The Compass Plant (Silphium laciniatum) is a tall, long-lived, low-maintenance perennial member of the sunflower family. It has a rough-haired stem and clusters of eye-catching yellow flowers that grow up at the top of the plant. Known for attracting a variety of pollinators, it's perfect if you want to encourage bees and butterflies to visit your garden.
This meadow flower is traditionally found growing in the American prairies. It's not found as commonly in the wild these days because of the increasing loss of natural prairie habitat. The plant gets its name from the fact that its lobed leaves tend to point in a north-south direction. This would have helped it maximize the sun and water intake it got in the semi-arid, sometimes harsh prairie environment.
Easy to grow and competition resistant, the Compass Plant could be a great addition to your garden, providing you can offer it enough sunlight. Just make sure you position it behind the shorter flowers.
|Botanical Name||Silphium laciniatum|
|Common Name||Prairie Compass Plant, Pilot Weed, Gum Weed, Turpentine Plant|
|Plant Type||Perennial herb|
|Mature Size||Up to 10 foot|
|Sun Exposure||Full Sun|
|Soil Type||A moist, deep, loamy soil|
|Soil pH||Can tolerate a wide range, but ideally 6.5 to 7.5|
|Bloom Time||Late June through August|
|Hardiness Zones||3 to 9|
|Native Area||Prairies of North America|
How to Grow Compass Plants
Compass Plants should be positioned in a sunny spot. They don't like overly-wet conditions, and they need a deep and well-draining soil to accommodate their sprawling root.
Because they can easily grow to be over 10 feet in height, make sure you don't plant them in front of other smaller flowers. They'll end up cutting out their light and block your view of them too.
Flowering from June through August, they make an impressive and natural-looking addition to any garden.
This is a plant that needs sun and plenty of it. Think carefully about where you position it before planting.
Compass plants have a long, tapering central taproot. It's not unusual for them to be measured at well over ten feet in length. For this reason, you'll need to choose a spot where the soil is sufficiently deep enough.
The type you select should also be well-drained, moist to semi-dry, and preferably loamy.
Given that, in the wild, these plants thrive in dry prairie environments, it's no surprise that Compass Plants are fairly drought-tolerant and hardy.
Once established, they won't need much watering unless you're experiencing a particularly dry spell when moist conditions would be helpful.
Temperature and Humidity
These plants do well in a temperate and dry climate. If conditions are too wet and humid, this can result in powdery mildew forming on the leaves of the plant.
Given this is a hardy wildflower, you won't need to worry about providing additional feeding in the form of fertilizer.
Growing From Seeds
Growing from seeds is the most recommended strategy for propagation.
You can either plant them out directly into the ground in the fall, or, after a sixty-day moist stratification period, in the spring. Scarifying the seeds just before planting can also help to encourage good growth.
If you're looking for a plant that will be blooming impressively immediately, the Compass Plant will be disappointing. Although they're incredibly long-lived, often surviving for up to one hundred years, they're slow-growing too. It can take a good couple of years for them to become fully established and to see a full bloom.
This plant can be rather top-heavy as it grows. It isn't suited to windy or sloping positions, and it can be helpful to plant in borders near a wall or fence for additional support.
Because of their long taproot, these plants really do need to be grown directly into the ground. They aren't suited to being grown in containers.
If you want to harvest more seeds directly from existing plants, you can do this in early September. You just need to mill the seeds so you can access the achenes. This is the hard-walled fruit of the sunflower family that needs to be opened to access the individual seed.