Plant Select is a 25 year old cooperative program combining the efforts of Denver Botanic Garden, Colorado State University and some members of the local green industry. Their intention is to chose, propagate and promote plants that are well-adapted to Colorado conditions, colorful and are either little known or underutilized. The 2011 choices are a particularly excellent group.
Baby Blue Rabbitbrush, Chrysothamnus (Ericameria) nauseosus var. nauseosus is one of the finest native shrubs for the home garden and has tremendous potential in commercial plantings. Claude Barr, author of Jewels of the Plains, calls this species “the gem of the tribe”. It is a native of Colorado from 5000’-9000’ , and sowed itself on our windblown North Boulder property. Unlike the taller, looser, blue and green rabbitbrushes, Dwarf Blue Rabbitbrush grows to a compact mound only 24” high and 30” wide. The fine textured foliage is silvery blue and can grow quite densely. The golden yellow flowers cover the domed form through the fall, making a show that is not only attractive to humans but collects bees, butterflies and beneficial soldier beetles. It is not browsed by deer or rabbits, but the rabbits do like to hide under them.
This tough beauty loves the sun and needs no water once established. In fact, it is better to water it no more than once a week in order to keep the form tight. It does have a tendency for the thin stems to fall open from the weight of flowers and seeds, so it is best to shear off the flowers, cutting 2”-4” after they have finished blooming.
David Salman of High Country Gardens discovered ‘Blonde Ambition’ grass in New Mexico. This larger selection of the native Blue Grama Grass, Bouteloua gracilis, grows to 30”-36”. The seed heads are a chartreuse color that ages to blonde, and they hold up well in the winter garden. Blue Grama has been given the name “Eye-Lash Grass” because of the dainty horizontal flower/seed heads. ‘Blonde Ambition’ is cold hardy to zone 4 and is tolerant of most soils. It is good for xeriscape gardens, requiring little water, and it is low maintenance, needing only to be cut to 2” high each spring. It loves the sun and looks good with other ornamental grasses and taller dryland perennials.
Amsonia jonesii, the Colorado Desert Blue Star, is a western native perennial that has clusters of blue star flowers at the ends of its 10”-14” stems. It blooms from April to June. The color of these ½” tubular flowers must be variable, because descriptions range from sapphire blue, through powder blue to ivory. The autumn color of the foliage is a clear yellow.
The form is upright and mounding to 12”-15” wide. I am glad to learn that although this plant is long-lived, it is slow to develop, and may take 5 years to become glorious. It is reassuring that my bashful 3 year old specimen may need nothing more than time. Desert Blue Star is said to be attractive to bees, but not to rabbits and deer.
Russian Hawthorn, Crataegus ambigua, has been in Colorado for some time, but is not well known and often difficult to obtain. At our nursery, Harlequin’s Gardens, we have a demonstration garden of mostly native shrubs that has not been watered since 2002. The non-native exception in this unwatered garden is Russian Hawthorn which is perfectly adapted to Colorado conditions. It is usually a dense tree, 12’-15’ high and wide with horizontal branching and a rounded form. It’s white flowers smother the branches in April/May and great quantities of round red fruits follow. These make a wonderful show, are usually not messy and are often eaten by the birds. The fall color is a golden yellow.
Like most Hawthorns, Russian Hawthorn does have thorns, but I have not found them difficult to work around. However it is a good idea to thin crowding branches when they are small, because to extract a branch once it is mature is a very difficult job. This is a wonderful small tree for a screen, a specimen, for a wildlife garden or for a very dry and windy site up to 8000’.
One of my favorite native penstemons is Grand Mesa Beardtongue, Penstemon mensarum. The color of the 2’-3’ spikes of flowers is a rich cobalt blue that glows May to June. The evergreen leaves form a loose mat. It has been long-lived and reliable in two locations for us, and in one eastern location, it is only watered once a month. Bob Nold, in his indispensible book, Penstemons, suggests that it not be grown too dry.
Like many penstemons, Grand Mesa Beardtongue has more impact in a group, so plant two or three 12”-15” apart, or crush the dried seed capsules in your gloved hand in late summer and press the seeds into the surrounding ground to encourage a colony. Especially in clay soils, it is best to water no more than once a week and to grow it in full sun. It can be grown up to 9500’.
‘Avalanche’ White Sun Daisy is a South African Osteospermum which I have not yet grown because it is a new introduction. The large daisy flowers are bright white with a yellow and black-dotted eye, that are very long blooming from April to late summer. ‘Avalanche’ grows as an evergreen mat 8”-12” high and 10”-15” wide. In the evening, these blooms fold up, revealing the coppery back of the petals. Two earlier Plant Select Osteospermums have not been long-lived for me, but this one is said to be a superior, longer blooming and longer lived variety. It is reported to grow in dry conditions up to 9000’. It may be better to plant it where it gets winter sun, perhaps with a fine gravel mulch to avoid fungus problems.
A great choice for 2011 Plant Select was Erodium chrysanthum, because it is one tough beauty. It has been in the Harlequin’s Favorites display garden for five years. The silvery green ferny foliage is dense and evergreen, and the five-petalled, geranium-like flowers bloom heavily in spring, then sporadically all summer. The flower color is a sweet pale yellow/cream. Whoever named it “Golden Storksbill” must have been looking at the name “chrysanthum” (meaning “gold”) and not at the flower.
This is a very drought tolerant perennial that is easy to grow and holds up for a long time. It looks delicate and petite, but has a big taproot and can grow from 10” to 24” in diameter and only 6”-8” in height. Erodium chrysanthum excels as a specimen, as a ground cover, in a group, or along a path. She will make your thumb look green.
‘Avalanche’ White Sun Daisy will have to prove itself to me, but all the others in this year’s Plant Select pick live up to their promotion as being Durable Plants for the Garden.