Goldenrod (Solidago) is beginning to bloom now in meadows, old fields, ditches and roadsides. This 2-6’ tall plant with erect to arching stems is easy to identify with its panicles of tiny yellow flowers. Since it blooms at the same time as the allergy-aggravating ragweed, some people have mistakenly blamed goldenrod for being a cause of hay fever. However, this is an insect-pollinated plant whose pollen is far too heavy and sticky to travel very far in the wind!
There may be over 100 species of goldenrod in North America. Many of these species spread by rhizomes as well as by seeds. Consequently, they can become quite invasive. This is why the goldenrods are thought of as weeds by many home gardeners as well as why they may become problems in nurseries, orchards and Christmas tree plantations.
Goldenrod species are valuable members of native plant communities since they host a huge variety of insect herbivores as well as pollinators such as bees, wasps and butterflies. They are important hosts to beneficial spiders and insect predators such as praying mantids, lacewings, assassin bugs, and ambush bugs. Birds feed on all these insects as well as on the seeds. There is even a fascinating symbiotic association occurring between the goldenrod and a parasitic gall fruit fly. The female of this species lays eggs inside the plant. The larvae eat the inside of stems causing the plant to form a circular gall. As the larva continues to eat plant tissue, it grows large and fat and eventually over-winters inside the gall before it pupates and then emerges the following spring. This gall may be broken open by downy woodpeckers and Carolina chickadees who eat the nutritious larvae during the winter.
There’s an interesting twist to this story! Penn State researchers have discovered that when the male gall flies land on a goldenrod plant and emit their sex attractant, the plants somehow detect this odor and begin to produce chemical defenses that make them less attractive to the female gall flies as well as to other insects that may feed upon them. Insect-damaged plants may also stimulate neighboring plants to produce these defenses. Exactly how the plants do this has yet to be discovered, but it certainly highlights how wonderfully complex plants can be!
Goldenrod is a common plant in the gardens of Europe and England, but hasn’t found as much favor in nurseries or gardens here. It can, however, add color to the late summer perennial border where it provides a nice contrast to asters, bluebeard, and autumn sedum. It also makes an excellent cut flower, and is a great plant for pollinator or butterfly gardens. Cultivars that are shorter and less aggressive than the species have been selected for and include the clump-forming ‘Golden Baby’ (18-24”) and the ground cover ‘Golden Fleece’ (18”). ‘Fireworks’ (3-4’) with its delicate arching stems lined with tiny golden flowers almost looks like a shrub. This cultivar has been described as a slow spreader and supposedly tolerates clay and moister soil so is a good candidate for rain gardens. Goldenrod grows best in full sun to light shade, and isn’t too fussy about soil, although well-drained is generally preferred. Overly fertile soil tends to make them leggy, and taller varieties may need to be staked. Once established, they are fairly drought resistant. Good air circulation around the plants helps prevent powdery mildew, rust and fungal and bacterial leaf spots to which some cultivars are prone. Insect pests can include spider mites and aphids.
No matter whether you are a fan of goldenrod or not, it can’t be denied that this is another one of those plants that can be weedy in some situations but certainly has a vital role to play in nature!