Advice by John P. Begeman: Pretty penstemons

Penstemons are native throughout North America. Although the number of species is greatest for temperate climates, there are several excellent species that flourish in dry climates and are, in fact, native to the desert Southwest.

As a group, the desert penstemons have showy flower spikes arising from rosettes of attractive gray-green to blue-green leaves that grow in a mounding fashion 12 to 30 inches tall. Flower spikes shoot up 2 to 3 feet above the leafy base and are lined with showy tubular flowers in bright colors, from red to rose pink to purple, depending on the species. The blossoms attract hummingbirds.

Desert penstemons are hardy and adapted to Arizona's low, middle and high elevations. They're very drought tolerant and do not require fertilization. They grow easily from seed and, once established, reseed readily on their own. The first year's growth is vegetative. Come the following spring, flowering begins. Plants will bloom for several years.

Penstemons require full sun or light-filtered shade. Plants grown in full shade will be thin and sparsely flowered. Although they grow just fine in their native desert soils, penstemons do respond to the incorporation of organic matter into the soil with thicker vegetative growth and more bloom spikes. Water requirements vary somewhat among species, but in general they're quite happy with applications of water twice monthly during hot weather. However, to establish young plants, water twice weekly during the first few weeks after planting to develop a strong root system.

Parry's penstemon (Penstemon parryi) is a favorite because of its numerous bright-pink flowering spikes, a color not often seen among desert bloomers. Flowering begins in early March and continues for several weeks. Leaves are a silvery green and oblong to lance-shaped. Plants vary in overall height from 2 to 4 feet.

Scarlet penstemon (Penstemon barbatus) is a large penstemon growing up to 5 feet tall and 3 feet wide. It has bright red blossoms that appear in late spring in the low desert to early summer at higher elevations.

Firecracker Penstemon (Penstemon eatonii) — as the name implies — has bright, scarlet-red flower spikes rising above attractive green to blue-green foliage. Plants grow to an overall height of 2 to 4 feet. Flowering occurs in late winter and early spring. As with other penstemons, eatonii benefits from organic matter in the form of compost, chipped or ground bark as a mulch placed over the soil to conserve moisture and keep roots cool.

Superb penstemon (Penstemon superbus) blooms from mid-spring to early summer with flowers ranging in color from coral-red to scarlet-red. Leaves are dark green to blue-green in color. Usually 2 to 3 feet high, with extra watering superbus can stretch up to 5 feet, making it ideal for backgrounds to lower-growing desert shrubs. In windy areas, the tall flower spikes of superbus may need staking to hold them upright. 

Finally, penstemons benefit from grooming to remove flower spikes after bloom. However, if you desire plants to re-seed themselves, wait until seed has formed and dropped before pruning off the spent flower spikes. 

"Making New Plants from Cuttings & Layerings" is the topic if this week's garden demonstrations. They will be presented twice on Wednesday, at 9 a.m. at the University of Arizona-Pima County Extension Center, 4210 N. Campbell Ave., and at 1 p.m. at the Wilmot Library, 530 N. Wilmot Road; and at 1 p.m. on Friday at the Oro Valley Library, 1305 W. Naranja Drive.