(Editor's Note: This article was originally published on August 8, 2007. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
When it comes to deciduous shrubs (and really all plants) gardeners in northern areas, like myself (zone 5b), have more restrictions placed upon us than those gardeners in more southern climes. With our short growing season, flowering shrubs are particularly important but many of these have rather limited blooming periods, sometimes only a couple of weeks. We need and appreciate shrubs that offer interest all summer. This is where shrubs with colourful summer foliage come into play. Among these are shrubs with yellow, purple-red or variegated foliage. Plant breeders recognize the need for such foliage plants and every year, new selections are being released. We now have plenty to choose from, even for us northern gardeners. This three part series of articles will discuss each of these colour groups and which deciduous shrubs are best suitable to zones 5b or colder.
Part one will deal with yellow-foliaged shrubs. While growing up, it seemed the only yellow-foliaged shrubs available in my local nurseries were golden elder and ‘Goldflame' spirea. Today, we have many more yellow-foliaged shrubs to choose from. They are available in a variety of sizes from dwarf (under 30 cm) to large shrubs (over 4 m) so virtually all gardens, large or small, can have the option of growing a yellow-foliaged shrub. These shrubs blend admirably with other warm colours like oranges and reds or can be used as a strong contrast with cool colours like blues and purples. As a general rule, yellow-foliaged shrubs need full sun to develop the strongest colour. However, in part shade the foliage will become chartreuse which in itself, can be a very attractive colour in the landscape.
For simplicity, I'll describe the various yellow-foliaged shrubs alphabetically, starting with barberry. For many years, Japanese barberries, Berberis thunbergii, were restricted from sales due to the belief that they were an alternate host for wheat rust. However, as it happens, while some barberry are indeed an alternate host for wheat rust, Japanese barberry is not, so the restrictions have been lifted and this wonderful shrub is once more available. Plant breeders have jumped at this and in recent years, there have been a host of new barberry cultivars, both yellow and purple-red foliaged. The old standard yellow barberry were ‘Aurea', which reaches 1.5-2 m, and ‘Aurea Nana' which reaches to 1 m. Both of these are prone to leaf scorch in hot areas. Today we have a wonderful selection of scorch-resistant cultivars. Among the taller selections (1.2 m) are 'Sunsation' and 'Pow-Wow'. While 'Sunsation' is brilliant yellow, 'Pow Wow starts off creamy-yelow but turns chartreuse. ‘Bogozam' (aka Bonanza Gold) has a dwarf, rounded habit to 45 cm while ‘Monlers' (aka Golden Nugget) is even more dwarf (30 cm) with tiny leaves. ‘Golden Devine' is very similar to ‘Monlers'. ‘Golden Carpet' is the newest and has an almost prostrate habit. For a narrow, fastigiate growth habit, you can try ‘Golden Torch' (1.5 m) or ‘Golden Rocket' (1.2 m). All of these are rated for zone 3 and will turn orange shades in the fall. They also produce red, tear-drop shaped fruit that can provide fall and early winter interest.
Some of the yellow-leaved barberry selections include 'Aurea Nana', 'Gold Nugget' and 'Pow Wow'
Among the red-twigged or Tatarian dogwoods, Cornus stolonifera and C. alba, the old standard yellow-leaved variety is ‘Aurea'. This one will reach 2 m and can burn in a hot site. It does have the added bonus of bright red twigs which can be attractive in the winter landscape. More sun-resistant cultivars are ‘Morden Amber' with dark red twigs and ‘Prairie Fire' with orange-red twigs. If space is more limited, the cultivar ‘Garden Glow' is the best choice, but even this one will reach 1.2-1.6 m. Thankfully, they take well to pruning so all of these can be kept smaller than their ultimate height would suggest. They will produce small clusters of white flowers in late spring but they are not particularly noticeable against the yellow foliage. As a group, these dogwoods prefer a damp site and are rated for zone 3.
With some reservation, I will include the yellow-foliage smokebush, Cotinus coggygria ‘Ancot' (aka Golden Spirit). The foliage is certainly quite beautiful and the leaves quite round; the fall colour is also an excellent orange. The problem is, it is rated for zone 5a so just barely makes it into the hardy shrub category. Even in my zone 5b, this one suffers from some die-back in winter.
Among the mockorange, Philadelphus coronarius, there is only one yellow-leaved variety, ‘Aureus', which is slightly more compact (1.5 -2.5 m) and smaller-leaved than the standard species. It has white, very fragrant flowers in early summer. This plant is also prone to leaf scorch in hot sites, so it is best to grow it in part-shade, where the late summer leaves will become more chartreuse. It is rated for zone 4.
Pictured above are Cornus alba 'Aurea', Cotinus coggygria 'Ancot' and Philadelphus coronarius 'Aureus'
Golden ninebark, Physocarpus opulifolius, is a popular landscape shrub across the Canadian prairies and US mid-west. The older yellow-leaved cultivar is ‘Luteus' which can reach 2-3 m. Much more popular is ‘Dart's Gold', a compact selection maturing at about 1.5 m. ‘Nugget' also matures around 1.5-2 m and has outstanding yellow spring foliage but matures to chartreuse. All of these produce rounded clusters of white flowers in late spring-early summer and appreciate some shade from hot afternoon sun in warm locations. They are very hardy, rated for zone 2.
Sumac, Rhus typhina, was not traditionally known for yellow foliage but recently has come the cultivar ‘Bailtiger', aka Tiger Eyes. Not only does this sumac have lovely golden foliage, it also has lacy, deeply-cut leaves and spectacular orange fall colour! It is not nearly as invasive or rambunctious as its green counterpart, topping at around 2 m. It is rated for zone 4.
Pictured above are Physocarpus opulifolius 'Dart's Gold' (full shrub and flower close-up) and Rhus typhina 'Tiger Eyes'
Elderberries have long been known for their yellow foliaged forms. The golden European or black elderberry, Sambucus nigra ‘Aurea', is all over my neck of the woods. It is a robust species reaching 3-5 m, although coppicing it will result in a smaller plant with huge leaves. Virtually identical is the golden American elder, S. americana ‘Aurea'. The main difference between these two is that S. nigra blooms 4-6 weeks earlier than S. americana. Both have flattish white flower clusters followed by small black fruit. The original yellow, cut-leaf form of red elderberry, S. racemosa, is quite attractive. It is called ‘Plumosa Aurea' and reaches 3-4 m, but like many yellow-leaved shrubs, is prone to sun scorching. ‘Sutherland Gold' is very similar but appears resistant to this problem. If size is a consideration, try ‘Golden Locks', a compact cultivar reaching only 100 cm. All the cultivars of S. racemosa bloom in mid-spring with globular creamy flowers followed by clusters of small, bright red berries. Elderberries, as a group, prefer evenly moist soil. All are rated for zone 4.
Above are Sambucus nigra 'Aurea' and S. racemosa 'Sutherland Gold'; please note that the foliage would be much more yellow if grown in full sun
The largest and perhaps most important group of yellow-foliaged shrubs are selections of Spiraea X bumalda or S. japonica. The first to arise was the very popular ‘Goldflame', a shrub whose leaves emerge orange-red and turn bright yellow as they mature. The abundant, flat-topped clusters of pinkish-red flowers over an extended blooming season is an added bonus. ‘Goldflame' is the tallest of the yellow spireas, reaching 1.2 m. The next to come along was the smaller cultivar ‘Goldmound'. The leaves are smaller and emerge more orange-yellow. It will reach about 80 cm. More recently, there has been a rash of new yellow cultivars including ‘Flaming Mound' (30-50 cm), 'Magic Carpet' (30-40 cm), ‘Candlelight' (60-90 cm), ‘Fire Light' (60-90 cm), ‘Lemon Princess' (45-60 cm), ‘Golden Princess' (60-90 cm), ‘Golden Elf' (25 cm) and ‘Mertyann' (aka Dakota Goldcharm) 35-45 cm. They are rated for zone 4 but if adequately mulched, they can survive zone 3, albeit, they may become more herbaceous in habit.
Shown above are Spiraea 'Goldflame', 'Gold Mound' and 'Magic Carpet'
There are no viburnums with truly yellow foliage, but two come close. Viburnum opulus ‘Aureum' and V. lantana ‘Aureum' both have leaves that emerge bright yellow in spring but by mid-summer mature to chartreuse . Both have white flowers followed by red and black berries respectively. They are both large shrubs reaching 3-4 m and rated for zone 3.
Last we come to Weigela florida. The most popular forms seem to be the variegated ones, but there are a couple of yellow-foliaged selections. ‘Rubidor' (aka ‘Olympiade') has brilliant yellow leaves with dark red flowers; quite a striking combination. It will reach 1.5 m. A new selection with pale cream-yellow foliage is ‘Ghost'. It also has red flowers. Both are rated for zone 4.
Shown above is Wiegela florida 'Rubidor'
In part 2, I will describe those hardier shrubs with red to purple foliage. Stay tuned!
I have many people to thnak for the use of their pictures: Gabrielle (Sambucus nigra 'Aurea' and Spiraea 'Magic Carpet'), irmaly (Sambucus racemosa 'Sutherland Gold'), bootandall (Physocarpus opulifolius 'Dart's Gold' flower), Equilibrium (Berberis thunbergii 'Gold Nugget'), GardenGuyKin (Berberis thunbergii 'Pow Wow'), jamie68 (Weigela florida 'Rubidor'), northgrass (Physocarpus opulifolius 'Dart's Gold'), victorgardener (Rhus typhina 'Tiger Eyes') and weebles64 (Spiraea 'Gold Mound')