Tuesday, February 9, 2021

Aralia cordata 'Sun King'

 Aralia cordata 'Sun King' has rocketed to stardom in the last several years and was named 2020 Perennial of the Year by the Perennial Plant Association. This wonderful plant was introduced by Barry Yinger of Asiatica Nursery, who brought it back from Japan. Barry brought a lot of great introductions into the country for the first time, often giving them appropriate names if their Japanese name wasn't valid. 'Sun King' was introduced to the wholesale trade by Terra Nova in 2011.

As a species, Aralia cordata is found in Japan, Korea, and eastern China. It grows to 6' or more (it's been reported over 8' in cultivation here in the states) and young shoots are cooked as a vegetable. It's the Asian counterpart to our native Aralia racemosa and is pretty similar. Both species inhabit similar niches in their range: woodland openings, woodland edges, and shaded areas of savannah. It's reportedly also closely related to another US native, Aralia hispida.

'Sun King' needs fairly good light to maintain a bright gold color. If it's in more shade it will turn chartreuse fairly quickly. So place it in bright shade, preferably with dappled light or even some direct morning sun.

'Sun King' will develop large compound panicles of white flowers, just like the plain green form of the species. Aralia flowers are generally very attractive to pollinators. Following the flowers, clusters of small black berries will form. None of my plants have done this yet, but I've always had to move away or move them before they've gotten fully mature! The berries pictured here are from a plain green A. cordata at Rotary Botanic Garden in Janesville, WI. 

It isn't a terribly picky or difficult to grow plant. I've had success with it in pots, in the garden in my silt loam here in z4, in clay-loam back in Sheboygan county, and in heavier clay soils in nursery display gardens. As long as it isn't too terribly wet or dry, it's easy to grow and worthy of its perennial of the year title. It does seem to best in fertile, well-drained soils, with some supplemental irrigation in summer. 

One of the most important things I need to stress about this plant is its mature size. Pretty much all of the commercial plant tags I've seen are incorrect, and online descriptions are often also misleading. Over and over I see this listed as growing only 3' tall x 3' wide. This plant will easily grow to 5' tall x 6' wide in 5-7 years, and larger over time. Barry's plant was certainly bigger than 3'x3' before the larger trade started growing it, judging by pics I've seen. So I'm not sure why this became the size everyone decided this would grow. A short 3 or 4 year trial maybe? I honestly don't know; but it's important to give this plant enough SPACE. Check out this specimen at Soule's Garden in Indianapolis eating its Hosta neighbors!

This is an excellent specimen or background plant for partial shade and it's easy to combine it with so many things. The compound foliage makes a good contrast with broad leaved plants like Hosta, Heuchera, Colocasia, Astilboides tabularis, Darmera peltata, Ligularia dentata, and a slew of others! The foliage is also bold enough to make a good foil for finer leaved plants like Iris, grasses and sedges, ferns, conifers, etc. 

I also think it's an excellent plant for a background to annuals and Rotary Botanic Garden made excellent use of it last time I visited. Don't be afraid to use it in beds with Coleus, or even in pots for a season and plant it in the garden at the end of the year. 

If you're not currently growing this in your shade garden, and you have the space, you really should add it. It's such a flexible plant and it's easy to grow. We'll be offering it again in the near future, probably available in late summer. 

Wednesday, February 3, 2021

Astilbe: A Horticultural Tragedy

Walk into any garden center and ask for perennial recommendations for shade. Likely the first thing to be recommended will be Hosta; the second thing will probably be Astilbe. If you're not familiar with Astilbe, they are perennials that provide essential early to mid-summer color for shaded gardens. And that summary is where our tragedy begins.

Shade tolerance is the start of our tragic tale. It's certainly true that Astilbe are shade tolerant. They're native mostly to Asia, with one species currently present here in North America, and are naturally found in forest edges, ravines, and other somewhat shady locales. Shade tolerance does not mean shade loving. They need bright light, preferably some direct sun, to perform their best. Given adequate moisture, they can even tolerate full sun in cooler climates. Placed in heavy shade they might grow fine, but are likely to bloom poorly, if at all, on less sturdy stems. Plants will likely be thin rather than dense. 

Adaptability is the next chapter of our tragedy. Most species of Astilbe are found in fairly moist habitats with rich organic soils. While they are somewhat adaptable to less wet environments and a range of soil types, they are not at all adaptable to dry gardens or clay soils. 

The best Astilbe I've seen were planted in an area that was receiving 2" of water per week from automated irrigation. They were lush and had hundreds of blooms on tall 40" tall stems; the best marketing images pale in comparison to these plants. The average homeowner, gardener, or landscaped business does not (and given future water availability concerns, probably should not) provide this amount of water. 

Most of us don't have ideal soil either; here in WI we mostly have heavy clay or sandy soils. Neither is ideal for Astilbe, which like organic rich soils. Fortunately, most shade tolerant plants also like organic rich soils, and if you plan ahead you can easily create raised areas to accommodate them. 

A special chapter of this tragedy goes to Astilbe chinensis, or if we use the currently correct name, Astilbe rubra. This chapter is titled: Drought Tolerance is a Lie. Astilbe rubra is found in equally moist habitats to other species. It tends to be more adaptable to average soils than other species, but this is NOT drought tolerance. Astilbe rubra and its cultivars and hybrids are probably the best choice for our gardens. They can go longer periods without irrigation than A. japonica or A. x arendsii cultivars and hybrids, but they will not survive actual drought conditions. In true drought conditions, plants can go weeks or even months without appreciable water. Many plants will survive drought conditions just fine. Astilbe, including A. rubra, will not. At the least they will go dormant and their health and vigor will likely be severely impacted  when moisture returns. 

Selection is the final chapter of our tragic tale. There are A LOT of Astilbe cultivars available. George Arends was instrumental in popularizing the genus, and introduced at least 74 cultivars over the span of 50 years. That quantity and pace has continued to this day. Just a quick browse of 4 wholesale suppliers turns up 70 cultivars. 17 of them are older cultivars but the bulk of the rest have been introduced in the last 25 years. 6 are new for introductions for 2021. A quick search of plant patents turns up 60 different patented cultivars. There is certainly room for a large pool of unique cultivars. But many of them are just incremental improvements over cultivars introduced prior to 1960. Slight differences in color, height, bloom count, etc. really bogs down consumers who are just looking for a great plant.  

The conclusion of this tragedy is that gardeners and homeowners are being set up to fail with a really fantastic plant. The horticulture industry needs to stop heavily recommending it to non-gardeners and beginning gardeners who are destined to fail because we don't educate them properly. The myth of drought tolerance needs to be dropped from our collective vocabulary in regards to this genus. At this point we need quality over quantity and inferior plants should be dropped from wholesale and retail offerings. To some extent this is happening; but probably not as much as needed. There also needs to be more extensive comparative trials in place, though the trend is for there to be fewer trials these days.

I love Astilbe, I intend to continue to expand the selection of cultivars we offer and trial varieties here in the garden to see which perform well for us and which can just fade into horticultural history. I'm even interested in breeding some more novel forms, but I don't know if I'll get around to that project. If you're struggling to grow Astilbe; water them more, maybe improve their soil if it's well-drained or heavy clay, move them into morning sun and afternoon shade or dappled light if they're growing in heavy shade. They will reward you with essential color in early to mid-summer. 

*a couple quick footnotes:

Astilbe crenatiloba is also a North American species, but it hasn't been found since the 1880s and is likely extinct or possibly just a variant of A. biternata

This post is absent of pictures because I've seen so few great looking Astilbe in the landscape that I've not managed to photograph them. When I *DO* see good ones it's not during bloom season!