Zone 2

• USDA zone 2 temperatures reach annual average lows of minus 50 degrees Fahrenheit. The sweetfern (Comptonia peregrina) grows from 2 to 4 feet tall and is hardy in zones 2 to 6. This deciduous shrub blooms with small, yellow-green blossoms in spring and has fragrant, fern-like leaves. It prefers sun to partial shade and well-drained, acidic soil. The shrubby potentilla (Potentilla fruticosa) grows from 1 to 3 feet tall and produces yellow flowers from summer through late fall. Hardy in zones 2 to 7, this slow-growing shrub has deciduous blue-green leaves that turn yellow to brown in autumn. It prefers sun to partial shade and moist, well-drained soil.
  
  

Zone 4

• In USDA zone 4, average annual lows reach minus 30 degrees. The southern bush honeysuckle (Diervilla sessilifolia) grows from 3 to 5 feet tall and blooms through summer with yellow blossoms. It is hardy in zones 4 to 8 and prefers sun to partial shade and dry soils. This fast-growing deciduous shrub tolerates drought and has lustrous foliage. The common woadwaxen (Genista tinctoria) grows from 2 to 3 feet tall and produces 3-inch-long racemes of bright yellow flowers from summer through fall. Hardy in zones 4 to 7, this slow-growing, deciduous shrub thrives in full sun and well-drained to dry soils.
  
  

Zone 5

• Shrubs hardy in USDA zone 5 tolerate average annual lows to minus 20 degrees. The shrubby St. John's wort (Hypericum prolificum) grows from 2 to 4 feet tall and is hardy in zones 5 to 8. This deciduous shrub blooms with bright yellow flowers, followed by dry seed capsules. It prefers sun to partial shade and thrives in a range of soils. Shrubby St. John's wort tolerates drought. Michaux's sumac (Rhus michauxii) grows from 2 to 3 feet tall and is hardy in zones 5 to 7. This deciduous shrub blooms in summer with 8-inch-long panicles of yellow-green flowers. Female plants also produce red berries. Michaux's sumac thrives in sun to partial shade and well-drained soil.
  
  

Zone 6

• Low average temperatures in USDA zone 6 reach minus 10. The Arnold Dwarf border forsythia (Forsythia x intermedia "Arnold Dwarf") grows from 3 to 4 feet tall and is hardy in zones 6 to 8. It prefers sun to partial shade and loose soils. This forsythia blooms with pale yellow flowers in early spring and has arching branches. The paleleaf barberry (Berberis candidula) grows between 2 and 4 feet tall and blooms with small, yellow flowers in late spring. This evergreen shrub is hardy in zones 6 to 8 and prefers sun to partial shade and moist, well-drained soil. It has glossy, dark green leaves with spined edges.