What to do this week: Cut or pinch spent phlox flower heads to encourage rebloom and prevent inferior seedlings from sprouting and crowding out their prettier parents. Pinch off the tops of tomato and Brussels sprout plants to hasten ripening. Plant more arugula. Place mail orders for fall bulbs, and when they arrive, stick them in when you are planting new perennials. For more cutting flowers in next summer’s garden, add balloon-flower, helenium, garden phlox, rudbeckia, Shasta daisy, coneflower, and perennial sunflowers. If deer are a problem, plant astilbe, bleeding heart, salvia, peonies, globe thistle, perovskia, “Roxanne’’ perennial geranium, grapeleaf anemone, and aster. Cut back unsightly old foliage from early bloomers to give the garden a refreshed look. This is the best time to overseed lawns. Keep the area continually damp until the seed sprouts.
Q. We have several hydrangeas in sunny, dry spots that are healthy and green but never bloom. What should we do?
A. I get more questions about hydrangeas than any other plant. If the flowers were blue when you bought them, and they haven’t bloomed at all in later years, the plants are probably too far north to rebloom. New England winters can be cold enough to kill the flower buds, but not the rest of the plants, so they look perfectly healthy but never flower. This can be a bit of a racket, as plant guarantees usually cover survival but not flowering. Boston is right on the hardiness line, so they bloom in some southern towns but not in western or northern burbs. Some stores ship plants in flower that were grown in the South or greenhouses to all their stores, including northern ones. I bought a pretty $20 pot of blue-flowered hydrangeas at a big-box store this summer for my front steps, and then threw it in the compost pile when it finished blooming, treating it like an annual. If you want something more permanent (and more expensive), buy blue hydrangeas from a local nursery and get a written guarantee if they don’t bloom. Endless Summer is one blue hydrangea that flowers reliably in the North. There is usually no problem with white hydrangeas, which have more winter-hardy flower buds. They are now being bred in shades of pink such as the excellent “Pinky Winky.’’ Unsurprisingly, these are gaining popularity with frustrated hydrangea fans.
Q. I have a beautiful big hydrangea in the front of my house. For years it produced huge blue blossoms. I didn’t cut it back at all. For the past three years, however, I have had only a couple of small blooms. I was told to cut it back. I did, but I’m still getting only a couple of blossoms. What’s my next step?
A. This fall, try cutting back only those stems that have bloomed. These are branched. Don’t touch stems that are straight sticks. These are the new stems that will branch out and bloom next year (with hope).
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