If you have had the opportunity to see the blue of gentians in bloom, the experience never leaves your memory. Color can range from milky-blue to a rich royal blue. Hues can be as brilliant and clear as an afternoon sky in winter or soft and muted as a foggy summer morning. Blooms may also have stripes and/or spots appearing as overlays inside or out of the trumpet in darker blues and violet-purple. Aging of individual blossoms can, in some species, bring changing shades of blues on individual blooms in a cluster adding to the interest of display.
There is a full range of size and growth habits to fit any garden. Small gardens would be best served using the ground huggers staying close to the ground forming pancakes of bright green. Larger gardens could easily accommodate the upright growers reaching three feet or more in height.
There are a few species of Gentiana that have a reputation of being difficult to grow in the garden. Generally these are the spring blooming Gentiana. Summer and fall bloomers are easily grown. If you have had reasonable success growing other perennials, you will succeed with gentians.
Species Native to the Lower Midwest
There are about six species of gentian native to the the lower Midwest. I have experience with two of these in the garden. G. puberula seed and plants are seen occasionally in catalogs and seed exchange lists. G. decora, G. quinquefolia and G. villosa I have not been able to obtain thus far.
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Easiest to locate on wildflower hikes, garden centers and gardening catalogs is the Closed or Bottle Gentian (G. andrewsii). It was my first gentian and remains in the garden in spite of all the abuse it received from a novice. Placed in the proper place it is easily grown. It does best with moisture and humus rich soil in part shade. Ordinary soil amended liberally with leaf mold or composted manure does well. Less than ideal conditions will usually produce a smaller plant.
G. andrewsii has a central main root that sends stems up from about one foot to over two feet depending upon soil and moisture. Leaves are in pairs and dark green. Flowers are blue, aging to violet, located on the top and upper half of the plant where the leaf joins the stalk. Blooms are from mid-September to October. I have seen the plant in full bloom the middle of November.
The Soapwort Gentian (G. saponaria) is usually found growing in more moist areas of the wild, among thickets and at the woodland edge in acidic soil. When planting in the garden, incorporate a large amount of peat and leaf mold before planting for acidity, then mulch for moisture retention.
Blooms are bottle-shaped, remaining not fully open, in deep blue during October and into November. As the blooms age they take on a purple cast.
Downy Gentian (G. puberula) is usually found in the open among grasses in relatively dry soil. Since it prefers the company of other plants, I would place it with other perennials or ornamental grasses. Similar in size and foliage to the other two described above, the Downy Gentian has hairy leaves. The lovely blue blooms of this species are open and vase shaped. This gentian can be short-lived, but will seed about where happy in the garden.
Non-native Species
The list of non-native gentian is long enough to fill a book. In general, the Asian fall blooming gentians and their hybrids are most easily adapted to Mid-West gardens. My experience remains a bit limited in number of species grown for more than three years. Many more remain on the list to be introduced to my fall garden.To branch out from the natives begin with Everyman's Gentian (G. septemfidia). The common name comes from its tolerance to a wide range of soils and exposure. Truly an easy plant for a novice, or lovely enough for the most accomplished collector. A low grower forming a circle of about 12-18 inches, it has many open stems from a central crown. The blooms are up-turned trumpets of blue, stripped in darker blues. To show this one off at its best plant in threes. Place among large rocks close to a garden path where the intricacy of blooms can be best appreciated.
The Cross-Leaf Gentian (G. cruciata) is the second gentian I would recommend to those new to gentians and seeking guarantees. Tolerant of a wide range of soils and site exposures, it does perform best in decent soil that does not completely dry out. Usually recommended for full sun, mine performs well in high open shade.
Foliage is leather-like and has a gloss over deep rich green color. A basal rosette is formed each year consisting of several stems on mature plants. Stem leaves are lanceolate in shape and arranged in twos with each pair placed cross-wise of the other giving the common name. Individual blooms are somewhat small in terminal clusters. I feel this one is underrated in most gardening literature.
The Willow Gentian (G. asclepiadea) is another easily grown plant producing great reward in flower. The name comes from the shape of the leaves that reach 2-3 inches in length with a tapering tip. Overall height can reach from 1-1/2 to 2 feet, with 3 a possibility in rich moist soil. Soil should be mixed with a large helping of peat or leaf mold. Keep mulched to retain moisture and a cool root zone. Place where it will receive some shade from the hottest part of the day as this species is normally found growing near streams. Flowers are erect along one side of a stem and up to two inches in length, arranged in bunches of up to three. Usually a dark blue spotted inside and marked with pale stripes on the outside. There are white and rose colored forms.
G. dahurica has leaves that are long and narrow, growing from a central rootstock reaching 8 to 10 inches and arranged rather loosely with a casual appearance. Bloom stalks are separate on the crown with many smaller, more narrow, leaves. Bloom clusters are so numerous the deep clear blue flowers end up arranged in a circle around the foliage lying on the mulch. All is rather informal and great for the edge of a woodland garden.