What to do this week: It’s time to start supplemental watering, so set up irrigation systems and hoses. Buy an inexpensive rain gauge. If it rains less than an inch each week, water enough to make up the difference, but water flower containers daily in hot weather. Hanging planters sometimes need to be soaked in a tub if the soil mix has dried out so much that it’s impervious to hosing. You can keep planting in containers through the summer and early fall. Grow mint and lemon balm in pots to keep them from spreading. Fertilize annual flowers and roses once a month. Deadhead annuals to keep them producing new flowers, but don’t do it to biennials because they are on a two-year cycle of replacing themselves. Foxglove, sweet William, hollyhock, poppy, columbine, forget-me-not, and feverfew produce seeds that will bloom for you next year. Remove diseased, pest-infested, or yellowing foliage, and stake flopping plants. In the vegetable garden, sow seeds of bean, turnip, lettuce, cabbage, Chinese cabbage, beet, kale, collards, and rutabaga directly into the garden for a fall crop. Cut the top 6 inches of broccoli crops when the buds are about to open, leaving side branches to continue producing for months more.
Q. I have three large rhododendron bushes that seem to flower well some years and not others. This year there were hardly any flowers, and I was envious of other homes’ plentiful bounties. I prune them after they lose their flowers. What am I doing wrong? Should I be feeding them something?
A. You probably accidentally removed the following year’s shoots and flower buds. They form on either side of this year’s spent flower heads. It is tricky, so I don’t deadhead rhododendrons. Don’t prune rhododendrons unless you absolutely have to, anyway, because they hate it. If they have outgrown their space, it is better to dig them up and move them (their roots are shallow) than to try to cut them back.
Q. I would like to buy a book on outdoor plants that grow in the Northeast, one that would tell me a lot about each one, such as what type of fertilizer does it like, whether it needs full sun, etc.?
A. The Taylor’s Gardening Guides published by Houghton Mifflin Harcourt are good. They are about 20 years old now, but there are several of them, each devoted to a relatively narrow subject such as perennials, shrubs, wildflowers, annuals, or vegetables. These books have extensive plant descriptions in alphabetical order with many color photographs. I contributed to Taylor’s “Seaside Gardening’’ volume, but for coastal gardeners, I would recommend a new book by C.L. Fornari, “Sand and Soil: Creating Beautiful Gardens on Cape Cod and the Islands,’’ published by David R. Godine.
This is a good time to divide or plant bearded iris. The Iris Society of Massachusetts (www.massirises.org) will hold its annual sale on July 27, from 11 a.m. to 3 p.m. at Verrill Farm, 22 Wheeler Road in Concord.