NEW GUINEA IMPATIENS
Scientific Name: Impatiens × hybrida (I. Hawkeri)
Common Name: New Guinea Impatiens
Dr. J. Raymond Kessler, Jr.
New Guinea Impatiens have only recently become popular bedding plants since their introduction to the U.S. in 1972. Most are grown in hanging baskets or as potted plants for transplanting into the landscape or as container plants for the patio or window boxes. The majority of cultivars are currently propagated vegetatively, although seed-propagated cultivars have recently come to the market (Spectra F1 hybrids).
The origin of New Guinea Impatiens started with a joint plant collecting expedition by Longwood Gardens and the USDA in 1970. Several plants were brought back form New Guinea and ordinally given separate species names. However, cytogenetic work has shown that they belong to one species (Impatiens hawkeri) but a lot of variation exists within the species. Crosses with additional species form Java and the Celebes islands has lead to the plants in production today.
The first commercial series was called the Circus series, released in 1972. Since that time numerous series comprised of a hundred cultivars have been released. Most cultivars are patented, so do not take cuttings unless your a licensed propagator. Recent breeding have concentrated on shorter plants, shorted production times, heat and water stress tolerance, and variation in flower and foliage size and color.
Growers may start a New Guinea Impatiens crop in three ways: 1) Order cutting to grow stock plants from which cutting are taken for production, 3) Order unrooted cuttings to root in-house for production, or 3) Order rooted cuttings which are transplanted to the finishing container. It is essential to order the highest quality propagation material that is certified free of disease. New Guinea Impatiens can suffer from tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV) carried in the tissues.
Everything associated with propagation should be sanitized; sterile medium, clear (new) flats, sterile bench tops, and sterilize anything that comes in contact with the cuttings. Many different kinds of propagation media have been used; peat-lite media, vermiculite, perlite, rockwool, but all must be well-drained and not remain saturated. Propagation medium pH should be 5.5 to 6.5 with a low soluble salts (<0.75 mmhos/cm). Light levels in propagation should be 2000 ft.ca. New Guinea Impatiens cuttings should be ¾- to 1-inch long, with no more than 2 fully expanded leaves and 3-4 immature leaves, with -½” stem base to stick into the propagation medium. Propagation temperature are 70-72F night and 75F days, preferably provided as bottom-heat to warm the propagation medium. Mist intervals range from every 15 min. on sunny days to 2 hours on cloudy days for 5 seconds depending on the environmental conditions. Mist at night is usually not required and may be harmful. Propagation timing:
5 to 7 days Callus forms at base of cutting, high mist, temperature during this period.
10 to 12 days Roots about ¼”, reduce mist to about every ½ hour.
3 to 4 weeks Roots adequately developed for transplanting.
Transplant as soon as the cuttings are well rooted to prevent stretching. Fertilizer or growth retardants are not needed in propagation.
Transplanting: The backbone of New Guinea Impatiens production for most growers is the 4″ or 4½” pot with one rooted cutting per pot, though 5″ and 6″ pots may be produced depending on market demand. Five inch pots may have 1 or 2 cuttings and 6″ pots 1 to 3 cuttings per pot depending on cutting costs verses production timing. New Guinea Impatiens may also be grown in Jumbo finishing flats or 3-3½” pots for the mass market. Hanging baskets of New Guinea Impatiens are also popular with 1 to 3 cuttings per 8″ basket, 1 to 4 cuttings per 10″ basket, or 3 to 5 cuttings per 12″ plastic basket.
Medium: Use a peat-lite medium composed of peat and perlite, vermiculite, bark, or rockwool. The medium should be well-drained and aerated, but with slightly more water holding capacity than for some crops. Impatiens as a rule require a lot of water and should never wilt, extra water holding capacity facilitates this goal. Dolomitic lime to a pH of 5.8 to 6.2, superphosphate (4.5 lbs./yd3) , and micronutrients (½-¾ recommended rate) are added to the medium at mixing. Medium pH should not drop below 5.8, especially if manganese and iron concentrations are above 3.0-5.0 ppm because New Guinea Impatiens are sensitive to micronutrient toxicity.
Fertilization: Little or no fertilization is required until the roots of plants in the final container reach the pot margins. Fertilizer on a CLF program at 100-150 ppm nitrogen with the nitrogen level about equal to potassium (150-0-150 to 200-0-200) with no phosphate if superphosphate was added during mixing. If superphosphate was not added to the medium, liquid feed with 50 to 75 ppm P. If fertilizer is not applied at every watering, use 300 to 350 ppm N, 100 ppm P, and 300 to 350 K every third watering. Be careful using a fertilizer containing micronutrients if they were added during media mixing. Micronutrient toxicity cause necrosis of lower leaves or leaf margins, shoot die-back, or distorted, stunted upper leaves. Magnesium deficiency is common and may be corrected using 8 oz. Magnesium sulfate / 100 gal. once per month.
Temperature: Night temperatures should be 68F and day temperatures 75F for the first 2 to 3 weeks. The night temperature can then be dropped to 65F. Night temperatures above 72F can delay flowering. New Guinea Impatiens respond to DIF. Stem lengths increase as the day temperature increase relative to the night temperature (positive DIF).
Photoperiod: No significant response found.
Light: New Guinea Impatiens tolerate higher light intensities than bedding Impatiens. As much light as possible should be provided in the winter and spring. Provide a minimum of 3000-4000 foot-candles during the middle of the day. Low light reduces varigation in the foliage and slows flowering. Apply shading if light exceeds 6000 foot-candles.
Pinching: Newer cultivars are self-branching and require no pinching. Pinching will delay bloom by two to three weeks.
Growth Retardants: Generally not required or used on New Guinea Impatiens. Cycocel, B-Nine, and A-Rest show minimal effect, however, Bonzi is effective at 5 to 30 ppm.
Supplemental Light and Carbon Dioxide: Supplemental light from HID lamps benefits growth at 400 ft.ca. after rooting in propagation. Supplemental carbon dioxide also improves growth at 1000-1500 ppm. A 2-3F increase in day temperature should be used with supplemental CO2.
Spacing: Spacing too close will result in stretching. Newely potted cutting can be maintained pot-to-pot until the canopies begin to close.
Physiological: Low light and low fertility cause mottled foliage. Water stress causes leaf and flower bud abscision.
Pests: Spider mites, cyclamen mites, thrips, mealybugs, and aphids all infest New Guinea Impatiens
Diseases: Pythium, Phytophthora, and all cause root rots. Rhizoctonia causes stem rots. Impatiens Necrotic Spot Virus (INSV) can be very serious and the virus is carried by Thrips. Botrytis can be a problem under cool, humid conditions.
Varies with geographic location, container size, cultivar, climate, and number of cuttings per container, e.g. 4″ pots can be finished in 8-10 weeks in warmer times of the year while requiring 10-16 weeks in low-light, cooler times of the year.