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?