Medium and pH:
New Guinea Impatiens perform best in a well-drained Medium with sufficient peat moss for good water retention. A wide range of soil (sterilized) or soilless mixes can be used successfully to produce quality plants. The pH should be 5.6-6.0. If using soil, then the pH should be 5.8-6.5.
Watering:
New Guinea Impatiens transpire a large amount of water, but do not respond well to a continuously water-logged medium. After transplanting cuttings or pinching plants it is best to keep the medium just moist, as over-watering at this time will cause problems. New Guinea Impatiens will tolerate slight wilting without plant damage, though leaf and flower burn will occur if plants are stressed too much.
Nutrition:
New Guinea Impatiens require moderate fertilization. Do not feed New Guinea Impatiens transplants until roots have hit the side of the pots. Soluble salts above 2.0 millimhos may cause severe root damage early in production. Young plants can be fertilized at a rate of 100-50-100 of N,P,K, and mature plants at 200-100-200 of N,P,K. Media should be monitored for soluble salts and pH on a regular basis. New Guinea Impatiens need only moderate levels of micronutrients. Excess minor nutrients will cause die-back of the growing tip, leaf margin necrosis and total plant collapse. Insufficient nutrition may result in yellowing of leaves, leaf drop and small flowers.
Temperature:
Temperature is an extremely important growth regulator for New Guinea Impatiens. Vegetative growth is promoted by night temperatures above 65ºF-68ºF, and flower delay may occur if night temperatures are consistently above 70ºF. Cool night temperatures of 60ºF-65ºF reduce stem elongation, encourage branching, and promote flowering. All New Guinea Impatiens do best with a minimum night temperature of 68ºF for about the first two weeks to promote root growth. Once the desired plant size is obtained, night temperatures may be reduced accordingly. Care should be taken to properly vent when growing with cool nights. High humidity and cool temperatures are ideal conditions for Botrytis infection.
Light Intensity:
Maximum light intensity is recommended in early to mid-spring for optimal growth. Light shade should be used in late spring, but light intensity should be between 3,000 and 5,000 f.c. High light promotes growth, increases leaf variegation and intensifies leaf color of the cultivars with dark leaves.
Growth Regulators:
Using lesser amounts of water and fertilizer will have an impact on stretch if done carefully. Negative DI.F. (difference of day and night temperatures) will also work on New Guinea Impatiens to some degree. New Guinea Impatiens will respond to Bonzi® as a foliar treatment. Use between 5 and 30 ppm depending upon growing conditions and cultivar.
Insects:
The two-spotted spider mite, Cyclamen mite, and the western flower thrip are the main insect problems. Pentac®, Mavrik®, and Kelthane® will provide control of mites. Thrips are harder to control, but some insecticides which have proven effective are Conserve®, Thiodan®, Duraguard®, Orthene®, Avid®, Margosan-O® and Tempo®. As always, spray a small test area before applying a new insecticide to a crop.
Diseases:
Good sanitation practices are the best control for fungal diseases. Watering plants early in the day and venting in the afternoon will help control Botrytis. Effective chemicals to control this disease would include Chipco® 26109, Daconil®, Cleary 3336®, and Ornalin®. New Guinea Impatiens may become infected with root rot especially when plants are over watered. A preventative drench of suitable combination of Domain®, Subdue®, Truban®, Cleary 336®, or Banrot® will reduce these disease problems.
Scheduling:
This can vary greatly depending upon season, locale, and desired quality at finishing. One plant per 4" pot requires 6 to eight weeks. One pinched or three unpinched plants per 6" pot requires 7 to 9 weeks. Three pinched or unpinched per 10" hanging basket required 10-14 weeks. Growing conditions and experience will help determine the best schedule for you.
Spacing:
To obtain even growth and good branching, New Guinea Impatiens must be spaced. Space pots when leaves begin to overlap to the next pot. Final spacing for 4" pots is 6", 6" pots is 10", and 10" hanging baskets is 18" centers.