Even though the Montana State University Cooperative Extension Service doesn't have a specific publication addressing growing hostas, be assured these herbaceous perennials do grow well in the soils and climate of Montana. While gardeners prize the ornate, often heart-shaped leaves of hostas (also called plantain lilies) for use in shady locations, varieties that tolerate the northern summer sun exist. Many hostas produce tall spikes of white or lavender-colored tubular flowers in summer that are sweetly fragrant.
Montana falls into U.S. Department of Agriculture plant hardiness zones 3 and 4, where expected winter minimum temperatures range between -20 to -40 degrees F. Hostas survive the winters of zone 3 quite well; therefore, they can be grown across Montana, as long as other basic growing requirements are met. Since hostas lose their above-ground stems and leaves in winter, they overwinter unscathed in the soil to return the next spring, once temperatures warm.
In general, hostas are "shade lovers." Gardeners use them to provide colorful foliage in clustered masses in woodland gardens or where the shade from a building prevents other popular flowering perennials from growing well. Partial to full shade is a common lighting situation for hostas, but since Montana is far north, the summer sunlight intensity allows many varieties to be grown in sunny beds, too. Ideally, site hostas where they receive direct sun in the morning hours and then shade. Note that varieties that produce leaves with a lot of yellow or white variegation tend to turn brown or "scald" in too much direct sunlight in general.
The Soil is Key
Rainfall across Montana varies considerably thanks to the Rocky Mountains and the rather rainfall-lacking Great Plains. As long as your garden soil is fertile, moist and well draining, the hosta plant will prosper. Near-neutral soil pH is best (5.5 to 8.0), but hostas will grow in soils amended with copious amounts of organic matter, such as compost or well-rotten manure. Avoid planting hostas in areas where the soil remains soggy after rains, as this condition leads to root rot. Do irrigate planting beds to keep the ground moist so hosta leaves do not wilt. Dry soils lead to sickly-looking plants as well as less tolerance to direct sun rays.
If your garden soil is fertile and rich in organic matter, the need for any supplemental fertilization is greatly diminished. Hostas will respond to applications of fertilizer in late spring to midsummer. Use a slow-release, well-balanced (such as 10-10-10) product according to label dosage recommendations. Always replenish organic matter annually, such as allowing leaf litter from trees to mulch the soil or scattering compost or manure across the soil around hostas.
The longer hosta plants grow over the years, the larger the clump becomes (and arguably the more attractive and lush the plants look in the garden). At some point, a gardener may recognize that the clump size is too large or may simply desire more plants. Slicing out one-quarter of a plant (a root ball wedge) and transplanting it either in early spring or late summer after flowering ends is one way to produce more plants and to reduce the size of a large clump.
Since hostas are often grown in cool, shady and moist landscape settings, be on the lookout for damage from hungry snails that eat emerging leaves and stems and can leave large holes in the foliage. You can sprinkle nontoxic iron phosphate pellets on the soil surface, according to the "Sunset Western Garden Book." In fact, hosta varieties with textured or wavy leaves tend to be less attractive to hungry snails.