New Guinea Impatiens Propagation
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.
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 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.
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.
Provide air temperatures of 68-72°F/20-22°C at night and 70-80°F/21-26°C during the daytime.
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
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
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
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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