WASHINGTON -- Perennials all come up from their roots spring after spring, but some are better performers than others. Many fall-blooming mums and even some fancy black-eyed Susans degenerate after a few years into weedy clumps with stunted flowers. The faithful perennials are the ones that not only show up unfailingly but look just as lovely as they did the year you first planted them.
You will still need to lift and divide them after several seasons.
An early-summer bloomer, Siberian iris is a good plant to take over after daffodils and other spring-flowering bulbs are spent. The best colors are the strong blues and yellows of other irises, and the size and beauty of the blooms do not decline over time.
Thriving in the shade, astilbes have similar characteristics. Their vigorous, fernlike foliage soon covers the ground. Hybridizers have been busy working on astilbe flowers, developing a surprising diversity in feathery plumes, some dense and others ethereal, but all as symmetrical as a traditional Christmas tree.
The color spectrum is limited to the one between white and a dark red, with scarlet and peach perhaps the most dramatic.
Astilbes have to be divided every three or four years, in early spring or early-to-mid-fall. Astilbes mixed in with hostas look good together and extend the flowering period in the shade.
Hostas are not for those gardens visited by deer, voles, moles or slugs. Apart from those pests, hostas are indestructible. They double in size in most years and should be divided every four years or so. The best instruments are a serrated kitchen knife and a sharp straight-edge spade. The cut can be along straight lines, regardless of the ''eyes'' that are damaged in the process.
One admirable faithful perennial that does not need to be divided is the globe thistle (Echinops retro). A fairly recent addition to the American garden, globe thistle is fairly tolerant of drought and will make do in average soil if it is porous. Its spiny, thistlelike leaves contrast with the perfectly round flower heads. The champion cultivars are Veitch's Blue and Taplow Blue, both true-blue blooms that look heavy yet do not keel over in storms. If deadheaded, they will come back through most of the summer. The blooms make fine cut flowers and also are a sturdy addition to dried-flower arrangements.
The perennials mentioned here require little maintenance. Planted in reasonably good soil -- and it pays to put them in a bed well-supplied with organic content -- they provide a steady performance and deserve our loyalty.
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