Friday, December 24, 2021

Tiarella - Foam Flower

Tiarella is a genus of woodland perennials found mostly in North America, with one species currently known from Asia. Closely related to Heuchera, the two genera can be hybridized to create the sterile intergeneric hybrid xHeucherella. 

Taxonomic work is still ongoing, with different authorities having drastically differing species listings. World Flora Online lists T. californica, T. cordifolia, T. laciniata, T. macrophylla, T. polyphylla, T. trifoliata, T. trifoliata var. laciniata, T. unifoliata, and T. wherryi as accepted names. The glaring problem with this list is that T. trifoliata var. laciniata and T. laciniata are the same plant! The USDA database lists T. cordifolia var. austrina, T. cordifolia var. collina (synonym for T. wherryi), T. cordifolia var. cordifolia (syn. T. macrophylla), T. trifoliata var. laciniata (syn. T. laciniata and T. californica), T. trifoliata var. trifoliata, and T. trifoliata var. unifoliata. These varieties are separated by questionable morphology that doesn't seem to hold up across their range, there is definitely overlap. T. polyphylla seems to be the only species with not much controversy about its taxonomic status, though I'd be unsurprised if other species were discovered in Asia. Confused yet? That's ok, so is everyone else! 

Fortunately, as gardeners, we're dealing primarily with hybrids. Or if you're a native plant nerd, you're probably dealing with more local sources and a deep dive into taxonomy isn't really necessary; you just need to know how close to home your plants originated. 

Tiarella mass planting at Chicago Botanic Garden

Tiarella grows in bright wooded edges and clearings and fills that niche in gardens as well. Organic rich soils in bright shade or morning sun with dappled light the rest of the day is ideal. As a mass planting with other native woodland species or non-native shade lovers, Tiarella makes a huge impact. If used with ephemerals, the foliage fills in the space left behind after ephemerals go dormant. It blends well with crested Iris or woodland Phlox as well as larger Hostas. 

Pollinators really like Tiarella and it's visited by bees, syrphid flies, butterflies, moths, and hummingbirds. Not too much feeds on the foliage, slugs being maybe the worst offender, but damage from them is pretty minimal in the gardens here. Rabbits and deer mostly leave them alone, but will feed on the evergreen foliage in winter if it's not snow covered. 

There have been a lot of cultivars introduced over the last 25 years or so. I wouldn't say any are specifically bad and you can easily pick a popular, readily available cultivar and be satisfied with it. It's also easy to pick several varieties for different applications based on growth habit, foliage form, and foliage color. 

I am growing 'Sugar and Spice' in full sun right now and it's been quite vigorous with the additional light and water, but I don't recommend this for most people. I had to water a LOT with this year's drought; I only have it planted in its location because in a few seasons it will be more shady once the shrubs fill in and I don't want to renovate. It's close to my hose and a high traffic area, so it's easy to give it extra attention. My friend Larry Conrad uses this variety exclusively in his gardens planted with Trillium and Phlox divaricata. This is a good example that if you only grow one variety you'll probably be happy with it, regardless which it is. 

Tiarella 'Sugar and Spice'

Tiarella 'Brandywine' in early spring

'Brandywine' is a broadleaf hybrid of T. cordifolia and I was impressed with the heavy bud set I saw in potted plants just emerging from dormancy several years ago. The foliage still had burgundy and bronze tones from winter. I like blending this variety with finer foliage textures. If you want a Tiarella to blend with ferns or sedges, this is a good option for texture contrast. 

Tiarella 'Spring Symphony'

Tiarella 'Spring Symphony'

'Spring Symphony' is an older favorite of mine. It offers a heavy bloom show well distributed over the plant, deeply lobed foliage, and decent growth. Like I talked about with 'Sugar and Spice', I don't think this is any better than other varieties and you could easily grow 'Pink Skyrocket', 'Cutting Edge', 'Gowing' ANGEL WINGS, or any number of others and be just as happy with them. 

Tiarella 'Susquehanna'

Tiarella 'Susquehanna'

'Susquehanna' is another one that I've had around for awhile. It's another T. cordifolia hybrid like 'Brandywine', but with smaller foliage that's a little more lobed and is slightly rhizomatous. It's grown well in its new location and gave me a great flower show this spring. Flowers lasted a fairly long time as well.  

I don't have my own pictures yet and I don't like to use promotional pictures, but I need to at least mention 'Pink Skyrocket' since it's been incredibly popular for a long time. It has deeply lobed leaves like 'Spring Symphony' but the lobes are broader and coarser. Pink buds open to flowers that are blush pink to white. Fall and winter color ranges from orange to bronze. Despite being introduced 20 years ago, it's still one of the top selling varieties overall and one of the best for pink flowers. A new variety, 'Gowing' ANGEL WINGS looks like it might be very similar but with finer-textured leaves and I'm excited to compare the two varieties in 2022. 

Friday, December 10, 2021

Native groundcovers for shade.

I often get asked about groundcovers for shade. There are certainly a lot of choices out there; and while I like plenty of non-native selections, I find myself gravitating more and more to native species and selections of them. Not all of them are suitable for every garden, some definitely want specific conditions to perform well and some are only suited to special uses. 

A group that is becoming more and more popular are the sedges of the genus Carex. This is a huge group of plants and not all are great garden plants, but that's ok because we have A LOT to choose from! Just here in Wisconsin we have 167 species and naturally occurring hybrids! 

Carex muskingumensis 'Little Midge' is a dwarf selection of a native species that's usually found in wet areas. Despite this habitat preference I've found the species is suited to average moisture conditions. One of the common names of this species is palm sedge, for it's upright whorled stems of foliage. 'Little Midge' is great because it's a very petite form that only grows to be 6" tall or so. I grow a variegated form, 'Oehme', that grows to be about 12" tall. It's a nice accent plant, but it's a bit big for groundcover duty with other perennials. 

Carex platyphylla is a broad-leaved sedge with silvery foliage. This species forms loose colonies that intermingle with other plants well. Foliage is evergreen and can be cleaned up in spring. It's very low, generally only to 6" tall with flowering stems that may reach 10". But flowering is loose (first picture above) and airy and is over quickly. I really like blending the broad-leaf sedges with finer textures like ferns or even dwarf conifers. There's even enough texture contrast to blend with finer leaved sedges as well. 

Carex pensylvanica is likely the most common sedge in Wisconsin woodlands; certainly the one I've encountered most often anyway. It forms large, loose colonies and has a very wispy natural turf kind of look; very soft and inviting. It plays very well with other robust perennials, pictured above in spring with Jacob's ladder, Polemonium 'Heaven Scent'. I only know of one selection, 'Straw Hat', with flowers that are larger than normal. It does great in average garden conditions. 

Carex appalachica, Appalachian sedge, isn't native here in Wisconsin but is found in eastern North America. It looks like a smaller and finer version of C. pensylvanica, but tends to stay put rather than spread. In spring and as young plants it's very upright as pictured here, but foliage can grow to 10" long and weep over. It's great with Hosta, Heuchera, Brunnera, and other broad textures. 

Another great native groundcover, pictured above with Carex appalachica, is wild ginger, Asarum canadense. It's best used with more robust perennials or under woody shrubs as it can form fairly dense colonies. It is great for use as living mulch under woody shrubs as it's fairly drought tolerant. 

Clintonia borealis, or blue-bead lily, is common here in northern Wisconsin but seen less often in Southern Wisconsin in my experience. When not in flower it resembles the non-native lily of the valley. Clusters of yellow lily-like flowers (it's in Liliaceae) in spring are followed by blue berries, hence the name blue-bead lily. It likes organic rich soils with even moisture. If happy it can form fairly dense colonies, but it's not aggressive. You can easily pair it with other perennials. 

Chamaepericlymenum canadens (formerly Cornus canadensis) or bunchberry is only suited to well-drained acid soils. It's prevalent here in the north and can be found growing in similar conditions to blueberries. If you can provide good conditions for it, it forms loose colonies of whorled foliage with impressed veins, topped with white dogwood flowers in spring and followed by red berries. 

Virginia waterleaf, Hydrophyllum virginicum, is a very lovely plant in spring. Foliage is marked with silvery splotches, resembling watermarks. Later in the season the foliage is solid green. Clusters of lavender flowers top the foliage in spring and are great for pollinators. This is a very aggressive plant and will seed around with abandon. It roots in well and is difficult to pull. I don't find it suited to average gardens. But if you need a groundcover for under woody plants where you're not going to grow other perennials, it works well. It's also great in natural areas and is worth adding for pollinator use if it's not present in your woodland; woodland spring ephemerals grow with it just fine. 

There are a lot of really neat woodland Iris species available, several from Asia; but in the US we have Iris cristata which is a lovely diminutive woodland species. There are many cultivars available, pictured above is 'Edgar Anderson'. The most commonly available ones are the species, 'Powder Blue Giant' (with large pale lavender-blue flowers) and ' Tennessee White' with larger than average white flowers. On the shores of Lakes Michigan and Huron, we have the closely related Iris lacustris, which is a federally threatened species. It grows in sandy, calcareous habitats on the Niagara escarpment. Habitat loss threatens this species. (If anyone has specimens propagated by license, please contact me!)

Linnaea borealis, twinflower, is present throughout Wisconsin but I've seen it more often here in the north than I did when I lived in southern Wisconsin. It forms very low, loose carpets, of small foliage topped with pairs of flowers ranging from white to very pale pink. It seems to like well-drained but organic rich soils. I expect it should perform well with plants as small as miniature Hosta; I'll let you know how that goes! This plant used to be the sole member of the genus, but recently several other genera like Abelia and Kolkwitzia have been merged into it based on DNA evidence. We'll see if this lasts or gets changed again in the future. 

Mitchella repens, partridge berry, is a very petite denizen of deciduous forests from Texas east to Florida and north to Ontario and Quebec. Plants are generally just a couple inches tall here in Wisconsin and found in mesic forests that don't get too terribly dry. Some people have struggled to grow this in gardens and others have succeeded just fine. I picked up a bunch in spring but life kind of got in the way of getting them planted. So if they overwinter alright I'll get them planted in spring. If not, I guess I'll order more! I need to figure out how all of you can grow them, because it's delightful!

Allegheny spurge, Pacysandra procumbens, is our native Pachysandra found from Kentucky to Mississippi and South Carolina. It's actually fairly cold-hardy and can be grown to at least zone 5. Foliage is evergreen and often marked with silvery green and burgundy in cool weather. In spring, white bottlebrush spikes of flowers emerge. This plant is larger and a bit more coarse than the Asian species usually used en masse here, but it's absolutely beautiful and worth considering. I'm trialing several plants here in the north, hoping our snow cover allows it to survive!

Phlox stolonifera might be my favorite native groundcover. It's found from southern Maine to Ohio and south to Georgia. It forms dense mats that weave around other perennials beautifully. In spring, these mats are topped with flowers on stems to 10" tall in a range of colors from white to pink or purple. 'Sherwood Purple' is probably the most mildew resistant variety that's readily available. Other varieties like 'Pink Ridge', 'Home Fires', and 'Fran's Purple' are less common but equally excellent. Powdery mildew hasn't been an issue at all for me here, but it can be an issue in other parts of the country. Good air circulation and even moisture during drought can help reduce mildew infection. 

Bloodroot, Sanguinaria canadense is a lovely spring blooming plant with short-lived white flowers and interesting lobed foliage. It's probably best used with larger woody plants or in natural settings, or use the sterile cultivar 'Multiplex'. As you can see in the second picture, seedlings have grown in so dense that they're outcompeting Lamium and a large Hosta cultivar and managed to choke out the struggling Brunnera macrophylla 'Jack Frost' and Dicentra spectablis 'Gold Heart' shortly after this picture was taken. But in the right spot it's delightful. The seedlings in bloom in the top picture are competing with the equally weedy Allium 'Purple Sensation'. 

Tiarella are popular plants, mostly represented in the trade by hybrids like the mass planting pictured above. But the species are obtainable and make excellent garden plants. Here in the eastern US, the genus is represented by T. cordifolia and its 3 subspecies with it's more broad, round-lobed foliage. The western US has another species, T. trifoliata also having 3 subspecies. (Some authors elevate some subspecies to species level, work is ongoing on their taxonomy) Many hybrids also have genes from the Asian T. polyphylla. Most forms are clump-forming with a similar habit to the closely related Heuchera, but running forms of T. cordifolia exist as well and make great spreading groundcovers that weave around other plants. 

VIOLETS? Yes. Violets. Native violets are underused and too often considered weeds. Yes, most will seed about. But they're important plants for pollinators and certain butterfly and moth species. The yellow Viola pubescens is present in mass quantities in my lawn here. As I expand those areas into gardens, I move some to open shaded natural areas. The purple V. adunca and white V. renifolia pictured above are fairly petite species, and even if they would seed around aggressively, are small enough to play well with most perennials. If you  have an area of shade from maple trees and can't grow a typical turf but don't want a garden area, how about Carex pensylvanica and violets? It would be green, require practically no mowing, and provide habitat for many beneficial insects which provide food for songbirds and other animals.

There are obviously many more native groundcovers for shade, I've just touched on a few that are good for different uses or are popular. I'm sure I'll talk about some more in the future. I didn't really cover many ephemerals which make good temporary early season groundcovers or larger groundcovers. What have you done well with? What plants are you curious about? 

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! 

Tuesday, January 19, 2021

Hybrid Echinacea

14 years ago Echinacea ‘Art’s Pride’ ORANGE MEADOWBRITE arrived on the market and the world of coneflowers was changed forever. This hybrid of E. purpurea ‘Alba’ and E. paradoxa opened the floodgates of hybridizing this genus of stalwart garden plants. Soon hybrids from Richard Saul and Terra Nova nursery started hitting the market.
‘Sunrise’ from Richard Saul

‘Tomato Soup’ from Terra Nova

But these colorful new hybrids weren’t without their problems. Many gardeners had trouble keeping them alive, especially in areas with heavy soil and wet winters. This has a lot to do with E. paradoxa being found primarily on very well-drained soils rather than a lack of hardiness.

Large clumps of ‘Sunbird’ (left) and ‘Flame Thrower’ (center) with E. purpurea ‘Showoff’ (on the far right) 

Subsequent years of further hybridizing have made the newer hybrids a little easier to grow, but they still do best in well-drained soils. Provide proper drainage and they will get just as large as, or even larger than, old fashioned E. purpurea.

The best performers for me have been ‘Firebird’, ‘Sunbird’, and ‘Flame Thrower’ from Terra Nova nurseries. These are 4th generation hybrids bred from E. paradoxa and E. purpurea ‘Ruby Giant’.They’ve done very well in several gardens for me, with the ‘Flame Thrower’ pictured above at 7 years old.


‘Flame Thrower’


‘Flame Thrower’

I’ve also had fairly good luck with the Sombrero series from Ball. This is a compact series with plants reaching 18-24″ in height and several varieties in shades of orange, red, and yellow are available.
Sombrero mix

Sombrero ‘Salsa Red’

Sombrero ‘Tres Amigos’

If you’ve tried some of these fantastic plants before but struggled with them, don’t be afraid to give them another try. Improve your drainage by creating a raised bed or planting on a slope. Use aged pine bark or pumice as a soil amendment to increase porosity and improve drainage. Visit public gardens and see which varieties are doing well in your area. Don’t be afraid to fail and try again or try new varieties. Experimentation is part of the fun of gardening.