Join us on Wednesday, 5:00pm until dusk, for garden stewardship! Read on for more garden news.
Giving the Grasses a Hand
We have been doing a lot of things in the garden these past weeks: planting raspberries, picking seeds, pruning, and fixing fencing. One of the natural areas ecological tasks has been to prune back, or pull, some of the more aggressive native forbs (non-woody plants). We prefer to let them flower first: they are dazzling in abundant color, nectar for insects and birds. But, when the flowers have finished, seeds form. And for these particular plants, we want to reduce the seed load. So the seed heads are bagged and given away to be sown in other restoration projects. The stems are chopped for compost.
In large restorations, this same method is used to give a competitive advantage to grasses and sedges over forbs, and it is called mowing, done with large tractors over acres sometimes. Grasses grow from a crown of leaves just at ground level. So, when grasses are mowed they simply keep growing. When forbs are mowed, they have to go through a whole hormonal process to create a new growing point on the cut stem. This takes days, maybe even weeks, during which time the grasses gain biomass, strength, and a bigger share of sunlight.
Prairies and savannas are grass dominant. And grasses carry the fires that keep these ecosystems open and diverse. So if we are managing to create and maintain prairies and savannas, we try to give a hand to the grasses. We keep track of species diversity and pay attention to weedy growth, both native and non-native.
Focus on… Jerusalem Artichoke
The curious thing about Jerusalem artichoke (Helianthus tuberosus) is that it’s not an artichoke and it has nothing to do with Jerusalem (other than that the name is a perfect fit). It is actually a sunflower in the genus Helianthus, the same genus as the sawtooth sunflower. A plausible explanation for the strange name is that it is a corruption of the Italian ‘girasole articiocco’ (sunflower artichoke); the edible tuber is supposed to have a taste similar to that of artichoke.
It is another member of the Asteraceae family, so its blooms are composites made up of many tiny disc and ray florets; as with all sunflowers, the ray florets are infertile and only the disc florets produce seeds. In the close-up photo, you can see the some of the ray florets with five tiny petals and the brown anthers forming tubes through which the style grows, pushing out the pollen as it extends (a couple of the florets on the right already have Y-shaped styles protruding). At the back of the bloom, the leafy bract of the involucre is similar to those of sawtooth sunflower, but on Jerusalem artichoke their phyllaries are wider, more triangular, and hairier. The whole plant is hairier, with stiff white hairs that give the stem and underside of the leaves a rough texture. While not really noted in the plant guides that I have read, I find the three main nerves in the leaves very distinctive, helping me pick out this plant from other similar flowers.
Jerusalem artichoke blooms late in the season, making it one of the last flowers we will see in the garden this year. It is a good late season nectar and pollen source for bees, including the common eastern bumble bee (Bombus impatiens) seen in the main photo, and a variety of birds are attracted to feed on the seeds. Have a look for Jerusalem artichoke in the south swale this fall, you can’t miss their 8-foot stems with yellow flowers.
The “Focus On” series is written by Jeremy Atherton, the parent of a Waters 5th grader. He is a research scientist at Northwestern University Medical School. In addition to volunteering at Waters Garden, he is a steward at Riverbank Neighbors and a member of the 47th Ward Green Council.