October 27, 2013

Maine Gardener: Fertilizing is the key to reblooming iris

The plants should be fertilized early in spring to feed the June blooms and again after the the first blooms to feed the later ones.

By Tom Atwell

In late September I received an email from a reader in Nobleboro who has a gorgeous white bearded iris that was just coming into bloom. Her idea when she planted it was to have black and white irises blooming side by side, but she did not see any white blossoms this spring, so I wondered what was wrong.

I knew about reblooming irises, but I didn’t think there were any that bloomed only in the fall – and there shouldn’t be. But sometimes rebloomers don’t do exactly what they are supposed to, especially when they are young or don’t get enough fertilizer.

Her “Immortality” iris is supposed to give a good show of sweetly fragrant blooms in June and then give another good show in September or October, even in areas as cool as Zone 4, as long as you give it a light dose of fertilizer after its first boom and water it when it gets dry. It is considered the best rebloomer, and some of the others might have trouble reblooming in areas colder than Zone 5, which is Maine along the coast.

Reblooming is a trait for which hybridizers yearn. Gardeners love flowers, but most herbaceous perennials and shrubs bloom for a few weeks and are just green for the rest of the season.

Estabrook’s online catalog features several reblooming irises, including the blue “Clarence,” “Victoria Falls” and “Best Bet,” the yellow “Buckwheat” and “Summer Olympics,” the blue and white “Mother Earth,” the pink and white “Rock Star” as well as “Immortality.” O’Donal’s offers “Blue Suede Shoes” and “Orange Harvest.” Other local nurseries and catalogs will have similar selections.

The key to all of these is fertilization. Producing blossoms requires a lot of food, so these plants should be fertilized early in spring to feed the June blooms and again after the the first blooms to feed the later blooms.

The classic reblooming perennial is the yellow “Stella d’Oro” daylily, which was introduced in 1975, the same year we moved into our house. We planted some shortly thereafter, not only because we liked the plant, but in honor of Nancy’s grandmother, whose name was Stella, and that planting still thrives.

In the decades since, hybridizers have introduced hundreds of reblooming daylilies in a rainbow of colors and many different shapes of blossoms.

While some of these will bloom throughout the summer, you will increase the blossoming time if you deadhead the spent blooms, preventing energy from going to the production of seeds. If you skip the deadheading, you get a flush of blossoms in the spring, a period of few blooms, and then another flush in September and October, right up until the first frost.

Deadheading helps other plants with reblooming, as well.

Both gaillardia, or blanket flower, and coreopsis start blooming in mid-summer and will continue blooming into the fall as long as you remove the spent blossoms. Some varieties of salvia, including “May Night,” will rebloom with deadheading.

Geraniums – the perennial with the common name cranesbill, not the annual with the botanical name Pelargonium popular in cemeteries – also bloom throughout much of the summer, with the newer variety “Rozanne” being the best for long-time blooming.

Catmint is another plant that will bloom throughout most of the summer.

It isn’t only herbaceous perennials that rebloom. Several shrubs and small trees will do the same thing.

The most successful is the “Endless Summer” hydrangea series. These shrubs bloom on both this year’s and last year’s growth, so they keep producing flowers from June through the fall freeze, and the blossoms can look good in the garden through the winter, even though no new blossoms are created.

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