Roughstem Rosinweed (Silphium radula)

Also known as: Starry Rosinweed

The plant you're referring to is the Roughstem Rosinweed (Silphium radula), a perennial from the aster or sunflower family. It stands upright with yellowish-green flowers and is often used in borders. This plant thrives in dry, poor soil and can fall over in rich or wet conditions.

In This Article

Care Tips Water Sunlight Temperature Soil Fertilize Prune Propagation Repotting

Attributes of Roughstem Rosinweed

Lifespan

Perennial

Plant Type

Herb

Plant Height

91 cm to 1.8 m

Spread

60 cm to 90 cm

Leaf Color

Green

Flower Size

2.5 cm to 8 cm

Flower Color

Brown

Images of Roughstem Rosinweed

Quickly Identify Roughstem Rosinweed

Identified by its large, rough, and toothed leaves as well as its tall flowering stalks reaching up to 7 feet. The yellow flowers are arranged in a daisy-like pattern and its leaves often orient North-South, giving it the name Compass Plant.

Scientific Classification of Roughstem Rosinweed

Phylum

Vascular plants

Class

Dicotyledons

Order

Asterales

Family

Daisy

Genus

Rosinweeds

Species

Roughstem Rosinweed

Planting and Growing of Roughstem Rosinweed

Care Difficulty

Easy

Watering Schedule

Every 2 days

Sunlight Requirements

Full sun

Sunshine Duration

6-10 hours

Ideal Temperature

65-75℉

Soil Type

Potting Mix, Peat Mix

Soil pH

6.5-7.5

Fertilizer Type

Balanced

Pruning Season

Spring, Summer

Pruning Area

Branches, Leaves

Pruning Frequency

2 times a year

Repotting Season

Spring

Pot Type

Plastic, Ceramic

How to Water Roughstem Rosinweed?

When watering Silphium radula, aim for about 150 milliliters until the top inch of soil feels moist but not waterlogged. It's crucial to ensure proper drainage to prevent root rot.

What are the symptoms of an underwatered Roughstem Rosinweed? ›

What should I do if my Roughstem Rosinweed is not getting enough water? ›

What are the symptoms of an overwatered Roughstem Rosinweed? ›

How to save an overwatered Roughstem Rosinweed? ›

What Are the Sunlight Requirements for Roughstem Rosinweed?

Sunlight Requirements: Full sun

Duration of light: 6-8 hours daily

Silphium radula benefits from full sun; providing at least 6-8 hours of sunlight promotes vigorous growth and helps in maintaining vibrant foliage and abundant flowering.

How much sunlight does Silphium radula need? ›

What are the solutions for inadequate sunlight? ›

How does Silphium radula benefit from ideal sunlight? ›

More About Sunlight Requirements Techniques→

What Is the Ideal Temperature Range for Roughstem Rosinweed?

Ideal Temperature: 65 ~ 75℉

The optimal temperature range for growing Silphium radula is between 65°F and 75°F. This range allows the plant to perform photosynthesis efficiently while minimizing stress factors related to temperature fluctuations.

What Soil is Best for Roughstem Rosinweed?

Soil type: Sandy soil, Sandy loam

Soil PH: 6.5 ~ 7.5

Silphium radula thrives in well-draining soil, as it helps to prevent root rot. This type of soil ensures that excess water is quickly dispelled, allowing roots to breathe and access vital oxygen, which is crucial for the overall health and growth of the plant. The plant benefits from nutrient-rich soil, which supports its robust growth and vibrant foliage. A well-balanced presence of essential nutrients helps Silphium radula to develop strong stems and promotes frequent blooming. While Silphium radula prefers sandy loam, it can also benefit from soil that retains moderate moisture. This helps the plant during dry spells, providing a sustained supply of water without the consequence of waterlogging.

How to Fertilize Roughstem Rosinweed?

Fertilizer type: Balanced

For Silphium radula, it is crucial to maintain a balance in its nutrient supply. Typically, use a balanced liquid fertilizer diluted to about 1/4 strength, applying about 1 liter per square meter for liquid fertilizers and around 30 grams per square meter for slow-release forms.

How to Prune Roughstem Rosinweed?

Pruning Time: Spring, Summer

Prune Silphium radula when it is in its active growth period, usually during spring and summer. This ensures the plant has the energy to heal and grow back vigorously after pruning. Begin by removing old, woody, or dead stems. This encourages new growth and enhances the overall vitality of the plant. Always make your cuts at a 45-degree angle, away from the bud. This angle allows water to run off easily and prevents rot at the cut site. Avoid heavy pruning late in the season to prevent stimulating new growth that could be damaged by frost. Leaving some foliage can also help insulate the plant during colder months. More About Pruning Techniques→

How to Propagate Roughstem Rosinweed plant?

Propagate Time: Spring, Late Spring, Early Summer

Begin by filling seed trays with a good quality seed-starting mix. Sow the seeds on the surface and cover with a thin layer of soil. Keep the soil consistently moist and place trays in a warm location with bright, indirect light.

Select healthy, non-flowering shoots from the parent plant. Use sharp pruners to cut below a leaf node. Remove lower leaves and dip the cutting in rooting hormone to encourage root development. Place in a container with damp potting mix.

Once seedlings have developed a few sets of true leaves, they can be transplanted to individual pots. Handle seedlings carefully to avoid damaging their tender roots. Provide adequate light and gradually acclimate them to outdoor conditions.

More About Propagating Techniques→

How to Repot Roughstem Rosinweed plant?

Repotting frequency: Every 2-3 years

Silphium radula generally signals its need for repotting when its roots can be seen growing out of the drainage holes or when the plant growth becomes noticeably stunted. Typically, the best time to repot is at the beginning of growing seasons like spring or autumn when the plant is actively growing and can adjust more smoothly to a new pot and soil environment.

Selecting the proper pot is crucial to the plant's health. Choose a pot that is slightly larger than the current one to allow root expansion, with adequate drainage holes to prevent waterlogging. This prevents root rot, which ensures longevity and vibrant growth for your Silphium radula.

Opt for well-draining, sandy loam soil to promote healthy root development. This type of soil composition prevents water retention that can lead to root diseases and allows for ample aeration, ultimately facilitating robust growth and blooming of Silphium radula.