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Sunrose – A Great Groundcover That Will Brighten Any Garden
Helianthemum nummularium, aka Sunrose or Rockrose, is a semi-woody perennial sub-shrub or ground cover. Sunroses are originally native to the Mediterranean region, but have been in horticultural production for quite some time, with many cultivars available on the market. They are distantly related to daphnes, hibiscus, hollyhocks and okra, among other plants. As the latin genus name suggests (Helianthemum translates to “sun flower”), these plants grow well in sunny, dry locations, but we’ve also had good results with using them in partial shade.
Luckily for us gardeners here in Colorado, this plant also prefers alkaline soil. This low-growing perennial provides a delightful floral display starting in late May. The profuse blooms hover over a thick mass of low branches that carry small, oval shaped leaves. The flower color is available in shades of red, orange, yellow, pink and white. Perfect for a rock garden, sprawling over the edge of a wall, or in a hot and sunny border area. The silver leaved varieties are semi-evergreen in winter.
PLANT STATS
Scientific Name: Helianthemum nummularium
Plant Type: Perennial Groundcover
Mature Height: 8″-12″
Mature Spread: 18”-24″
Cold Hardiness Zone: USDA zones 5 – 9 (up to 6,000 ft). In colder climates, Sunroses may overwinter more successfully with a mulch covering. Silver leaved varieties overwinter better than green leaved ones.
Water Requirement: Drought tolerant once established. Silver leaved varieties are more drought tolerant and establish sooner than green leaved varieties. Seem to be able to take poor soils very well, and we’ve had good luck is slightly wetter soil as well- very adaptable.
Exposure: Full sun to part shade. We’ve actually had good luck using these plants under trees where there was quite a bit of shade, but full sun will produce the most flowers.
Soil: Sunroses prefer dry, alkaline, rocky or sandy, well-drained loam.
Flower Color & Bloom Time: Various colors are available: white, yellow, orange, red and pink. Blooms May to June.
Winter Interest: Evergreen foliage.
Disadvantages: Roots rot easily in poorly drained soil. Plants don’t do well in prolonged wet soil during winter.
Availability and Sizes: This plant seems to be regularly available at retail nurseries around the front range. It is typically sold in 1 gallon or 4″ pots.
Best Features: The many beautiful flowers that cover this plant when in bloom. The evergreen foliage is also charming when the plant is done blooming.
Maintenance Tip: Prune off old, woody growth in spring. After flowering, the plants may be cut back to encourage new growth. Don’t prune after summer; plants must be allowed time to harden off prior to winter. Plants may be divided in spring (prior to flowering) every 4-5 years.
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Photo of the Day – Silver Cholla in Bloom
This is a photo of Cylinddroppuntia echinocarpa ‘Silver Form’, in bloom in Arvada, Colorado. It’s a beautiful plant that glows with silver spines throughout the year. While no man nor animal would want to brush against it, the bees love frolicking within the sweet nectar-filled blooms.
According to AmericanSouthwest.net, this plant’s native range includes the arid deserts of East California, west Arizona, southeast Utah and south Nevada.
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10 Trees that are Better for Colorado
Attendees in the lobby of the Denver Botanic Gardens where the Tree Diversity Conference was held.
This past Spring, tree enthusiasts from around the region gathered at the Denver Botanic Gardens to listen and learn from various presenters on the theme of Tree Diversity for Colorado. It seems recent crises such as the discovery of Emerald Ash Borer infestation in Boulder has revealed the urgency for members of the Green Industry to seek out more hardy and appropriate tree species for our region. There are other reasons to seek out trees better adapted to our climate. As climate scientists continue to inform us, it is likely that Colorado’s climate will get warmer and drier, providing even more challenging growing conditions for trees. Also, biotic mixing will continue to increase as more people move goods and materials far and wide across the globe. That is the most probable scenario of how EAB was found in Boulder: it was brought there in a wooden crate shipped from Asia. What far-flung exotic pest will next appear in our area?
This year’s conference was the second occurrence of such a gathering in Denver. Several new tree species were presented to the audience, along with some old stand-bys, with a discussion of each tree’s merits.
Although there were several genera that are represented in the group of trees, the two genera with the most candidates are Maples and Oaks. The other genus with multiple species that should get wider consideration for planting in our area is Ulmus (elms). While most elms have been looked over because of Dutch Elm Disease and also the invasive nature of Siberian Elm (Ulmus pulmila), there are a few cultivars that we should consider planting in Denver.
Here are ten trees that were discussed at the conference (out of many others) that you might consider planting in Colorado and the surrounding region:
Acer grandidentatum ‘Manzano’ – Manzano Bigtooth Maple Ht: 20-30’ Wd: 20-30’
Large shrub or small tree with rounded form. The Manzano is a more tree like form of bigtooth maple. Once established, the bigtooth maples are drought tolerant.
Acer miyabei ‘Morton’ – State Street Maple Ht: 50’ Wd: 35’
Rough corky bark and leaf shape are similar to Hedge Maple, but its stronger growth rate and ascending branch habit result in a larger mature size. Excellent drought and cold tolerance. Very adaptable.
Acer saccharum ‘Collins Caddo’ – Collins Caddo Sugar Maple Ht: 45’ Wd: 40’
This maple provides red fall color, but unlike a red maple like Autumn Blaze (Acer x freemanii), the sugar maples are more adapted to the alkaline soils of Colorado’s Front Range urban corridor.
Acer tataricum ‘JFS-KW2’ – Rugged Charm Maple Ht: 28’ Wd: 15’
Compact oval form. More upright than the popular Hot Wings Tatarian maple.
Quercus macrocarpa ’Bullet Proof’ – Bullet Proof Bur Oak Ht: 50-80’ Wd: 50-80’
This large oak sports a massive trunk, deeply furrowed, that supports corky ridged twigs on spreading branches that makes for a broad and rounded canopy. This variety is more resistant to the galls that can affect other Bur Oaks.
Quercus muehlenbergii – Chinkapin Oak Ht: 40’ Wd: 40’
A durable and adaptable oak with narrow lustrous glossy dark green leaves and an open, irregular, rounded habit. Prefers well drained soil.
Quercus robur x alba ‘JFS-KW1QX’ – Streetspire Oak Ht: 45’ Wd: 14’
Dark green leaves of this narrowly columnar tree are mildew resistant. Turning red in autumn, they fall to reveal stiffly upright branches. Similar to Crimson Spire, but does not hold brown foliage through the winter
Ulmus davidiana – David Elm Ht: 40’ Wd: 30’
Medium sized tree, with vase shape. Resistant to Dutch elm disease.
Ulmus propinqua ‘JFS-Bieberich’ – Emerald Sunshine Elm Ht: 35’ Wd: 25’
Grown from seed collected in China, this sturdy, upright-growing elm was selected for superior performance on the hot, arid, windswept plains of western Oklahoma. Handsome, deeply corrugated leaves emerge coppery-bronze and mature to glossy green.
Ulmus japonica x wilsoniana ‘Morton’ – Accolade Elm Ht: 70’ Wd: 60’
Arching limbs and a graceful vase shape (similar to the American elm) characterize this hybrid elm selected and tested at Morton Arboretum. Glossy, dark green foliage changes to yellow in the fall and is resistant to elm leaf beetle feeding.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.