Too much moisture, too little, and just right


The dwarf crested iris (Iris cristata ‘Tennessee White’, below) is a vigorously spreading native to woodlands and along streams in the eastern and southeastern United States, so the gardener would suspect that it grows best with abundant moisture, and perhaps some shade. But, the iris grows best in nearly full sun, and I’m afraid that I’ve surpassed its tolerance for soil dampness. In the prolonged rainfall in September last year the soil in the lower garden remained saturated for a month or longer, and I was afraid that ‘Tennessee White’ had disappeared.

For a few years the low growing iris clump doubled in size annually, but by October last year the foliage had faded, and I feared that it had rotted in the wet soil. There was no sign of the iris until a few weeks ago, and now the clump has diminished substantially. There was one flower, but I’m happy at least that it survived, and I don’t figure that we’ll have another September with twelve inches of rain to worry about for awhile.

The flowers of ‘Tennessee White’ are supposed to persist longer than other dwarf crested irises, but this single bloom only stayed around for a few days, so it was disappointing. If there was another spot that had ideal conditions for the iris I would move it, but there are few areas with enough sun to please it, so I’ll take my chances on leaving it where it is. Sometimes a plant is left in unfavorable conditions to eventually perish because it is too much work to move it, but the tiny irises would be scooped up with a single swipe of the trowel.

In nearby soil that is waterlogged through much of the year the clump of Spanish bluebells (Hyacinthoides hispanica, above) merrily increases in size each year. This spring has been quite dry, but the bulbs sprouted and flowered without a care in shallow standing water in last year’s wet early spring. I’ve read that they can be a bit invasive in damp conditions, but I’d be happy if they were to spread far beyond the small patch where they are now. There’s a hundred feet of low lying, wet ground to cover before the back end of the garden, and the bluebells are welcome to cover every inch before I’ll be concerned about them being too invasive.

I occasionally read that bugleweed (Ajuga reptans ‘Chocolate Chip’, above) can become too aggressive, but I’ve had trouble with it surviving, probably because I’ve tried to push it into dry shade when it prefers more moisture. A few years ago I planted a variegated leaf bugleweed in the shade of the large purple leafed beech in the front garden, but it didn’t survive the year, even with soil that was heavily amended with compost. Under the beech the soil remained dry, no matter how much compost was worked in. Now, I’ve planted the small purple leafed ‘Chocolate Chip’ across the stone path, only a few feet away, and with a bit of sun, and less competition from roots to rob moisture, the bugleweed is content and spreading quickly. If it grows well enough to be just a bit of a problem, I’ll be satisfied since it’s a wonderfully colorful groundcover with superb blooms in April.

I’ve discovered countless times that native plants are just as likely as any other plant to fail if planted in the wrong conditions, and I’m happy to report that I’ve finally succeeded with large-flower bellwort (Uvularia grandiflora, above) after a few failed tries. In the past I think it’s been too dry, and then too wet, but the latest plants have settled in for a third spring now, so I think the bellworts are here to stay. The spot is a little shadier than I’d like, so perhaps they won’t grow as quickly as I’d prefer, but I’m not arguing with success. Bellworts are susceptible to grazing by deer, but I’ve planted them alongside a small bluestone that is bordered by hostas and hellebores, and the deer seem reluctant to walk on the slick stone surface so I don’t have to spray a repellent in this area.

I don’t know that spurges (Euphorbia) as a whole prefer bone dry ground, but whenever I’ve failed with them the soil was slightly damp, though not close to what I would consider wet. There are numerous varieties available, and in dry shade or sun they flourish in my garden. The fifteen inch tall Robb’s spurge (Euphorbia amygdaloides var. robbiae, above) spreads vigorously through root infested shade beneath tall maples and tulip poplars, though it is easily controlled when it pops up through the stone path. I don’t know how the rhizomes can pass under and around the large roots that prevent me from planting anything else in this area, but I’m happy to fill the space with such a long blooming and carefree perennial.

In full sun at the other end of the garden threadleaf spurge (Euphorbia cyparissias, above) meanders contentedly through granite boulders and river gravel that border the large swimming pond. This spurge can be quite aggressive (I’ve read), but here it is bordered by larger evergreens and a stone patio that keep it within bounds. In late March through April the yellow flowers contrast nicely with slightly reddish foliage, and even when the blooms fade the foliage is effective through the heat of summer.

Beside the spurge in the dry shade variegated Solomon’s Seal (Polygonatum falcatum ‘Variegatum’, below) has spread slowly into a nice clump. By mid April the arching stems are lined with tiny white bells for a few weeks, and then the white striped foliage looks fresh through the driest periods of the summer. I don’t know how Solomon’s Seal would fare if given more favorable soil and a bit more moisture, but in dry shade it performs admirably. 

2 Comments Add yours

  1. Eric says:

    Euphorbia and Polygonatum are among my absolute favorite perennials. They give so much and ask for so little in return…

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