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Ask the Gardener: Lily of the valley launches a hostile takeover

Ask the Expert Gardening
Lily of the valley is a garden thug. Getty Images

What to do this week: Take time to smell the unfurling peonies and roses. Finish planting cold-sensitive flowers such as impatiens and dahlias, as well as warm-weather vegetables such as tomatoes, beans, melons, squash, corn, peppers, pumpkins, cucumbers, and eggplant. Consider pots of culinary herbs such as basil, rosemary, chives, oregano, parsley, sage, or thyme for a sunny outdoor spot near the kitchen door. They are easy and give a big bang for the buck if you cook, and who doesn’t these days? When planting container gardens, remember that the larger the pot, the less frequently you’ll need to water it. Consider buying a “self-watering’’ outdoor container.

Q. I have a rock garden to the side of a small pond with perennials like bleeding heart. In my haste to get more coverage, I planted lily of the valley. It’s taking over and growing in the ginger with waxy leaves that I love. Will it take over my ginger? Do I pull it out?

B.P., Reading

A. Sooner or later most gardeners learn the sad lesson that even a pretty plant can be TOO vigorous. Though lily of the valley is delicate-looking, the surprise is that it’s a real garden thug that does not play well with others. So, yes, pull out all of its tenacious little creeping rootstalks. You may have to dig up the plants it has already infiltrated like your European ginger and either disentangle the roots or discard the whole mess. And if you give any lily of the valley away, do warn your recipient to isolate it in a shady spot where they can safely harvest the beloved scented white bells for nosegays in May without it overwhelming their other plants. Many perennials once hailed as low-maintenance ground covers have turned out to be relentless invasives. Avoid planting periwinkle (vinca minor), ribbon grass (phalaris arundinacea), wintercreeper (euonymus fortunei), English ivy (hedera helix), or any plant described as a “vigorous spreader,’’ which is nursery code for “unbridled aggressor.’’ Choose the perennials you add to your garden beds of horticultural treasures as carefully as you would pick playmates for your children. Ban the bullies!

Q. I have gorgeous bearded iris in a rock garden. The upper level has stopped blooming. They are in full sun with healthy foliage, and I added compost. What happened?

R.S., Sudbury

A. Bearded iris is indeed a gorgeous perennial for full sun. Thanks to devoted breeders, it comes in many sizes and fascinating color combinations, but the flowers stop blooming when the roots become overcrowded. So about every five years there comes a summer day when you need to grab a large garden fork and pry the shallow, fleshy iris rhizomes out of the ground. Cut or pull these apart, leaving about three fans of leaves attached to each piece. Replenish their bed by digging in compost before replanting the divided rhizomes horizontally and just barely covering them with soil. Water them deeply to firm the soil (no stomping), and then cut the leaves back by two-thirds. You can give leftover plants to other gardeners or trade varieties with them to build your collection. If you want to really explore the seductive world of irises, visit the excellent Massachusetts Iris Society at massirises.org for local sources and events.

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