May 2006
Growing Annuals
Prepared by Karen
Russ, HGIC
Information
Specialist
and
Bob
Polomski, Extension Consumer Horticulturist, Clemson University
Images Courtesy
Images
By BA
Annuals
quickly provide more color in the landscape for longer periods of time
than any
other garden plants. They are versatile, sturdy and inexpensive.
GROWTH RATE
True annuals
sprout from seed, flower, set seed and die within one season. Many
flowers
that are not hardy such as begonias, impatiens
and geraniums
are also grown as annuals.
Biennials complete their life cycle in two growing seasons. In South
Carolina many can be
planted as seed in summer or fall to bloom the following spring or
summer. A practical
definition of annuals could be plants that must be replaced every year
in the garden.
Annuals are
commonly grouped as hardy, half-hardy or tender. Hardy annuals — such
as pansies and
ornamental kale — are grown for color in cool and cold seasons. They
are usually planted in the fall. Most decline or die with the onset of
summer heat.
Half-hardy
annuals —such as allysum and dianthus —can tolerate light frost
and are usually planted in early spring for spring and early summer
color. They usually
decline in summer heat but may bloom again in the fall.
Tender annuals
— such as vinca,
zinnia and impatiens
— cannot tolerate
freezing temperatures. They should be planted in the spring after all
danger of frost is
past.
LANDSCAPE USE
Most annuals
need full sun for at least 4 to 6 hours a day to flower well. Choose
shade-tolerant species such as impatiens, coleus or begonias
for locations that receive
less sun.
Avoid planting
in areas where water stands after a heavy rain. Also avoid areas near
large trees and shrubs that may have many thirsty feeder roots.
Good bed
preparation is essential for good performance of annuals. Deeply spade
the
beds to a depth of 6 to 10 inches. Amend clay soils by mixing in at
least 2 inches of pine
bark humus, compost, leaf mold or small pea gravel to improve drainage
and aeration.
Improve water retention in sandy soils by mixing in 2 to 3 inches of
pine bark humus,
composted leaf mold or peat moss. Raised beds can be used to ensure
adequate drainage.
Base
fertilizer and lime applications on the results of a soil test for best
results.
In the absence of a soil test,
add a complete fertilizer such as 10-10-10 at the rate of 1
pound per 100 square feet of bed area or a complete slow-release
fertilizer following
label directions.
A pH of 5.8
to 6.5 is satisfactory for most annuals. Most South Carolina soils are
acidic and require the addition of lime to correct pH. Incorporate lime
and fertilizer
into the top 4 to 6 inches of soil after mixing in the soil amendments.
Rake the soil
surface smooth.
Avoid working
soil while it is wet since this can cause lumping and shallow
"pans," which resist air, water and root penetration. Soil that is
ready for
cultivation holds its shape when squeezed, but crumbles easily.
Most annuals
are grown from seed. They can be direct-seeded in prepared beds,
started
indoors for transplanting outside later or purchased as ready-to-plant
transplants.
The
recommended seeding date, depth and spacing are usually listed with
other
information on the seed packet. Some annuals that are listed for late
winter or early
spring sowing can be planted in late fall in the warmest parts of the
Coast. Most
outdoor-sown annuals should be thinned to a recommended spacing when
they develop the
first pair of true leaves.
If seed is
sown indoors for later transplant, seedlings must be located close to a
light source for at least 16 hours daily. Insufficient light will
result in weak, spindly
seedlings.
Most summer
annuals can be seeded indoors 6 to 8 weeks before the last frost. Seeds
should be sown according to label directions in a sterile soilless mix.
Seedling flats
should provide good drainage.
Wait to plant
tender annuals until the danger of frost has passed. Many annuals, even
if not injured by low temperatures, will not grow well until the soil
warms. Plant winter
annuals at least 6 weeks before expected first fall frost date to allow
time for root
development.
Plant annuals
with the top of the roots just under the surface of the soil. Be sure
to
remove paper, fiber and plastic pots before planting. Remove the upper
edges of peat pots
so that the pot will not act as a wick, pulling water away from the
roots.
Pinch off any
buds and flowers when planting to promote better branching and a
stronger
plant.
Once
transplanting is complete, water the plants thoroughly. Pay especially
close
attention to watering the first few weeks while plants develop their
root systems.
Adequate moisture is essential for the growth of flowering annuals.
Most annuals need at
least 1 to 1½ inches of water per week from rain or irrigation.
More may be needed during
very hot weather.
To promote
deep root growth, water thoroughly and deeply. Allow the soil surface
to dry
before watering again. Soaker hoses and drip irrigation are ideal
watering methods since
they save water and avoid wetting leaves and flowers.
Mulch
flower beds with 2 to 3 inches of pine bark or pine straw to help
conserve soil
moisture and reduce weed growth. Mulches shade weed seeds and prevent
their germination,
eliminating or reducing the need for hand or chemical weed control.
Annual plants
may require additional fertilizer during the growing season.
Water-soluble fertilizers give fast, but temporary, effects.
Slow-release fertilizers are
expensive but convenient and easy to apply without waste. If plant
growth and appearance
looks normal, fertilization will be unnecessary.
As flowers
fade, remove them before seeds are formed to keep plants looking
attractive
and encourage continuing flowering. Heavy pruning can invigorate some
species. For
instance, petunias can be cut back in midsummer to within a few inches
of the ground,
fertilized and heavily watered, and they will be full and attractive
again in just a few
weeks.
PROBLEMS
Annuals vary
in their insect and disease susceptibility. Some are virtually
trouble-free in the landscape while others require considerable care to
look their best.
Choose
insect-and disease-resistant species and cultivars when possible. Keep
the
garden clean and weed-free, and be alert for early signs of trouble to
reduce the need for
pesticides. To prevent the spread of leaf diseases, avoid overhead
watering if possible
and water early in the morning to allow the plants to dry quickly.
Overwatering can lead
to root decay.
A variety of
insect pests attack annuals. The most common are aphids, spider mites,
white flies and caterpillars. Infestations are more easily controlled
early, before the
population has a chance to expand.
There are a
number of pesticides available for controlling insects and diseases of
annuals. Accurate identification of the insect or disease is the first
step. Misuse of
pesticides may cause injury to desirable plants. Always read the label
carefully.
ANNUALS FOR
VARIOUS USES
Prepared by Karen Russ, HGIC Information Specialist, and Bob
Polomski, Extension
Consumer Horticulturist, Clemson University
This information is supplied with the understanding that no
discrimination is intended
and no endorsement by the Clemson University Cooperative Extension
Service is implied. All
recommendations are for South Carolina conditions and may not apply to
other areas. All
recommendations for pesticide use are for South Carolina only and were
legal at the time
of publication, but the status of registration and use patterns are
subject to change by
action of state and fedral regulatory agencies. Follow all directions,
precautions and
restrictions that are listed. (New 6/99)
The
Clemson University Cooperative Extension Service
offers its programs to people of all ages, regardless of race, color,
sex, religion,
national origin, disability, political beliefs, sexual orientation,
marital or family
status and is an equal opportunity employer.
Clemson University Cooperating with U.S. Department of Agriculture,
South Carolina
Counties, Extension Service, Clemson, South Carolina. Issued in
Furtherance of Cooperative
Extension Work in Agriculture and Home Economics, Acts of May 8 and
June 30, 1914
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