Silphiums: Strange and wonderful

By Larry Cornelis – President, Sydenham Field Naturalists

I like tall flowering plants in my garden.

I’ve found most gardeners don’t like tall plants, always relegating them to the back of gardens.

I think to genuinely appreciate them, you need to get up close and personal so I plant them upfront.

My favourite tall native wildflowers are in the genus Silphium, and we have three species of them locally.

They are in the Asteraceae family.

Of the three species one is adventive, introduced probably by trains from the US Midwest (found growing along railways locally), and the other two are very rare in Southwest Ontario.

Silphium terebinthinaceum, Prairie Dock

Submitted photo

This is my favourite wildflower in my garden. Prairie Dock have huge, hairy, sandpaper-like basal leaves that can be up to 15” x 20” in size.

The hairiness helps them dissipate heat from the sun.

If you press a leaf between your hands, it will feel cool, even in the direct sunlight.

From ground level, the smooth flower stalks rise above the large basal leaves to an amazing 8 to 10’ high.

The stalks branch out near the top and support numerous 3” yellow sunflower like blooms.

Pollinators, especially bees and butterflies are attracted to the flowers for both the nectar and pollen.

When the seeds began to develop, songbirds gorge themselves on them.

From the first blooms opening, there is always activity around my Prairie Dock.

Prairie Dock is native to Southwest Ontario.

Silphium perfoliatum, Cup Plant

Submitted photo

Cup Plant is another large robust plant with unique features.

The large square stalks appear to pierce through the large pairs of leaves.

This forms a cup (hence the common name) that can hold water.

Insects and birds can make use of this water source.

Cup Plant is also very tall growing to 6 to 8’ high.

It is very leafy with pairs of leaves up the stalks although diminishing in size towards the top. The numerous flowers are also approximately 3” in diameter and like Prairie Dock attract bees, butterflies and birds.

Cup Plant is a native species.

Silphium laciniatum, Compass Plant

Submitted photo

Compass Plant may have the most unique leaves of the three species.

They are very large deeply lobed leaves that are also very rough to the touch.

Being deeply lobed into a series of narrow segments and to receive maximum sunlight the leaves are oriented facing north and south.

Hence the name ‘Compass Plant’ by indicating the north south axis.

There are large basal leaves and there are smaller leaves arranged alternately up a very hairy stalk which can also be 8’ tall.

The snow-white long hairs set this Silphium apart from the other two.

Compass Plant is the first of the three to bloom, usually in late June or early July.

Compass plant also attracts and supports many pollinators and songbirds.

This is the adventive species found growing along railways.

These Silphiums are standouts in the garden eliciting attention from everyone who sees them.

Their ecological values are incredible making them a must have in the native plant garden or any garden for that matter.

The Sydenham Field Naturalists offer these species at their native plant sale in May.

Check out the website,, for details.

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