Plant of the Month for May: Impatiens

As summer approaches, it is likely that we will be getting a bit more rain. Maybe it’s time to consider putting in a rain-loving bedding plant that will fill your garden beds with colorful flowers all summer. Several varieties of impatiens can provide flower as well as leaf color while enjoying the summer rains.

Two different impatiens species can be easily found and grown here in West Hawaii. Both are in the small Balsaminaceae or Impatiens family that includes about 850 species. The smaller of the two species, Impatiens walleriana, is a low growing bedding plant that features many different flower colors. It is native to eastern Africa and is known as impatiens. The more shrub like Impatiens hawkeri is native to New Guinea and parts of the Solomon Islands. Though its flowers are similar in color to impatiens, New Guinea impatiens are distinguished by a variety of leaf and stem colors.

The standard impatiens has been cultivated in Hawaiian gardens for many years. It is a somewhat succulent, herbaceous plant that grows best in part to full shade and will wilt noticeably if it doesn’t get adequate water. It does well when planted en masse on a slope or in an area that is shady most of the day. It is well suited to container growing as well but requires moist soil that drains well.

Impatiens flowers nearly year-round here in the tropics and produces a profusion of seeds following flowering. This has caused it to become somewhat invasive in some upland areas that have frequent rainfall. Her cousin, the New Guinea impatiens is low on the invasive species list and for that and many other reasons is my preferred variety.

Several New Guinea impatiens varieties were first brought to the U.S. in the early 1970s. They proved to be a bit hardier than the standard and can tolerate more sun and slightly drier conditions. None are drought tolerant, however. It is not such a prolific seed producer and asexual propagation from cuttings requires nearly a month to establish new plants.

Horticulturists have been able to create many new varieties, however, with careful crossing of the first few that arrived. Hundreds of new impatiens cultivars are now available with wide variations in flower, stem and foliage size and color. Some of the crosses have produced bicolor flowers as well. The new varieties also have greater heat and water stress tolerance and may have a more compact growth habit. If you buy plants from a nursery, be sure to check the tag for the best growing conditions for that variety.

Some of the new varieties have leaves ranging from deep bronze to dramatic combinations of white variegation with red mid ribs, green edges and purple undersides. Add to that blooms in purple, lavender, coral, deep red, hot pink and bright orange and you have a nearly full palette of color available in a single species. Pure white flowers also make an attractive display growing among the dark green leaves of some of the varieties.

The New Guinea impatiens can provide a colorful base under larger shrubs or trees. They can grow to nearly twenty-four inches tall with an equally wide spread when grown under the right conditions. They also are attractive as mass plantings where afternoon shade is available. Attractive pots or hanging baskets are also great locations for these plants. They will do well as house plants if placed near a window with partial sun exposure.

Both the standard impatiens and the New Guinea can be easily propagated from cuttings. A cutting of at least four inches with several nodes is a good start. Dip the cut end in rooting hormone and place it in a moist medium of 50% of each perlite and vermiculite for best results. Keep the cuttings in a shady spot until they “take.” It may be at least a month before the cuttings produce roots and new growth.

Once new growth appears you can ‘harden off’ your plants by placing the pots in their new location for several hours a day. After about a week of increasing their hours of outdoor exposure, they are ready to install in your landscape.

Plant them in loose soil that is about 30% organic matter and has a slightly acid pH between 6 and 6.5. Adding a small amount of fertilizer and some amendments like green sand can improve the soil quality and encourage new growth. Bone meal or other fertilizers high in phosphorus will help root development if applied in the root zone during transplanting.

Providing wind protection and shade from hot afternoon sun provides the best conditions for plant heath and flower production. Too much sun can cause pale or burned leaves as well as flowers that are small and hidden in the foliage. Daytime temperatures between 70 and 85 degrees and nighttime temperatures between 55 and 65 are best for the New Guinea impatiens.

For healthy plants, be sure that the soil is consistently moist but not soggy. Dry soil can result in wilting and loss of flowers. Soil that is too wet can cause root and stem rot. Drip irrigation might be best for all impatiens varieties so that adequate moisture gets into the root zone.

Though downy mildew nearly wiped out all of the standard impatiens a while ago, many resistant varieties are currently on the market and most of the New Guinea varieties and the new cultivars are also resistant.

Because impatiens prefer moist soil, they are occasionally susceptible to fungal root and stem diseases. Taking care not to overwater and reducing any standing moisture can avoid this problem. In severe cases, using the most environmentally friendly fungicide is a good way to treat these problems.

Though you can cut back the standard impatiens to control growth, deadheading is not need as the plants are self-cleaning which means that dead flowers fall off on their own. You can prune a few inches off the top of the plants once they are at least six inches tall to create a bushier plant with more flowers. Cleaning up any old fallen flowers can prevent molds from developing.

New Guinea impatiens can be kept attractive by trimming the foliage to maintain their compact bushy shape and by removing old flowers periodically.

The most common insect pests of impatiens include aphids and the tiny spider mites that may appear on the underside of the leaves in a delicate webbing. Spider mite damage resembles tiny pinholes on the leaves. Spraying the insects with a combination of horticultural oil and soap in water can control both insects. Best to apply the spray late in the day and wash it off in the morning to prevent leaf burn from hot sun.

Though impatiens may not do well at lower elevations in West Hawaii, the New Guinea varieties can survive with special care and attention at hot, dry locations. The rewards of their colorful presence in shady locations will likely overshadow the extra care lowlanders might need to provide. In partial shade with moist soil at elevations above 1000’ can provide a lovely landscape addition with little care.

Most impatiens varieties are available in local nurseries and garden departments. You’ll likely find several varieties in 4” pots as well as larger specimens. Even the small plants are probably covered in flowers and ready to plant where their colors can be fully appreciated as they grow. Enjoy a flower filled summer by planting some impatiens in your garden.

Gardening events

Saturdays: Work Day at Amy Greenwell Garden, from 9 a.m. to 12:30 p.m. Meet at the Garden Visitor Center across from the Manago Hotel in Captain Cook. Come with a mask and prepared to practice social distancing. Volunteers can help with garden maintenance and are invited to bring a brown bag lunch. Water and snacks provided. Visit the website www.amygreenwell.garden/get-involved/volunteer-1/ and sign up for the weekly email for more information on work days.

Wednesday, May 8: “Webinar by Hawaii Small Business Development Center” on Analyzing Financial Statements – focus on Income Statement – go to Events and Workshops at hisbdc.org for more information and to register. Fee $15.

Thursday, May 9: Richard Stevens at Amy Greenwell Garden starts at 5:30 p.m. at Hale O Pulelehua at Amy Greenwell Garden in Captain Cook. Richard will talk about the new Palamanui Forest Peserve and Botanical Garden and more. An Ethnobotanical Pupu Potluck with attendees offerings will follow. Please RSVP at info@amygreenwellgarden. For more information call the Garden at 808-323-3318.

Wednesday, May 15: Starting a Business in Hawaii, from 9 to 10:30 a.m. online webinar. Registration fee is $15. Register at https://go.hawaii.edu/FX4. Presented by East Hawaii Small Business Development Center.

Thursday, May 16: Business Model Canvas to Business Plan, from 9 to 10:30 a.m. online webinar. Registration fee is $15. Register at https://go.hawaii.edu/NXF. Presented by East Hawaii Small Business Development Center.

Thursday, May 16: Respirator Training and Use, from 9 to 10:30 a.m. at UH CTAHR Extension Office in Kealakekua or online for respirator use training. From 10:30 a.m. to 3:30 p.m. free medical evaluation and respirator fit test (in person in Kona by appointment only). You must ​register to receive information on medical evaluations and respirator fit testing. Register by calling 808-322-0164 or at https://bit.ly/3TJLlei

Saturday, May 18: 14th Annual Mango Festival, from 10 a.m., to 4 p.m. at Hale Halawai in downtown Kailua-Kona. For more information Contact Randyl at randylna@earthlink.net or text or call Randyl Rupar at 808-936-5233. Vendor forms available at https://hawaiianwellness.com/events.

Tuesday, May 21: Hawaii Invasive Species Mini Conference, webinar starts at 9:30 a.m. Topic: Coconut Rhinoceros Beetle. For more information go to Hawaiian Invasive Species Council website or call Roshan at the UH Extension Service office at 808-322-4892.

Save these dates

Wednesdays – May 29 to Aug. 3 (10 weeks): Ag Orchard Cohort, 5:30 to 7:30 p.m. (online), Saturdays from 8 a.m. to 2 p.m. in Oahu orchards. Cost $200. Learn how to plan, plant and manage a productive commercial orchard. Contact gofarmhawaii.org for more information or to apply.

Wednesdays, June 12 – July 6 (4 weeks): Agrifloristry, 5:30-7:30 p.m. (online), Saturdays 8 a.m. to 2 p.m. Various locations around Oahu, Cost: $150. Learn ways to plan your flower farm. Contact gofarmhawaii.org for more information or to apply.

Thursday, Friday and Saturday, July 18-20: 29th Annual Hawaii Coffee Association Conference, at the Ala Moana Hotel in Honolulu. Currently seeking lecturers and conference volunteers for the Trade Show and Statewide Cupping Competition. Check their website for more information at https://hawaiicoffeeassoc.org/Conference-2024.

Farmer direct markets

(Check websites for the latest hours and online markets)

Wednesday and Friday: Ho’oulu Farmers Market, 9 a.m. to 2 p.m.- Sheraton Kona Resort at Keauhou Bay

Saturday: Keauhou Farmers Market, 8 a.m. to noon at Keauhou Shopping Center; Kamuela Farmer’s Market, 7:30 a.m. to noon at Pukalani Stables; Waimea Town Market, 7:30 a.m. to noon at the Parker School in central Waimea; Waimea Homestead Farmers Market, from 7:30 a.m. to noon at the Waimea middle and elementary school playground.

Sunday: “Pure Kona Green Market” 9 a.m. – 2 p.m. at Amy Greenwell Garden in Captain Cook; Hamakua Harvest, 9 a.m. to 2 p.m. at Hwy 19 and Mamane Street in Honoka‘a.

Plant advice lines

Anytime: konamg@hawaii.edu

Tuesdays and Thursdays: 9 a.m. to noon at UH-CES in Kainaliu, 322-4893, or walk in Mon., Tues. and Fri: 9 a.m. to noon at UH CE.

Diana Duff is a plant adviser, educator and consultant living part time in Kailua-Kona.