By Graham Clarke Thursday, 26 July 2007
This charming, long-flowering genus looks good in borders and hanging baskets.
There are some 50 species of Diascia in existence and they have increased rapidly in popularity in the past 15 years. These annuals and perennials from South Africa are small, prolific, long-flowering plants in a range of growth habits and flower colours. The trade has labelled them as patio plants, but they are much more than this.
Diascias often have a spreading, suckering habit. Their upright or sprawling stems are lined with pairs of small, toothed leaves, varying from heart-shaped to thread-like. The slender stems are topped with clusters of open-centred, five-lobed flowers 1.5-2cm across, with two backward-pointing spurs — and because of this, Diascia is also known as twinspur.
At the base of the upper two lobes are two yellow windows, often almost merging into one. Diascia is often confused with Nemesia, which can be distinguished by having just one spur.
The flowers of most species come in shades of rose-pink, but the cultivars now available encompass lilacs, deep reds, salmons, oranges and white.
The long flowering season is one of the main attractions of diascias. Plants rarely set seed in the UK because of the climate and the lack of suitable insect pollinators, and this helps to prolong flowering.
Young, vigorous plants produce the best displays. When flowering ceases, most diascias can be encouraged to flower again if trimmed back and given extra fertiliser and water.
Diascias grow well in semi-shade but flower better in full sun. In well-drained soil, they will survive several degrees of frost, although plants often look miserable in cold weather. They vary in their hardiness.
D. barberae, D. fetcaniensis and D. integerrima Award of Garden Merit (AGM) seem to be the hardiest of the species, with D. ‘Appleby Apricot’, D. ‘Ice Cracker’ and D. barberae ‘Ruby Field’ AGM considered the hardiest cultivars.
When diascias first became popular, beginning with the appearance of ‘Ruby Field’ in the 1970s, they were viewed as perennials on the borderline of hardiness. Now it is mainly as plants for containers that their popularity has grown, with series such as Sun Chimes, Wink and Whisper introduced specifically for hanging baskets. The neater forms are also ideal at the front of borders and trailing types look good billowing over a low retaining wall.
New cultivars are introduced every year and these increasingly tend to have flowers close to the mat of foliage rather than held on upright stems high above the leaves.
Things to watch out for include aphids, which may infest young shoots. Slugs and snails can also be a problem and — if the conditions are poor — diascias can be susceptible to Botrytis.
What the specialists say
Christine Boulby, Diascia National Collection Holder, Northumberland “These are such charming plants and people do tend to fall in love with them easily. Some are perennials that tend to get cut short by our winters, even mild ones, so you would think they were annuals.
“To succeed with diascias you should give them a sandy, free-draining soil, which is exactly the sort of conditions they endure in their native South Africa.
“Our National Collection, although in Northumberland, is only a mile from the coast so we do not get too many frosts. This suits Diascia very well, and we suffer relatively few winter losses.
“The plants have been marketed by the trade over the past decade or so as ‘patio’ plants, and so you will mostly see them growing as annuals in pots and hanging baskets. In a border situation, however, they can be very impressive plants, especially if they are allowed to spread their stems in between and through neighbouring shrubs.
“‘Ruby Field’ is an excellent form and is special as it was one of the originals. D. integerrima Award of Garden Merit (AGM) is a hardy, wiry plant, with pink flowers from June to October, requiring little attention. Another excellent form is D. rigescens AGM. Although it is a bit tender, it is a good ‘doer’ and makes an important statement in the garden.”
Stuart Lowen, marketing manager, Ball Colegrave, Oxfordshire “Diascia is susceptible to Botrytis, so avoid high humidity and wet foliage. When the plants are young, allow the media to dry slightly between watering.
“The D. Whisper series is great for 12cm pots, patio containers and hanging baskets. The D. Wink series offers plants with a compact habit, with a great performance in large containers. They need a well-drained, disease-free, soil-less medium, ideally with a media pH of 5.6-6.0.
“The best way to control the growth of Diascia is to grow the crop cool, provide bright light and apply moderate, regular water stress to promote flowering and reduce unwanted vegetative growth. Pinch plants back seven to 10 days after transplanting to improve basal branching. For a larger basket or container a second pinch can be applied.”
Peter Jackson, director, Scotsdale Garden Centre, Cambridge “We plant up a low dish of diascias for the period when they are at their best, and this works very well to get the attention of the customer. We also tend to include them on our alpine benches —they appeal to the same sorts of gardeners, and are ideal for pots and containers.
“But the thing to watch is the watering. There are a number of plants that, for us, do not sit well under our normal automatic watering regimes, and diascias are one of them. They must not get too wet, so hand watering, when absolutely necessary, is best.”
Species and cultivars
• D. ‘Appleby Apricot’ bears apricot-pink flowers from June to October.
• D. barberae displays soft pink flowers held on slim stems above light green foliage. It reaches 20cm.
• D. barberae ‘Belmore Beauty’ is a variegated version of ‘Ruby Field’, has a trailing habit and is good in baskets.
• D. barberae ‘Blackthorn Apricot’ Award of Garden Merit (AGM) carries masses of apricot flowers between June and September.
• D. barberae ‘Fisher’s Flora’ AGM has pink flowers from May to September, on stems reaching 15cm.
• D. barberae ‘Ruby Field’ AGM is one of the best-selling with pink flowers from June to October. It reaches 20cm.
• D. Blue Bonnet is the first to have been bred with some blue starting to show in the petals. It is almost grey over pink; the blue colour seems to come in cooler temperatures.
• D. Coral Belle AGM has deep salmon- orange flowers from June to October. It reaches up to 30cm.
• D. fetcaniensis is a creeping species, carrying rose-pink flowers from summer to autumn.
• D. fetcaniensis ‘Daydream’ is hardy and highly floriferous. It has mid-pink flowers and grows to about 30cm.
• D. Iceberg was bred by Hector Harrison using D. integerrima ‘Blush’ and other plants. It carries white flowers.
• D. Ice Cracker displays white flowers from June to October.
• D. Ice Cream features cream flowers from June to October.
• D. integerrima AGM is a hardy, wiry plant, with pink flowers from June to October. It reaches 30cm.
• D. integerrima ‘Blush’ carries pure white flowers throughout summer with slender leaves.
• D. ‘Jacqueline’s Joy’ has good, strong pink flowers and a neat growing habit.
• D. ‘Joyce’s Choice’ AGM has peach flowers from June to November. It needs well-drained soil.
• D. ‘Katherine Sharman’ has olive-green foliage edged creamy white.
• D. ‘Lilac Belle’ AGM carries lilac flowers from June to October.
• D. ‘Lilac Mist’ AGM has mauve-pink flowers from June to November.
• D. Little Dancer has flowers that change from lilac to pink in the summer and reaches up to 15-20cm.
• D. Little Tango features orange flowers from June to October and is 20cm tall.
• D. Pink Panther has pale pink flowers rising above dark green foliage.
• D. Red Ace has deep pink flowers from June to October.
• D. rigescens AGM has thick stems crowded with pink flowers from May to July and often later. It distinguishes itself from other species by a yellow “median keel” of glands on the lower lobe of the flower.
• D. ‘Rupert Lambert’ AGM carries pink flowers on wiry trailing stems from May to October and reaches 25cm.
• D. ‘Twinkle’ AGM bears tight purple racemes of flowers on lush, dark green foliage. A good basket plant.
• D. vigilis AGM displays rich flowers from June to October. It reaches 20cm and is often sold as D. elegans.
• D. vigilis ‘Jack Elliott’ has an upright habit. Salmon-pink flowers smother the plant in late summer and autumn.
• D. Whisper series has been bred for containers and includes ‘Apricot Improved’, ‘Cranberry’, ‘Tangerine’, ‘Lavender Pink’, ‘Salmon’ and ‘White’.
• D. Wink series has been bred for containers and includes ‘Lavender Pink’, ‘Strawberry Improved’ and ‘Garnet Red’.
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