New Guinea Impatiens Care for the UK Gardener

Contents

• History
• Why New Guinea Impatiens?
• New Guinea vs. Seed Impatiens
Home Culture Tips for New Guinea Impatiens
• Pre-planting Care
• Preparation of Soil. Beds. and Pots
• Location
• Planting
• Watering
• Feeding
• Removal of Old Flowers
• Pest and Weed Control

History

New Guinea Impatiens are native to New Guinea, an island north of the continent of Australia. Their introduction into the commercial horticultural industry is rather recent, with the first commercial varieties appearing on the market in the early 1970s. The first plant specimens used in commercial breeding were collected from a joint plant exploration to New Guinea involving the United States Department of Agriculture and Longwood Botanical Gardens in Pennsylvania in 1970. These early specimens were somewhat gangly and poor flowering, but were unique in their brightly coloured foliage and relatively large flowers. From these initial plant specimens and early breeding lines, New Guinea impatiens have been transformed into one of the most popular landscape and flowering potted plants for consumers. These modem varieties have extra-large flowers, excellent branching, and are easy to grow.

Why New Guinea Impatiens?

There are few crops that have been introduced into the horticultural industry that can compare to the success of New Guinea impatiens. Their popularity has soared over the past twenty years and consumers can select from a wide range of flower and leaf colours. Their popularity and success is primarily due to the plant's extra large, round flowers that are both colourful and visually attractive. Gardeners around the world love the overall beauty and versatility of New Guinea impatiens. They are commonly available for consumers in a wide range of pot sizes and hanging baskets, and are appropriate for landscape beds, patio containers, and mixed combination plantings. With adequate care, they will provide the homeowner and gardener with continuous colour the entire growing season.

New Guinea vs. Seed Impatiens

New Guinea impatiens (Impatiens x hawkeri) differ from the popular elfin (bedding-type) impatiens (Impatiens wallerana) in several ways. New Guinea impatiens are started from vegetative cuttings and are difficult to propagate from seed, while elfin impatiens are easily and most commonly grown from seed. Elfin impatiens have smaller, but more numerous flowers than New Guinea impatiens and are most commonly used in landscape bed plantings. New Guinea impatiens, while used in landscape beds, are also very popular as holiday potted plants and for large outdoor containers. Both types of impatiens require similar growing conditions, such as a good, well-drained soil, adequate moisture, and afternoon shade.

Home Culture Tips for New Guinea Impatiens

Pre-Planting Care

Make sure to only purchase mounded, well-branched plants that have healthy root systems, smooth shiny leaves and many flower buds. A void tall, stretched plants with yellowing or dead foliage and poor root development (brown roots). This generally is a sign that the plants have not been adequately watered or cared for at the retail store.

When you get the plants home, don't let them dry out before planting. If you can't plant them immediately, place them in a bright location but avoid full direct sun. Although New Guinea impatiens like shady conditions, do not store them in very dark areas, like a garage, for more than a day or two.

Preparation of Soil. Beds. and Pots

Pots, baskets, window boxes, or other containers should be thoroughly cleaned and disinfected before use. A good disinfectant is 1 part Clorox to 9 parts water. The pots should be cleaned well with the solution and hosed off with fresh water to remove any residue that would harm the plants. If a disinfectant is not available, then wash the containers out with a soap solution and rinse well with fresh water. The pot size should be approximately 1.5 times the diameter of the potted pot purchased. Plants in 1.5L pots should be planted into a 2 – 2.5L containers. Three to four 15cm plants should be potted into a 3.5 – 4L containers. It's a good idea to ask your garden centre about the varieties. Some variety lines, like the Super Sonics, are more vigorous growing than other lines, like Paradise or Sonics, and should be planted in bigger containers. For maximum growth, your soil should provide adequate drainage.

When planting in containers it is best to use either a Tub and Basket compost or a Multi Purpose with added John Innes compost, your local garden centre is the best source for these.

These types of growing media are designed for long term planting in containers and both will give excellent results. The tub and basket should contain moisture retaining granules to hold onto moisture and nutrients and it is completely peat based, the Multi purpose with added John Innes is a  mixture of peat and loam based composts, the theory being that the loam acts as a moisture retainer as well as adding weight to the compost to make it suited for planting recipes that include taller plants( the bulk of the john Innes adding weight to the container and countering wind rock).

Prior to filling the container with compost it is advisable to cover the drainage holes in the bottom with crocks (broken terracotta pots) this will help to improve drainage, counter waterlogging and stop the compost from leaking out of the pot.

 It is also advisable to add a controlled release fertiliser such as osmocote at the time of planting to ensure a steady supply of nutrients during the growing season. 

For container gardening use only high quality commercial potting soil - do not use field or garden soil or poor quality inexpensive potting soil. The best soil is mostly coarse peat moss with vermiculite and perlite. Avoid soils that have bark or wood chips unless it is well composted.

If planting into flowerbeds, make sure to loosen the soil, and to add 30-50% compost or peat moss for increased drainage. Incorporate 1 pound of a complete dry-formulated fertiliser for every lOO-sq. ft. of bed at the same time. Slow-release (controlled-release) fertilisers also work well and can be either incorporated into or top-dressed on top of the soil bed or container media.

Location

New Guinea impatiens can tolerate full sun in the UK climate.

New Guinea impatiens should not be set outside until night temperatures are above 7 degrees C.. They are not as cold hardy as many other annuals, such as geraniums or petunias. They grow best with day temperatures of 24 to 30 degrees and night temperatures of 13 to 18 degrees. If day temperatures are higher, providing extra shade in the hot afternoon hours and protecting the plants from drying winds will help reduce stress.

New Guinea impatiens can be used in variety of ways in the garden. They can be planted in mass plantings, but are also popular in a wide range of patio containers. They make a perfect choice for brightening up covered porches and other shady areas, and are becoming more popular in combination plantings with other annuals. New Guinea impatiens can also be grown inside if placed near a window with full sun.

Planting

The planting should not be done during the hot hours of the day. The plants should be planted at the same level of the original potting soil. Water heavily immediately after planting. Providing a mulch around the plants will help cool the soil and conserve moisture during the hotter summer months.

As a rule of thumb, for proper spacing in flowerbeds, allow enough space in between the plants to accommodate the same diameter of the plants you are planting. For example, space 10cm  pots on 20 – 22cm centres, 13cm pots on 25cm – 28cm centres, and 15cm pots on 30cm – 33cm centres. Again, know your varieties and plant more vigorous varieties a little further apart. Most compact-medium growing varieties will reach a final height between 25cm –30cm while more vigorous varieties will reach up to 40cm in height.

Watering

New Guinea Impatiens prefer soil that is consistently moist but not soggy. Do not allow the plants to dry out completely. This will result in wilting and loss of flowers. If possible, avoid watering over the tops of the plants and flowers. Cut back on your watering frequency when conditions are cool and cloudy and the plants are still small shortly after planting. During these times the water requirements of the plants are relatively low until the plants become better established and the warmer weather arrives.

When the plants are actively growing, light rain showers or occasional sprinkling of the foliage does not provide enough moisture to constitute proper watering when the soil is dry. Although New Guinea Impatiens wilt easily under water stress, they usually recover very quickly when given additional moisture. Consistent wilting, however, will result in poor flowering and burnt foliage. For best results, water well, keep the soil moist, and avoid plant wilting.

New Guinea Impatiens do not demand a lot of feeding to keep them growing and performing well in the garden. A long-term, controlled-release fertiliser can be mixed into the soil before planting or applied around the base of the plant after planting. Common brands include  Osmocote, or Nutricote. The draw back with these methods is that it is hard to see (unless you are experienced) when the fertiliser is used up, or leached out by rain and irrigation. If controlled-release (resin-encapsulated) fertilisers are used, it is recommended to use them at the low to medium rate and with a slow 9-month release, as other formulations can release nutrients too fast under the hot summer conditions.

A preferred way to fertilise is to apply water-soluble complete fertilisers that include micro nutrients every third watering at the low end of the recommended rate. This method is more time consuming but supplies fertiliser to the plants at a more programmable rate. If plants are completely dry, irrigate with plain water before fertilising, otherwise the roots might get burned.

Although not required, New Guinea impatiens maintains better overall attractiveness when old flowers are removed periodically. The plants shed their flowers naturally, but sometimes this can lead to messy plants and possible Botrytis fungal gray mold on the old, fallen flowers. Sometimes all that is needed is to shake the basket or container so that the old flowers fall to the ground.

If the plant is getting over-grown and leggy, it can be trimmed back to help keep a compact and bushy shape. Cut the stems back to a leaf node and provide good growing conditions to help the plant recuperate and re-flower.

Pest and Weed Control

The flowerbeds and containers should be kept free of weeds and monitored for pests. The most common insect pests are:

Aphids - small green ovate insects, usually clustered together at the growing tip of the plants. A good indication of aphid damage is the "black sooty mold" on the leaves. This is a fungus that grows on the plant sap excreted by the aphids.

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These guidlelines were originally developed by Fischer USA for the www.fischerusa.com website but have been adapted for the UK climate and conditions.