Monthly Archives: September 2015


What’s Blooming 9/21/2015


For many, the beginning of fall is signaled by the appearance of pumpkin spice lattes. But gardeners might take more notice of the rows of mums appearing outside every box store in the valley. If you like mums, but are tired of purchasing them year after year, consider the Aster. As one IBG gardener likes to call them, “the harbingers of autumn,” are just now coming into bloom. Reliable, hardy perennials, Asters provide a burst of late fall color as well as a last stop for pollinators before winter. Asters come in a variety of colors and sizes, and require very little upkeep. The only challenges with Asters are that many are susceptible to powdery mildew and taller varieties can become unwieldy; however, both of these problems are overcome by selecting the right variety.

AsterA favorite variety of Aster here at the garden is ‘Purple Dome’. Aster novae-angliae ‘Purple Dome’ is an all-purpose Aster whose scientific name means “of New England”. Unlike New York Asters (Aster novae-belgii) New England Asters have thick stems and hairy leaves, and are generally taller. ‘Purple Dome’, however, has been cultivated to maintain a low, bushy habit, making it easier to care for than taller asters that might require staking. Covered in deep lavender flowers, this cultivar generally blooms from late August until frost. As an added, bonus, ‘Purple Dome’ is mildew resistant.

Another low grower is Aster x frikartii ‘Monch’. Compact, but resplendent with light lavender blooms all fall, ‘Monch’ typically grows to only two feet tall, making it a perfect plant for a perennial border, and is also resistant to powdery mildew.

Possibly the best thing about Asters is that, to keep them looking their best, they need to be divided every two to three years; this means, of course, free plants! After your initial purchase, you will have access to a continual supply of these hardy perennials forever!

If you want to learn more about dividing plants, come to our education class, “Divide and Conquer” at IBG on September 29th.

If you’re in search of an Intermountain native option in the world of Aster, Machaeranthera canescens, commonly known as hoary tansyaster or hoary aster might be just what you’re looking for. It is a highly variable species that occurs throughout the western portion of North America as well as in some north central states. It can be found in a wide variety of habitats, and is particularly common in dry and/or disturbed sites, shrub steppes, and meadows. It is native to the Boise Foothills and is one of the few late summer flowering plants in this region. It is considered a short-lived perennial, but it often acts as an annual or biennial. Its latin name “canescens” refers to the small, gray hairs that cover its stems. Its leaves are long and narrow and often have sharply toothed margins. Flower heads appear singularly or in multiples at the ends of branches. A series of small, light green bracts form a cup below each flower head. The flower heads consist of disc florets that are a striking yellow color and ray florets that are pale to dark purple.

Aster2Hoary tansyaster can be found throughout the Lewis and Clark Native Plant Garden, as well as in the Foothills Native Plant Garden, along the Wilderness Trail, and in our restoration areas.

So, if you’re looking to get more bang for your buck year after year, and desire a more naturalistic option than mums, consider choosing an Aster. You’ll love the color it adds to your fall garden, and the pollinators will thank you, too!


What’s Blooming 9/14/2015


Summers in the Treasure Valley are bookended by the yellow flowers of two of our most abundant native shrubs. In late spring, bitterbrush bursts into bloom and gives the foothills a creamy yellow hue. As summer comes to a close, the foothills turn yellow-gold with the flowers of rabbitbrush. With the rabbitbrush now beginning to bloom, it is clear that fall is imminent.

rabbitbrush1The two most common species of rabbitbrush in our region are gray rabbitbrush and green rabbitbrush. Both are in the sunflower family (Asteraceae) and are related to a couple of other well-known late summer/fall flowering genera, Aster and Chrysanthemum. Gray rabbitbrush (Ericameria nauseosa), also known as rubber rabbitbrush, is a densely branched shrub that reaches an average height of 3 feet. Leaves are narrow and numerous, and stems and leaves are covered in short, white, felt-like hairs giving the plant a gray appearance.

Many plants in the sunflower family have inflorescences that are a combination of ray and disk flowers clustered tightly together and arranged in such a way that the inflorescence appears as a single flower. Consider sunflowers, for example. What appear as petals around the outside of a sunflower are actually a series of individual flowers called ray flowers. In the center of a sunflower are dozens of disk flowers. The flowers of gray rabbitbrush lack ray flowers, and instead are clusters of 5 or so disc flowers. The flower clusters form at the tips of each branch. When the plant is in full bloom, the flowers create a sheet of yellow-gold atop white-gray foliage – a sight to behold.

Native Americans used the flexible branches of gray rabbitbrush to weave baskets and the flowers to make dyes. The stems contain a latex sap (which explains the common name, rubber rabbitbrush). Native Americans would occasionally chew the stems to help relieve hunger and thirst. A tea was made from the stems to treat coughs, colds, chest pains, and toothaches, and bundles of branches were burned to smoke animal hides.

rabbitbrush2Green rabbitbrush (Chrysothamnus viscidiflorus) is typically smaller than gray rabbitbrush, reaching a maximum height of about 3 feet. Its stems and leaves appear similar to gray rabbitbrush except they lack the dense, white hairs. The stems and leaves also have a stickiness to them, and the leaves are often twisted or curled. The flowers are clusters of 5 or so disc flowers (again, no ray flowers) that form at the tips of the branches. Both species of rabbitbrush are commonly found together in nature, and so growing together in a garden setting they look right at home.

All of our native shrubs have ornamental potential, but rabbitbrush is particularly high on that list. It provides year-round interest and can be easily maintained in an attractive form simply by cutting it back by a third or more each spring. If it becomes too large and gangly, it can be cut back nearly to the ground and will regenerate, quickly returning to a more manageable form. Its vibrant, yellow, late summer flowers complement those of goldenrod and help ring in the harvest season.

You can witness both species of rabbitbrush in full bloom this fall by visiting Idaho Botanical Garden and strolling through both the Idaho Native Plant Garden and the Lewis and Clark Native Plant Garden.


What’s Blooming 9/7/2015

Maximilian Sunflower

Helianthus maximiliani

 IMG_4158 Maximilian Sunflower is an herbaceous perennial native to the Great Plains regions of central North America. It is usually found in dry open areas such as prairies and bluffs. Helianthus maximiliani is hardy in zones 4-9 and grows 3-10 feet tall and 2-4 feet wide. Maximillian Sunflower is in the Asteraceae family and has a yellow composite flower which consists of disk and ray florets. It flowers August through September and reseeds freely. Cut it back after it flowers in the fall if you want to minimize reseeding. Maximillian Sunflower has long narrow leaves which are alternate, coarse, and covered with fine white hairs. This plant prefers full sun and can handle dry to medium water conditions. If overwatered it has the tendency to flop. To prevent flopping cut the plant down to two or three feet in June. It will grow in most soil types but prefers well drained soil conditions.

Maximilian Sunflower grows from a rhizome. The rhizome is edible and it provided food similar to Jerusalem artichokes for the Native Americans. Maximilian Sunflower also attracts beneficial insects and birds. Maximilian Sunflower is used as an ingredient in range seeding mixtures to provide high quality forage for livestock.   It also provides food and cover for wildlife. This sunflower is difficult for squirrels to climb so often birds get the seeds.

Helianthus maximiliani is a good perennial for the back of a border. It is a great addition to a garden because it is showy in the fall when most perennials are done flowering. Maximilian Sunflower is also great as a cut flower. You can find it at the IMG_4154Idaho Botanical Garden in the Herb Garden or near the Children’s Garden.