When to plant Sweet Alyssum in Contra Costa County County,
Plant Sweet Alyssum in Contra Costa County County, when soil hits 50°F — usually December 25. Continue planting through January 15 for the spring crop. A second sowing from September 20 to October 4 extends the harvest into fall.
When to Plant Sweet Alyssum in Contra Costa County, CA
June in Contra Costa County, California — your action list
If you only do a handful of things in the garden this June, make it these. They're sequenced around your zone's frost timing.
Sweet Alyssum (Lobularia maritima) is a low-growing cool-season annual prized for its honey-scented clusters of tiny white, pink, or purple flowers. A workhorse border plant, it tolerates light frost, self-seeds readily, and attracts beneficial insects throughout its bloom season. In warm climates it often re-blooms in fall after summer heat fades.
Contra Costa County, California is in USDA Zone 9b. The average last spring frost is February 26 and the first fall frost is November 29, giving you a growing season of approximately 276 days.
At an elevation of 88 feet, Contra Costa County receives approximately 19 inches of rainfall annually with predominantly loam soil. Summer highs average 93°F, providing good warmth for Sweet Alyssum during the growing season. With low rainfall, drip irrigation is essential for growing Sweet Alyssum successfully. Mulch heavily to conserve soil moisture.
Contra Costa County Soil Profile
Soil Type
Loam
Soil pH
6.7-7.8
Drainage
Well Drained
Sweet Alyssum 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 Contra Costa County
How your county's soil matches Sweet Alyssum's growing requirements.
Soil pH
Your soil pH (6.7–7.8) overlaps with Sweet Alyssum's range (6.0–7.5), though not a perfect match.
Soil Texture
The loam soil in Contra Costa County is excellent for Sweet Alyssum — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (3.0%). Annual compost additions will help Sweet Alyssum.
How to Plant Sweet Alyssum
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Succession Planting Sweet Alyssum
Sow every 5.1 weeks. Last sowing by Sep 30 to harvest before frost.
For a dedicated fall crop, sow by Sep 20.
Sweet Alyssum Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Sweet Alyssum
Sweet Alyssum 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 | Sweet Alyssum Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 4.1" | 0" | ❄️ Dormant |
| Feb | 2.2" | 4.5" | 0" | ✅ Rainfall sufficient |
| Mar | 2.2" | 3" | 0" | ✅ Rainfall sufficient |
| Apr | 2.2" | 1.5" | 0.7" | 💧 Light watering |
| May | 2.2" | 0.6" | 1.6" | 🚿 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" | 0.7" | 1.5" | 🚿 Regular watering |
| Nov | 2.2" | 1.6" | 0.6" | 💧 Light watering |
| Dec | — | 2.7" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Feb–Nov in Contra Costa County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Sweet Alyssum 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.
Sweet Alyssum Planting Timeline — Contra Costa County, CA
Sweet Alyssum Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Transplant Outdoors | January 22 | Jan 22 – Feb 5 |
| Direct Sow | December 25 | Dec 25 – Jan 15 |
| Bloom | February 26 | Feb 26 – May 28 |
| Fall Sowing | September 20 | Sep 20 – Oct 4 |
· 6" apart · Rows 8" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Transplant Outdoors Direct Sow |
| February | Transplant Outdoors Bloom |
| March | Bloom |
| April | Bloom |
| May | Bloom |
| June | — |
| July | — |
| August | — |
| September | Fall Sowing |
| October | Fall Sowing |
| November | — |
| December | Direct Sow |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.5"/week · Only during dry spells
📅 Days to Maturity
45–60 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 9b
📆 Growing Season
276 days in Contra Costa County
Growing Tips for Sweet Alyssum in Contra Costa County
Direct sow Sweet Alyssum outdoors after February 26 in Contra Costa County when soil has warmed and frost danger has passed.
Your generous 277.0-day season in Contra Costa County allows multiple plantings of Sweet Alyssum. Sow every 22.0 days for continuous harvest.
Common pests for Sweet Alyssum in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
Contra Costa County receives only 19" of rain annually. Sweet Alyssum needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Surface-sow seeds — they need light to germinate. Direct-sow as soon as soil can be worked in spring; in zones 7+ also sow in fall. Thin to 6 inches apart. Shear back hard in midsummer when heat causes dormancy — plants recover and re-bloom when cool weather returns. Self-seeds prolifically; allow a few plants to set seed for a perpetual colony.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Sweet Alyssum in Other Locations
Frequently Asked Questions
When should I plant Sweet Alyssum in Contra Costa County, CA?
Contra Costa County is in Zone 9b with an average last frost of February 26. Plan your Sweet Alyssum planting based on this frost date — see the calendar above for exact timing.
What planting zone is Contra Costa County, CA?
Contra Costa County, California is in USDA Hardiness Zone 9b. The average last spring frost is February 26 and first fall frost is November 29.
When should I plant Sweet Alyssum in Contra Costa County County, ?
In Contra Costa County County, , plant Sweet Alyssum after the last frost (around February 26) and before the first frost (around November 29). Best results when soil holds above 50°F.
What growing zone is Contra Costa County County, for Sweet Alyssum?
Contra Costa County County sits in USDA Zone 9b. Sweet Alyssum grows reliably in zones 3a through 11b, so it's a good fit here.
Can Sweet Alyssum grow in Contra Costa County County's climate?
Yes — Sweet Alyssum grows well in Contra Costa County County's temperate climate. Contra Costa County County averages a 277-day frost-free season, with last frost around February 26 and first frost around November 29.
Your Contra Costa County Garden Planner — Free
A 22-page printable planner built for Contra Costa County (Zone 9b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.