Does lasting beauty exist outside of Hollywood? Yes, it could be in your garden! And if you’re tidying up borders before taking off for warmer climates, or perhaps just snoozing through autumn – are you sure that garden growth is really finished for this year? Think again. It’s autumn. Tree leaves are turning colour, perennial plants are dying down and the season is ready to close with the first light frost. Or so it would seem. But there is a category of plants that are still in expansive, spreading mode and ready tomake landscape gains fromOctober throughmid-December. Plants with underground rhizomes and aggressive root systems are invigorated in cool temperatures and make significant growth that won’t show above ground until next spring. Light frost only encourages them and it takes a deep, penetrating frost to shut themdown. But turn your back on themnow and they’ll be in your face next spring. Rhizomes are modified stems running horizontally underground at shallow, six- to 10-inch levels. You have probably encountered a rhizome when weeding or digging a planting hole; it’s a horizontal, swollen, stem-like structure connected to thinner horizontal roots at each end, with fine hairy roots growing downward. Rhizomes are powerhouses of reproductive activity that store energy and direct growth. They are very effective at spreading plants across garden spaces during the spring growth bonanza and again in autumn, and will out-compete more refined, less vigorous root systems. What are these plants with such thuggish roots? Some are notorious weeds which we know to remove, such as creeping Charlie, horse tail, stinging nettle, Japanese knotweed and poison ivy. However, others are such familiar perennial plants as bugleweed (ajuga reptans), bellflowers (Campanula rapunculoides) Chinese lanterns (Physalis alkekengi), bunchberry (Cornus canadensis), interrupted fern (Osmunda claytoniana), plume poppy (Macleya cordata) and yellow archangel (Lamium galeobdolon). These ornamental spreading plants are an asset when you want to fill bare space, but their vigour might need to be controlled when they’re given luxurious living conditions in garden beds. What to do about this? Research groundcover plants before purchasing them, whether they have simple root systems, or include rhizomes in their underground structure. Not all are invasive, such as day lilies and irises that grow fromnon-aggressive rhizomes. Use spreading ground covers wisely, installing them as landscape cover where you have bare and open space to fill. They will do this well and make you happy; but give them their own area and avoid putting them into garden beds where they can swiftly overwhelm less vigorous perennial neighbours. Vigilance is the key to keeping useful spreading plants contained in their areas. At end of summer, check to see how much growth they’ve accomplished. If ground-cover plants have abutted their edges with lawns or other ornamental plantings, that’s the sign that they will be invading next spring with underground roots and rhizomes. Set them back in autumn by digging a clear six- to 12-inch (30 cm) division between areas, removing roots and rhizomes which you may uncover. This will be the stop gap that brings peace of mind when you settle down under a warm sun this winter. Gardening by Judith Adam Rhizomes in cold climates Darwin tulip 50 | www.snowbirds.org
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