are considered one of the most spectacular garden flowers, but they
are often thought of as plants requiring a great deal of care. Although
this is true to some extent, as dahlias do require some special
care, especially lifting for winter storage, beautiful dahlia blooms
can thrive in the garden from July until frost with minimal care.
There is a great variety of form in dahlias, from showy dinner-plate
size to the small, bright single dahlias.
should be planted in a sunny location. The soil should be rich and
well drained with a pH of about 6.5. Wait until all danger of spring
frost is past before planting.
dahlias can be planted 9 to 12 inches apart. The smaller-flowered
types, usually about three feet tall, should be spaced two feet
apart. The taller, larger-flowered dahlias should be spaced three
feet apart. Dig the planting hole slightly larger than the root
ball of the plant and incorporate some compost or sphagnum peat
moss into the soil. Plant dahlias so the crowns are just above soil
level. Tall, large-flowered cultivars will require support. Place
stakes (five to six feet tall) around plants at planting time and
tie stems to them as the plants grow.
around dahlia plants carefully, as they tend to have shallow roots.
Mulch plants with well-aged compost, aged manure, peat or straw
at the end of June. Water plants regularly if rain is insufficient,
but avoid wetting the foliage. Dahlias require a rich soil; a commercial
fertilizer low in nitrogen (such as a 5-20-20), worked into the
soil a month before planting, is good preparation. As plants grow,
a monthly feeding will encourage large blooms. If using a granular
fertilizer, water-in thoroughly after application. Do not fertilize
dahlias after mid-August.
the plants reach a height of three to four inches, pinch the terminal
bud just above the second pair of leaves. This will produce two
main stems. When flower buds are visible, begin disbudding. This
will increase the bloom size of the leader bud and improve the flower
stem formation. Flower buds come in sets of three. The central leader
bud will produce the largest bloom. There will be a smaller flower
bud on each side of the leader bud. Remove these side buds 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 which should also
should be cut when fully opened. Early morning cutting will provide
the longest lasting cut flowers.
Major pests of dahlias include aphids
and slugs early in the growing season,
and mites in mid- to late-summer. Thrips, earwigs
and wasps may occasionally attack dahlias. Leafspot and dahlia wilt
also can be problematic. If the leaves yellow in a random pattern,
submit a sample for diagnosis. A plant with a viral infection should
be removed from the garden immediately. Destroy plants with abnormal
or deformed crowns.
Lift dahlias after the first frost or before the end of October.
Before lifting tubers, remove all ties. Stakes should be cleaned,
repaired and stored. Attach name labels to the base of the main
stem of named cultivars. Cut the foliage off so that there remains
a three to four inch stem on the roots. Because tubers may have
spread quite a distance, begin digging far enough from the plant
so as not to damage the tuber. A spading fork or spade works well
for this task. For easier lifting, make several cuts into the soil
with the fork or spade around the clump and gently pry to raise
the tubers intact.
the tubers are out of the soil, remove as much soil as possible
without damaging the tubers. Turn the tubers upside down to drain
the stem and allow the soil to dry. When dry, remove the remainder
of the soil. Soil may also be washed from the tubers with water
under pressure. Cut off any small roots. Remove and discard tubers
that are damaged or diseased and dust any cut surfaces with sulfur.
Place the tubers in wooden flats, bushel baskets or cardboard boxes
that have a few inches of peat moss, sawdust or vermiculite in the
bottom. Cover with the same packing material, leaving the stems
A little moisture may be added to prevent shriveling. Place the
packed tubers in a dry, 40 to 55 degrees F location.
tubers in a few weeks and again in January for signs of shriveling
or fungal infection. Add a small amount of moisture if shriveling
has occurred. Do not expect 100 percent survival.
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.
Cuttings may be taken from new growth but do not cut below the first
set of leaves. Cuttings should be three to four inches long. Dahlias
may also be propagated from seed. This method is used most often
for bedding dahlias. Because of cross-pollination, they will not
come true to cultivar. Harvest seeds in September and October. Cut
the ripened flower heads open and lay them out to dry on shallow
trays. When dry, the seeds will readily separate form the chaff.
Store them in sealed containers. Seeds can be sown indoors in February
or March; germination takes about one week.
from Jack Kerrigan, Ohio State University Extension, 2000