a month throughout the winter.

Dividing
Bring the tubers out of storage in March or April and locate eyes on each tuber. With a sharp knife, divide the tubers with a portion of crown attached, so that each piece has an eye. If eyes are not evident, place the tubers in moist leaf mold, peat, or soilless mix. In a week or two the eyes will
appear. Pot the divisions in a sterilized, soilless mix or porous potting soil with the crown above the potting medium. Provide the potted divisions with maximum sunlight and a temperature of about 55 degrees F. Water when the potting mix dries to a depth of one inch. Good ventilation will help
prevent disease.

 Source: Swan Island Dahlias; Ohio State University Extension Fact Sheet.

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