Thomas Christopher | Be-A-Better-Gardener: Midsummer care for annuals

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My mentor in annual growing and design, Michael Ruggiero, senior curator at the New York Botanical Garden, always said annuals were the plants that most encouraged experimentation. Mike (now retired, but still teaching horticulture) had grown almost everything in his day from orchids to ferns, but he especially liked annuals because of their quick return on the investment of time and effort. Just a couple of months of very part-time work could turn a few packets of seeds into a flourishing garden's-worth of flowers.

That meant, said Mike, you could try out any wild design idea with annuals. Maybe the results would be great — and Mike's annual border at the Botanical Garden campus in The Bronx was the talk of New York's gardeners every summer. And if your idea didn't work, if you didn't like the results? What had you lost? Just step on it, Mike would say, demonstrating with a large, booted foot, and plant some other annuals. Unlike perennial borders, which take a couple of years at least to mature, the new annuals would be in full bloom again by fall.

Annuals do need some special care, though, especially now, at midsummer. Gardeners who were raised on perennials often find annuals challenging, for the two types of flowers demand very different kinds of care. When growing perennials, the goal is thrifty plants, plants that will bloom, but which will reserve enough energy in the roots to over-winter successfully and return from dormancy the following year. Annuals, by contrast are like racehorses: they must go fast for they last but a season. You have to push annuals, giving them abundant resources. Consistent watering is essential, especially in hot, dry midsummer weather, when you must moisten the soil thoroughly, to a depth of at least eight inches, a couple of times a week. You can tell how deeply the soil has been moistened, by the way, by pushing a dowel down into it; the dowel will slip through the moistened soil easily but stop when it encounters the dry soil below.

Fertilization is also important. If you fertilized with an organic, slow-release fertilizer at planting time, that may carry the annuals through the whole season. If, however, you applied a synthetic fertilizer then, chances are that growth will lag by midsummer, requiring a renewed application now. Container plantings, with their restricted root run, have a particular need for fertilization and should be fed with a half-strength dose of some water-soluble fertilizer every couple of weeks.

Deadheading is another chore that is needed to keep annuals blooming. Most annuals will shift gears once they have set seed, and cease producing new blossoms. Accordingly, you should pinch off the fading flowers before they can bear seed to keep the plant in bloom. If you find this chore tiresome, next spring make a point of planting annual cultivars labeled as "self-cleaning," which means that the plants are sterile, incapable of setting seed and so without the need for deadheading.

After putting on an extravagant display in June, spring-planted annuals are likely to be looking ratty by midsummer. This may be a response to heat, which can be fatal to such cool-loving spring annuals as nemophilas (also known as "baby blue eyes") or garden lobelias (Lobelia erinus). In other cases, though, it may simply be a sign that the plants are in need of renewal. Petunias, for example, tend to grow leggy, with flowers borne only at the end of long stems. Cut a fifth of these stems back to leaves close to the main stem, and new shoots will emerge, at which point you can shorten the rest, returning the plants to a compact and floriferous form. Other thread-bare annuals may be cut back by as much as a third with a sharp pair of shears.

No other plants I can think of return so much in flowers for such a small investment of time and resources. A little timely care at midsummer, and you should be enjoying your annuals bloom right through into fall.

Be-a-Better-Gardener is a community service of Berkshire Botanical Garden, located in Stockbridge. Thomas Christopher is the co-author of "Garden Revolution" (Timber press, 2016) and is a volunteer at Berkshire Botanical Garden. berkshirebotanical.org.

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