Drought-Resistant Plants

By David Tarrant | Image: John Glover

Recent summers in this province have been particularly dry – last summer felt as if we were in southern California! Now, more than ever, gardeners want drought-tolerant plants, but in B.C., particularly on the coast, these plants must not only be able to withstand drought but also tolerate autumn and winter deluges of rain.

It is a fact that water is a precious commodity and should not be wasted on lawns and high-maintenance plant beds and borders. Fortunately, a wide range of lovely drought-tolerant plants is available to us, and by gradually changing our gardens over to such choices, we will lessen the heartache of loss while providing a pleasing and colourful landscape throughout the summer. Full sun and well-drained soil is absolutely necessary for all of them, well-drained soil being the key to their survival during those winter rains.

Allium cernuum, our native nodding onion, is indigenous to many areas of North America, particularly drier prairies and B.C. interior sub-alpine meadows. On hikes into the backcountry it is always a joy to find a clump or two of these wild onions – adding a few leaves to your sandwich can really spice things up.

The following plants are hardy to the zone number indicated: Allium cernuum (nodding onion) – zone 4 • Artemisia absinthium ‘Lambrook Giant’ – zone 4 • Artemisia alba ‘Canascens’ – zone 4 • Crocosmia ‘Lucifer’ – zone 6 • Hieracium lanatum – zone 5 • Lychnis chalcedonica (Maltese cross) – zone 4 • Lychnis coronaria (rose campion) – zone 4 • Penstemon heterophyllus – zone 7 • Phygelius x rectus ‘African Queen’ – zone 8 • Salvia officinalis – zone 5 • Salvia sclarea (clary sage) – zone 5 • Thymus pseudolanuginosus (woolly thyme) – zone 4 • Yucca glauca – zone 3 • Yucca filamentosa ‘Golden Sword’ – zone 5

In the wild this is a rather low-growing bulbous perennial with strap-like leaves. During summer stiff stems 30 to 60 cm (1 to 2 ft.) in height with sharply curving tips bear pendant umbels of 20 to 40 bell-shaped pink flowers. In a cultivated garden situation, the taller stems are the norm. It must be stressed that these nodding onions need really well-drained soil. You can see a large patch at the entrance to the Native Garden at UBC Botanical Garden where, for more than 10 years now, every summer their massed flowers look like a pink mist for six weeks. After they have finished blooming, the attractive seed heads remain all summer long. In the right conditions they seed themselves about, not to the point where they become weedy, but just enough to maintain the quality of their planting area. They are very hardy, to zone 4.

While I do not have a garden of my own, if I did I would interplant my nodding onions with Artemisia alba ‘Canascens,’ a clump-forming semi-evergreen perennial with intricately formed silver leaves. The pink haze of the nodding onions combines with the laciness of the artemisia to conjure up a very pleasing and relaxing effect. While artemisia’s flowers are brownish and not terribly attractive, its lovely foliage forms a rather nice clump with an overall height of about 20 cm (4 in.). Hardy to zone 4 and up, this one prefers a dry, sunny and well-drained spot. It seems quite deer-resistant, too. For those wanting to make a stronger statement, Artemisia absinthium offers the same exquisite foliage in a 75-cm (30-in.) version.

Silver foliage is usually a dead giveaway that a plant is from a dry region of the globe and therefore ideal for drought-prone garden spots. This next one, Hieracium lanatum, may be more difficult to find and is a little less hardy – to zone 5 and up. It is native to southern Europe.

This is a clump-forming perennial with attractive, lance-shaped, grey-green and white-margined leaves up to 10 cm (4 in.) in length. They are densely clothed with long white hairs, which give them their distinctive colour. Each leaf is somewhat cupped, making it even more intriguing. In summer, wiry branching stems up to 45 cm (1 1⁄2 ft.) long bear loose panicles of deep-yellow flower heads. Some people want only the silver effect of the foliage and remove the flower stems as they appear, but in the right location and grown in large clumps, the flowers can really brighten up a border. Poor but well-drained soil is the key to success with this one.

Silver-foliaged Thymus pseudolanuginosus, fondly known as woolly thyme, is a mat-forming sub-shrub native to Europe and hardy to zone 4. Its tiny oval leaves are covered with minuscule silver hairs that give the plant its common name. In midsummer whorls of very small pink flowers are produced. In Europe, woolly thyme has long been used to fill in the cracks of flagstone paths or cover dry-stone walls. In fact, at Sissinghurst in Britain and at Ravenhill Herb Farm on Vancouver Island, there are attractive stone benches planted with woolly thyme to form cushions on the seat; as one sits the aroma of the thyme is released into the air.

I find this little plant to be great all season in the dry interior, the Gulf Islands and in arid spots in the garden, however on the soggy coast it has been known to turn black in the winter. Don’t be discouraged, though – it does bounce back in the early spring. In dry areas, it can even serve as an alternative to a small grass lawn if it doesn’t get too much foot traffic, as thyme will stand up to some, but not constant foot traffic. It is great for boulevard planting, and if interplanted with strong foliage plants such as Yucca glauca or Yucca filamentosa ‘Golden Sword,’ it can create a very pleasing textured planting.