Ames, Iowa
January 28, 2008
By Richard Jauron,
Horticulturist, Iowa State
University Extension
Iowa State University Extension Garden Column for the week of
Feb. 1, 2008
Geraniums have been a popular bedding plant for many years.
Plants are commonly grown from cuttings. However, geraniums can
also be grown from seeds. Seed-grown hybrid geraniums possess
excellent vigor, heat tolerance, disease resistance and are
free-blooming.
Geraniums are relatively easy to grow from seeds. However,
geranium seedlings are slow growing. Geranium seeds should be
sown in early to mid-February to produce flowering plants for
spring. Flowering occurs approximately 13 to 15 weeks after
sowing. Suggested seed-grown geraniums for Iowa include
varieties in the Elite, Orbit, Maverick, and Multibloom Series.
A series is a group of closely related varieties with uniform
characteristics, such as height, spread, and flowering habit.
Generally, the only characteristic that varies within a series
is flower color.
Soilless mixes, such as Jiffy Mix and Redi-earth, are excellent
germination media. During germination, damping-off of geranium
seedlings can be a serious problem. Damping-off is caused by
various types of fungi that attack the seedlings and destroy
them. To discourage this, containers used for starting seeds
should be clean and have adequate drainage. Previously used
containers should be washed in soapy water, then disinfected by
dipping in a solution containing one part chlorine bleach and
nine parts water.
Fill the container with the germination medium to within 1/2 to
1 inch of the top. Firm the medium lightly, water thoroughly and
allow it to drain for a few minutes. Sow the seeds in rows 2 to
3 inches apart and cover with about 1/8 inch of medium. After
sowing, thoroughly water the medium by partially submersing the
container in water. When the surface becomes wet, remove the
container from the water and allow it to drain. The medium also
can be moistened with a soft spray of water from a rubber bulb
sprinkler or similar device.
To ensure a uniform moisture level during the germination
period, cover the container with clear plastic food wrap or a
clear plastic dome. Set the container in bright light, but out
of direct sunlight. Excessive heat buildup may occur if the
covered container is set in direct sunlight. The temperature of
the medium during germination should be 70 to 75 degrees F. With
favorable temperature and moisture levels, the seeds should
begin to germinate in seven to ten days.
Remove the plastic covering as soon as germination occurs. Place
the seedlings in a sunny window or under flourescent lights.
Flourescent lights should be no more than 4 to 6 inches above
the seedlings and left on for 12 to 16 hours per day. Using a
well-drained commercial potting mix, transplant the seedlings
into individual containers when their first true set of leaves
appears. Handle the small seedlings by their leaves since the
small, thin stems break easily. Insert seedlings to the base of
the seed leaves (cotyledons) when transplanting.
For best results, grow seedlings under fluorescent lights. (A
standard fluorescent shop fixture with one 40-watt cool white
and one 40-watt warm white tube works fine.) Plants grown in a
window often become tall and spindly because of inadequate
light. Ideal growing temperatures for geraniums are 70 to 75
degrees during the day and 60 to 65 degrees at night. Thoroughly
water the geraniums when the soil surface is dry to the touch.
If using a commercial potting mix containing a slow-release
fertilizer, fertilization probably won’t be necessary. An
application of a dilute fertilizer solution once every two weeks
should be sufficient for those potting mixes that don’t contain
a slow-release fertilizer.
Harden or acclimate the plants outdoors for seven to ten days
before planting into the garden. Initially, place the geraniums
in a shady, protected location. Then gradually expose the plants
to longer periods of sunlight. Plant the geraniums outdoors when
the danger of frost has passed. In central Iowa, it’s usually
safe to plant geraniums outdoors in early May. |
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