Last spring frost: March 4 (50% probability)
First fall frost: November 21 (50% probability)
Frost-free growing season: 262 days
Approximate USDA zone: 9a
The median last spring frost date for San Antonio, TX (ZIP code 78244) is around March 4. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area.
The median first fall frost date for San Antonio, TX is around November 21. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses.
The frost-free growing season in San Antonio is about 262 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side.
Based on frost date patterns, San Antonio falls approximately in 9a. USDA hardiness zones are determined by average annual minimum winter temperatures and guide both plant selection and planting timing for your location.
Start tomato seeds indoors 6–8 weeks before your last frost date (around March 4). That means starting in late June 4 or early July 4 for San Antonio. Transplant outdoors 1–2 weeks after your last frost.