When to plant Calendula in Riverside County, CA
Riverside County sits in USDA Zone 10a. Plant Calendula between December 16 (after last frost on February 24) and January 6. A second sowing from August 28 to September 11 extends the harvest into fall.
When to Plant Calendula in Riverside County, CA
What to do in August
Welcome to August in Zone 10a. These are the moves that will have the biggest impact on your growing season.
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Plant your fall garden: calendula
Mid-season soil is hot. Sow a bit deeper than the packet suggests to find cooler, damper ground.
Calendula (Calendula officinalis) is a cheerful, edible-flowered cool-season annual valued by herbalists, chefs, and gardeners alike. Its golden-orange petals are used in salves, teas, and as a saffron substitute. Hardy enough to tolerate light frosts, it blooms prolifically in spring and fall, taking a pause during the hottest weeks of summer.
Riverside County, California is in USDA Zone 10a. The average last spring frost is February 24 and the first fall frost is December 4, giving you a growing season of approximately 283 days.
At an elevation of 1,206 feet, Riverside County receives approximately 15.5 inches of rainfall annually with predominantly loam soil. Summer highs average 102°F, so Calendula may need afternoon shade and extra watering during peak heat. With low rainfall, drip irrigation is essential for growing Calendula successfully. Mulch heavily to conserve soil moisture.
Riverside County Soil Profile
Soil Type
Loam
Soil pH
6.2-7.8
Drainage
Well Drained
Calendula Planting Risk Windows
Percentages indicate frost risk at transplant. The 70% safe window means there is a 30% chance of frost after transplant — suitable for cold-hardy crops or gardeners with frost protection. The 90% safe window is best for tender plants.
Soil Compatibility in Riverside County
How your county's soil matches Calendula's growing requirements.
Soil pH
Your soil pH (6.2–7.8) overlaps with Calendula's range (5.5–7.0), though not a perfect match.
Soil Texture
The loam soil in Riverside County is excellent for Calendula — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.5%). Annual compost additions will help Calendula.
How to Plant Calendula
Fall planting: Sow 14 weeks before your first frost date for a fall harvest.
Succession Planting Calendula
Sow every 5.7 weeks. Last sowing by Sep 25 to harvest before frost.
For a dedicated fall crop, sow by Aug 28.
Calendula Water Budget
Water stress score is 10/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Calendula
Calendula needs approximately 0.5 inches of water per week (2.2" per month). Here's how your county's rainfall compares month by month.
| Month | Calendula Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 3.5" | 0" | ❄️ Dormant |
| Feb | 2.2" | 3.6" | 0" | ✅ Rainfall sufficient |
| Mar | 2.2" | 2.2" | 0" | ✅ Rainfall sufficient |
| Apr | 2.2" | 1.2" | 1" | 💧 Light watering |
| May | 2.2" | 0.4" | 1.8" | 🚿 Regular watering |
| Jun | 2.2" | 0.1" | 2.1" | 🚿 Regular watering |
| Jul | 2.2" | 0" | 2.2" | 🚿 Regular watering |
| Aug | 2.2" | 0" | 2.2" | 🚿 Regular watering |
| Sep | 2.2" | 0.2" | 2" | 🚿 Regular watering |
| Oct | 2.2" | 0.6" | 1.6" | 🚿 Regular watering |
| Nov | 2.2" | 1.5" | 0.7" | 💧 Light watering |
| Dec | 2.2" | 2.4" | 0" | ✅ Rainfall sufficient |
Water needs are for active growing months only (Feb–Dec in Riverside County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Calendula Heat Requirements (GDD)
What are Growing Degree Days (GDD)?
Growing Degree Days measure the total warmth your plants receive during the growing season. Think of it as a "heat bank" — every day above 50°F deposits warmth that helps your plants grow.
Each plant needs a certain amount of accumulated heat to mature. If your county provides more GDD than the plant needs, it's a great fit. If it's close, you may want to choose faster-maturing varieties or start seeds indoors to get a head start.
Calendula Planting Timeline — Riverside County, CA
Calendula Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Transplant Outdoors | January 13 | Jan 13 – Jan 27 |
| Direct Sow | December 16 | Dec 16 – Jan 6 |
| Bloom | February 24 | Feb 24 – Jun 2 |
| Fall Sowing | August 28 | Aug 28 – Sep 11 |
Plant 0.3" deep · 9" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Transplant Outdoors Direct Sow |
| February | Bloom |
| March | Bloom |
| April | Bloom |
| May | Bloom |
| June | Bloom |
| July | — |
| August | Fall Sowing |
| September | Fall Sowing |
| October | — |
| November | — |
| December | Direct Sow |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.5"/week · 1-2 times/week
📅 Days to Maturity
50–70 days
🧪 Soil pH
Needs 5.5–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 10a
📆 Growing Season
283 days in Riverside County
Growing Tips for Calendula in Riverside County
Direct sow Calendula outdoors after February 24 in Riverside County when soil has warmed and frost danger has passed.
With summer highs reaching 102°F in Riverside County, provide afternoon shade for Calendula and water deeply in the morning.
Common pests for Calendula in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
Riverside County receives only 16" of rain annually. Calendula needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Direct-sow in early spring as soon as soil can be worked — seeds germinate in cool soil (50-65°F). In zones 7+, also sow in fall for winter/spring bloom. Deadhead consistently to extend bloom. Plants self-seed readily; save a few spent heads and allow them to drop. Harvest petals when flowers are fully open for best flavor and medicinal value.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Calendula in Other Locations
Frequently Asked Questions
When should I plant Calendula in Riverside County, CA?
Riverside County is in Zone 10a with an average last frost of February 24. Plan your Calendula planting based on this frost date — see the calendar above for exact timing.
What planting zone is Riverside County, CA?
Riverside County, California is in USDA Hardiness Zone 10a. The average last spring frost is February 24 and first fall frost is December 4.
When should I plant Calendula in Riverside County, CA?
In Riverside County, CA, plant Calendula after the last frost (around February 24) and before the first frost (around December 4). Best results when soil holds above 50°F.
What growing zone is Riverside County, CA for Calendula?
Riverside County sits in USDA Zone 10a. Calendula grows reliably in zones 2a through 11b, so it's a good fit here.
Can Calendula grow in Riverside County's climate?
Yes — Calendula grows well in Riverside County's temperate climate. Riverside County averages a 284-day frost-free season, with last frost around February 24 and first frost around December 4.
Your Riverside County Garden Planner — Free
A 22-page printable planner built for Riverside County (Zone 10a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.