Kerria japonica is an easy-to-grow, dependable, deciduous, spring-flowering shrub that provides a cheery burst of colour early in the season.
Occasionally known as the Japanese rose, it is a cottage-garden staple that grows pretty much anywhere. It produces distinctive, single or double yellow flowers in April/May on thin, arching stems along with alternate, serrated, green, oval leaves. Further sporadic flowering may follow later in the season.
This vigorous plant is ideal for shady spaces or north-facing walls and, indeed, is better kept out of strong sunlight, which may bleach the flowers. However, it can become unruly, growing to 3m high and 3m wide if it is not pruned. Fresh growth will also appear from suckers.
Thinning out old shoots after flowering helps the shrub prosper - it will happily withstand even hard pruning. This promotes flowering, which occurs only on fresh growth.
Propagation is simple too. The stems are hollow, so softwood cuttings can be taken immediately below a leaf node where there should be pith in the shoot. It is unfussy about soil type and is largely untroubled by pests and diseases.
Growers' opinions are split over the popularity of the shrub with the public. Some say its hardiness means that its popularity could pick up after this year's hard winter. Others perceive the plant as old-fashioned and say that its vigorous growth makes it something of a nuisance.
K. japonica is the sole member of the Kerria genus, distributed across China, Korea and Japan. It is named after Kew gardener William Kerr, who found the plant during an eight-year plant hunt in China from 1804, a trip that also yielded garden staples Rosa banksiae, Pieris japonica and Nandina domestica Award of Garden Merit (AGM). The modern plant K. japonica 'Golden Guinea' AGM is bigger and brighter than Kerr's original.
Growing Kerria is easy because it is tolerant of shade and neither clay nor lime will bother it, but for the best results plant it in a rich loam. There it will thrive, so prune to remove the old shoots that die back after flowering, or brutally cut out all the flowered branches as they fade, leaving room for the elegant new wands that will bear next year's flowers.
There is also a silver, variegated and less vigorous form, K. japonica 'Picta', with single flowers. This needs less drastic treatment: careful thinning of the oldest shoots is important and you should watch out for any plain-leaved branches because it has a tendency to revert from variegated to green foliage.
WHAT THE SPECIALISTS SAY
Julie Hadley, joint owner, Moreton View Nurseries, Herefordshire "We grow K. japonica 'Pleniflora' Award of Garden Merit (AGM). It's always a reliable plant that performs and flowers well. This year we've had the first proper winter for years. People are more uncertain of planting some things but Kerria is not one you could put in that category so I see it getting more popular this year.
"We don't do a big crop but sell as much as we grow. It flowers for the second time in September and has no real problems. We don't bring it in for the winter and could easily grow more to sell."
Debbie Gooding, sales adviser, St Bridget Nurseries, Devon "Kerria has a lot going for it. It grows in the sun or partial shade and gives no trouble, being fully hardy with no pest and disease problems. However, because it is suckering, it can become a problem if you have limited space. It's not suitable for the smaller garden.
"We used to do the single-flowering 'Simplex' too but now we just do 'Pleniflora' AGM because of its pompom-like flowers. It's one of the slightly old-fashioned ones and not as popular as it used to be. But it gives a rich yellow colour for spring with a pretty shape and delicate arching."
Mark Warburton, nurseryman, Ashwood Nurseries, West Midlands "I think K. japonica 'Golden Guinea' AGM is the best (of the cultivars). It has a slightly bigger flower that is a prettier shade of yellow. It looks nice at the back of a border and rambling over more interesting plants at the front. It's a bit too aggressive for small gardens though.
"Straight Kerria grows up to 2.4m in height and takes no skill at all to grow. It's as tough as old boots because it's basically a weed. It can get rather rampant and invasive so it does need to be cut back. Kerria can look good growing next to some contrasting dark green foliage such as the cut-leaf elderberry 'Black Lace'."
Chris Deakin, senior designer, Deakin Lock Landscapes, Suffolk "I don't use it an awful lot because without proper maintenance it can look tatty and some clients don't like its gaudy yellow colour. But it is a good practical plant and it can brighten a gloomy corner.
"Kerria tends to be a strong grower and brings height to the back of a border. I use straight K. japonica but my business partner Jason Lock says the variegated variety is not as thuggy and is more compact and easily manageable.
"Kerria is a cheery yellow, but a lot of people don't like that colour. As a designer, I find that clients either love or hate yellow.
"It can get pretty unruly and when it's older it does not flower as well and can become a bit of a blob in the border."
- K. japonica 'Albescens' produces creamy-yellow single flowers with irregular shaped petals.
- K. japonica 'Golden Guinea' Award of Garden Merit (AGM) produces very large single flowers that are 5-6cm wide.
- K. japonica 'Picta' has grey-green leaves with a creamy-white margin. It can grow to a height of 1.5m.
- K. japonica 'Pleniflora' AGM is a very vigorous variety with large pompom-like double flowers that are 3cm across.
- K. japonica 'Simplex' is a more delicate, arching shrub with flowers shaped like large buttercups.