The soil in Montana has high alkalinity, which indicates a pH level higher than 7 on a scale of 1 to 14. A high soil pH level indicates salt in the soil, making it unsuitable for most plants. Some perennial plants can tolerate the alkaline soil and cold winters of Montana, which is primarily in USDA cold hardiness zones 3 and 4. Cut the plants back in the fall and cover with 3 to 4 inches of mulch as winter protection.
The bloom of yarrow is flat and may be white, yellow or red. This drought-tolerant herbaceous plant grows 18 to 36 inches tall and blooms from late spring into fall. Plant in full sun in USDA zones 3 to 9. Space plants 18 to 24 inches apart. Every three years the clump of the yarrow plant can be dug up and divided for additional plants.
The shade-loving astilbe grows 15 to 36 inches tall. Also knows as false spirea, astilbe produces plumes of pink, red or white in late spring. The plumes fade to a rusty-brown as they continue to decorate the landscape. Astilbe self-seeds. Divisions are also used to propagate the plant. Astilbe is cold hardy in USDA zones 4 to 9.
Dianthus plumarius, also known as pinks, is tolerant of high pH levels in soil. The fragrant blooms of this shrubby evergreen perennial may be white, purple or bicolored and display May to July. Plant in full sun to part shade in USDA zones 3 to 8. Dianthus plumarius can reach 12 to 18 inches tall.