Monday, April 24, 2017

Dwarfs for Every Garden

by Tom Waters

The dwarf bearded irises (those classified as miniature dwarf bearded, or MDB) are a charming addition to any garden. With blooms held eight inches (20 cm) or less from the ground, they are the daintiest of all the bearded irises. They are also the earliest to bloom. In my garden, the first ones open a full two months before tall bearded season.

Almost all MDBs grown today fall into one of three categories. All three groups owe their existence to the eastern European species Iris pumila, which came to be used by American hybridizers in the 1940s.

'Liitle Drummer Boy'
The first category is Iris pumila itself. This tiny species is seldom more than 4 or 5 inches (10-12 cm) in height, with just one bloom per stem. (Actually, the stem is often almost nonexistent, most of the height being in the perianth tube formed by the flower parts themselves.) It comes in a range of colors from white and yellow to blue, violet, and purple, usually with a darker colored spot on the falls. There are a number of cultivars produced by hybridizers or selected from wild forms for their garden value. Some of my favorites are 'Little Drummer Boy' (Willott, 1997), 'Hobbit' (Miller, 2004), and 'Royal Wonder' (Coleman, 2013).

'Royal Wonder'
The next two categories came about as a consequence of the creation of the first standard dwarf bearded (SDB) irises in the 1950s. As I discussed in an earlier blog post, the SDBs were the result of crossing Iris pumila with tall bearded irises (TBs). The SDBs averaged about 12 inches (30 cm) in height and would typically have 2 or 3 buds. They are regarded as medians, not as true dwarfs, because of their larger size and occasional branch, something not seen in traditional dwarf irises.

'Alpine Lake'
Shortly after the SDBs appeared, hybridizers crossed them back to Iris pumila to produce irises of truly dwarf stature, but with a little something extra from their TB ancestry: plicata pattern, for example, or wider petals and more flaring form. These were the most common type of MDB in the 1960s, '70s, and '80s. 'Knick-Knack' (Greenlee, 1961), 'Zipper' (Sindt, 1979), and 'Alpine Lake' (Willott, 1981) are good examples of this type.

The third category came about from SDB breeding in an even more direct way. Sometimes crossing two SDBs produces an iris smaller than average. These small ones, if they are 8 inches or less in height, belong in the MDB class, since the definition for that class is based on height, not ancestry. Because so much work has been done to improve the SDB class over many decades, these are often the most "developed" dwarfs in terms of form and variety of color and pattern. Popular examples of this type are 'Dollop of Cream' (Black, 2006), 'Icon' (Keppel, 2008), and 'Beetlejuice' (Black, 2013).
'Dollop of Cream'

Generally speaking, the greater the amount of Iris pumila in a dwarf's makeup, the smaller, earlier, and more adapted to cold winters it will be. Those with less Iris pumila will have larger flowers with greater width and ruffling, a greater range of color patterns, and perform better in warm-winter areas.

There are no official designations for these categories, although hybridizers sometimes identify them by the number of chromosomes: Iris pumila has 32, the SDBs and their small MDB progeny have 40, and the SDB x pumila hybrids have 36.

How can you tell which of these categories and MDB belongs to? Alas, the only way to be sure is to look at the parentage on the Iris Encyclopedia or other resource. In most cases, this will lead you back either to SDBs or to Iris pumila, or else the parentage will be an SDB x pumila cross. If this sort of research interests you, my list of pure Iris pumila cultivars may help make sense of things.

I love dwarfs in all their variety, and happily live in a locale where all kinds grow well. Do you grow dwarfs in your own garden? Which kinds are your favorite?

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