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Eugene Weekly : Gardening : 5.10.07

Heuchera Heaven

Colorful plants love pots


Now why didn't I think of that? I opened a British gardening book the other day and saw a mass of chocolate cosmos growing in a pot. Chocolate cosmos is a great candidate for container culture: It is slightly tender, a bit of a specialty and not always easy to grow. I have killed more chocolate cosmos than I care to remember. My guess is, it's a plant that likes what Brits call "a warm, light soil," something I definitely don't have. In a pot, I could give it the conditions it prefers and keep it nearby, the better to enjoy its peculiar fragrance and subtle coloring.

Pot culture is ideal for other plants, of course. Heuchera, for example. Old fashioned garden coralbells, useful for filling in a border edge, had more or less green leaves and showy red or pink flowers. The flowers of many new heuchera varieties are pretty forgettable. Foliage is the point, and we are offered a torrent of pricey plants with wildly colorful leaves. If you can afford them, they are irresistible, but they can also be maddeningly short-lived in gardens. All the ones I have tried, however, have something in common: They are far happier in pots than in my rather dense, moisture-retentive garden soil.

For years I thought heucheras needed lots of moisture, but books said otherwise. I finally figured out that the plants in my garden had poorly developed shallow root systems, and that's why they threatened to poop out in hot weather. As pot plants they are, in fact, reasonably drought tolerant, and like so many plants that prefer exceptional drainage, they also grow better in pots. If you have the sort of garden soil you can plunge a hand into to pull a weed out by the roots, heucheras will no doubt love your garden. Otherwise you may be better off planting them in a rock garden or raised bed, or in containers.

Heuchera heaven is probably a well-watered pot with a bit of shade in the afternoon, but some varieties perform very well in less than perfect conditions. The toughest make a reasonable showing in my best garden soil, though no amount of coddling can produce in the ground the results I get in pots. Well-grown heucheras, most of them, revel in sun, flowering freely on long, strong stems and developing their finest foliage color. In varieties with chartreuse, yellow or orange coloring, however, partial shade brings out the best color in the leaves.

The old stand-by 'Palace Purple' (the plant that started all this foliage color stuff) is also better in light shade, where it makes a great container plant. Shop around for specimens with no green or olive cast to the leaves. A good clone has heavily textured leaves, glossy when new, dark maroon on top and reddish purple underneath. (I saw some good ones recently at Fox Hollow Creek Nursery, 28th and Friendly, off the Dari Mart parking lot.) 'Palace Purple' is more evergreen than most heuchs. Its performance in cold weather pots is outdone only by Heuchera americana 'Dale's Strain,' with green, red and pewter leaves that darken dramatically in winter.

Newer foliage colors can be quite amazing. 'Lime Rickey,' 'Marmalade' and 'Frosted Violet' — the names speak for themselves. In the garden, I choose proven performers in slightly less eye-catching shades: 'Mint Frost,' 'Plum Pudding,' 'Pewter Veil' and 'Green Spice' are all strong growers. Given suitable soil, heucheras are relatively trouble free. Root weevil larvae sometimes chew off the roots. The top growth can be rescued, if you find it in time, by embedding the pieces in new soil. Heucheras benefit from frequent division in any case, and it's easy: From late winter through early spring, cut off elongated stems, trim off the lower leaves and plant the stems in fresh soil amended with a little all-purpose organic fertilizer, one that contains lime. You will have new plants in no time.

The entire genus Heuchera and several close relatives are native to North America, most of them here in the West. Small-flowered alum root (Heuchera micrantha, a parent of 'Palace Purple') is found in rocky places in the Willamette Valley and the surrounding mountains. Fringecup (Tellima grandiflora) is almost ubiquitous in some gardens, an obliging placeholder for finer things to come and a nice plant in itself. Tiarella, a local forest genus, has been hybridized almost as busily as heuchera, producing some charming, colorful small plants for moist, shady gardens. Fancy tiarellas (and the intergeneric hybrid, heucherella) are useful container accents for shade.   

Rachel Foster of Eugene is a garden consultant and author of All About Gardens, a selection of past Eugene Weekly columns. She can be reached at rfoster@efn.org