Also known as Rosinweed · 244 saves
Silphium
Silphium, the genus most gardeners know as rosinweed. We track 5 varieties; the ones most used by real gardeners.
The 5 most-saved Silphium varieties
Track your Silphium in Sow
Save the Silphium you grow and get care reminders timed to your zone.
How to grow Silphium
Whats common across all Silphium varieties in our catalog — drawn from the care records of the 5 most-grown of them.
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 244 real gardeners — 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.