Also known as Rosinweed · 214 gardener saves
Silphium: the varieties gardeners actually grow
Silphium, the genus most gardeners know as rosinweed. We track 5 varieties; these are the ones gardeners actually save and plant, ranked by real saves rather than catalog marketing. Each links to full care, bloom, and live price data.
The 5 most-saved Silphium varieties
Of 5 in the catalog — ordered by how many gardeners actually grow them.
#1 most savedPrairie Dock
Silphium terebinthinaceum
#2 most savedRoughstem Rosinweed
Silphium radula
#3 most savedCup Plant
Silphium perfoliatum
Toothed Rosinweed
Silphium dentatum
Compass Plant
Silphium laciniatum
How to grow Silphium
What the Silphium varieties in our catalog actually agree on — drawn from the care records of the 5 most-grown of them, not from a generic template.
The Silphium year
- Spring CleanupJanuary–March100% of varieties
Cut back old, dead stalks to the ground before new growth emerges
- PlantMarch, April, September and October60% of varieties
Plant bare root or container plants in spring or early fall
- StakeMay and June60% of varieties
Stake tall plants in exposed or windy locations if stems begin to flop
- PropagateSeptember and October40% of varieties
Collect seeds from dried heads in fall for propagation
Do
- Prune back after flowering to maintain shape
- Water regularly during dry spells 🌱
- Deadhead to prolong flowering
- Divide every 3-4 years to maintain health
- Water deeply during prolonged dry spells 🌱
Avoid
- Avoid overwatering in winter ❌
- Avoid overwatering to prevent root rot ❌
- Don’t disturb roots during peak flowering
- Refrain from fertilizing with high nitrogen
What goes wrong with Silphium
| Problem | What you'll see | What to do |
|---|---|---|
| Aphids | Sticky honeydew on leaves | Apply insecticidal soap or neem oil |
| Root rot | Wilting and yellowing leaves | Improve drainage and reduce watering |
| Powdery mildew | White powder on leaves | Improve air circulation and apply fungicide |
| Root rot | Wilting and browning at base | Ensure well-draining soil and avoid overwatering |
| Powdery Mildew | White powder on leaves | Improve air circulation and apply fungicide |
Making more Silphium
Division
- Divide mature clumps in early spring or fall.
- Replant divisions immediately in prepared soil.
Seed
- Tuck seeds into moist soil in early spring.
- Maintain soil moisture for germination over 2-3 weeks.
Silphium questions
How many types of Silphium are there?
The Sow catalog tracks 5 distinct Silphium varieties. The most popular — ranked by 214 real gardener saves — are shown first above.
What zones does Silphium grow in?
Across its varieties, Silphium covers USDA Zones 4–9. Individual varieties differ — each plant page lists its exact range, and Sow filters the catalog to your zone automatically.
When does Silphium bloom?
Most Silphium varieties bloom in mid-summer. Staggering early, mid, and late varieties extends the genus's season in one bed.
Which Silphium should I choose?
Start from the most-saved varieties above — popularity across thousands of gardens is a strong signal of reliability — then filter by your zone and sun. In the Sow app you can preview any of them in a photo of your actual yard before you buy.
Keep exploring
Silphium shows up in
Design with Silphium in your own yard
Snap a photo of your space and see these varieties planted in it — sized correctly, matched to your zone, with care reminders included.
