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New Guinea
Impatiens (NGI) are relatively easy to propagate. Providing
the appropriate cultural conditions is the key to successful
root system development. In North America, most NGIs are propagated
during late fall and early winter when light intensities are
low enough that additional shade is not required. These same
low light, cool temperature conditions impact the speed of rooting
and create conditions favorable to insects or diseases that
may attack the crop. Starting with good quality cuttings from
reliable suppliers is your best defense for preventing problems.
CULTURAL
REQUIREMENTS
Media
Choose a
sterile, well aerated propagation media. Mixes that are predominately
peat moss tend to hold too much water and should be avoided
or blended with other components to yield a more favorable propagation
medium. Inorganic media, such as Oasis® or Rockwool®,
work equally well.
Bottom
Heat
Bottom heat is an important factor in promoting healthy root
development. Provide media temperatures of 70-75°F/21-24°C
for best results. Monitor root zone temperatures frequently
as the application of mist may cool the media and slow root
development.
Rooting
Hormones
The use of rooting hormones is optional as most NGI cultivars
root easily without them. However, not all cultivars respond
equally in propagation, and use of these hormones can be beneficial
if rooting a number of different cultivars. Liquid or powder
formulations work well when used at rates suggested for herbaceous
plants.
Temperature
Management
Provide air temperatures of 68-72°F/20-22°C at night
and 70-80°F/21-26°C during the daytime.
Mist
Application
Mist applications on NGIs should provide adequate moisture to
prevent wilting of cuttings, yet allow cuttings to stay dry
enough to avoid rot. Treat these plants as you would geranium
cuttings when setting mist clocks. The most common cause of
rot in young NGI cuttings is overmisting, which can result in
Botrytis and other fungal diseases.
TROUBLESHOOTING
IN PROPAGATION
PROBLEM:
Cuttings rot in propagation
POTENTIAL
CAUSE:
Diseases: Botrytis (can result from damaged cuttings
or cuttings with open flowers), Myrothecium (leaf spot), Rhizoctonia
(maybe the result of contaminated rooting media) or Erwinia
Cultural: Excess mist application
Other: Rot beginning at the base of cuttings and moving
upward may indicate rooting hormone was not properly diluted.
PROBLEM:
Leaves curl downward, making it difficult to plant cuttings
POTENTIAL
CAUSE:
Cultural: Cold temperature or DIF in propagation causes
leaves to reflex downward and hold cuttings above the rooting
media
Other: Cuttings may have been harvested from stock plants
treated with Florel®
resulting in a downward leaf presentation similar to plants
exposed to DIF.
PROBLEM:
Cuttings fail to develop roots
POTENTIAL
CAUSE:
Insects: Fungus gnat larvae may be feeding on the tender
new roots as they form
Cultural: Rooting media temperature is too cold, may
be aggravated by excess mist application
Other: Cuttings may have been harvested from stock plants
under stress, affecting the performance of these plants.
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