When to Plant Lobelia in Denton County, TX
Lobelia (Lobelia erinus) is a cool-season annual prized for the intense cobalt blue that is rare among bedding flowers. It blooms most prolifically in spring and early summer but stalls or dies back during heat peaks above 90°F. In zones 3–7 it delivers a long display; in zones 8–9 it is best treated as a spring annual that fades by midsummer. Trailing types cascade beautifully from containers and window boxes.
Denton County, Texas is in USDA Zone 8b. The average last spring frost is March 10 and the first fall frost is November 20, giving you a growing season of approximately 255 days.
At an elevation of 1,848 feet, Denton County receives approximately 64.5 inches of rainfall annually with predominantly clay soil. Summer highs average 90°F, providing good warmth for Lobelia during the growing season. Clay soil retains moisture well for Lobelia, but amend with compost to improve drainage and prevent root rot. Ample rainfall means less supplemental watering, but ensure good drainage to prevent Lobelia root diseases.
Denton County Soil Profile
Soil Type
Clay
Soil pH
6.7-8.1
Drainage
Well Drained
Monthly Watering Guide for Lobelia
Lobelia needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Lobelia Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.4" | 0" | ❄️ Dormant |
| Feb | — | 2.1" | 0" | ❄️ Dormant |
| Mar | 4.3" | 4.2" | 0.1" | 💧 Light watering |
| Apr | 4.3" | 7.5" | 0" | ✅ Rainfall sufficient |
| May | 4.3" | 9.6" | 0" | ✅ Rainfall sufficient |
| Jun | 4.3" | 10.2" | 0" | ✅ Rainfall sufficient |
| Jul | 4.3" | 7.6" | 0" | ✅ Rainfall sufficient |
| Aug | 4.3" | 8" | 0" | ✅ Rainfall sufficient |
| Sep | 4.3" | 6.4" | 0" | ✅ Rainfall sufficient |
| Oct | 4.3" | 3.5" | 0.8" | 💧 Light watering |
| Nov | 4.3" | 2.4" | 1.9" | 💧 Light watering |
| Dec | — | 1.6" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Mar–Nov in Denton County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Lobelia Planting Timeline — Denton County, TX
Lobelia Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | January 13 | Jan 13 – Jan 27 |
| Transplant Outdoors | January 27 | Jan 27 – Feb 10 |
| Bloom | March 24 | Mar 24 – May 5 |
· 6" apart · Rows 8" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Start Indoors Transplant Outdoors |
| February | Transplant Outdoors |
| March | Bloom |
| April | Bloom |
| May | Bloom |
| June | — |
| July | — |
| August | — |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
Moderate — regular watering
📅 Days to Maturity
70–80 days
🧪 Soil pH
Needs 6–7 · Your soil: N/A
🗺️ USDA Zone
Zone 8b
📆 Growing Season
255 days in Denton County
Growing Tips for Denton County
Start seeds indoors 10–12 weeks before last frost — seed is dust-fine and requires light to germinate; surface-sow and press gently. Keep at 65–70°F. Not reliably direct-sown. Transplant in cool weather, 2–4 weeks before last frost date is acceptable in zones 5+. Shear plants by one-third after the first bloom flush to encourage a second flush in fall. Provide afternoon shade in zones 7+ to extend bloom into summer.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Lobelia in Other Locations
Frequently Asked Questions
When should I plant Lobelia in Denton County, TX?
Denton County is in Zone 8b with an average last frost of March 10. Plan your Lobelia planting based on this frost date — see the calendar above for exact timing.
What planting zone is Denton County, TX?
Denton County, Texas is in USDA Hardiness Zone 8b. The average last spring frost is March 10 and first fall frost is November 20.
Your Denton County Garden Planner — Free
A 22-page printable planner built for Denton County (Zone 8b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.