San Antonio Frost Dates: When to Plant & Protect Your Garden

San Antonio’s Last Spring Frost Date: February 28

San Antonio’s median last spring frost occurs on February 28, based on NOAA’s 1991-2020 climate data from weather station USW00012921. Your 90% safe date — when frost risk drops to just 10% — falls on March 22, creating a 22-day gap that experienced gardeners navigate carefully.

Your first fall frost typically arrives November 30, giving you 275 frost-free growing days annually. This puts San Antonio squarely in USDA Zone 9a, where winter lows reach 20-25°F. The area gained this warmer classification in the 2023 USDA Plant Hardiness Zone Map update, reflecting documented warming trends in the region.

These dates represent 50th percentile probabilities — half of all years see frost earlier, half later. The February 28 median means you have a 50% chance of frost after this date. Smart gardeners use the March 22 date (90% probability) for frost-sensitive crops like tomatoes and peppers, while cold-hardy vegetables like broccoli and kale can go in the ground weeks earlier.

Should You Cover Your Plants Tonight?

Protect tomatoes, peppers, and eggplant when temperatures drop to 32°F or below — these crops suffer cell damage at the freezing point. Citrus trees need protection at 28°F, while established fig trees can handle brief dips to 20°F without cover.

Radiative frost forms on clear, calm nights when heat radiates away from plant surfaces. Row covers, old sheets, or even cardboard boxes trap this radiant heat effectively. Advective freezes — driven by cold wind masses — require different tactics. String Christmas lights through citrus canopies or wrap trunks with tree wrap for these harder freezes.

Check your frost percentile data before deciding. A 10% frost risk (March 22 date) might warrant protection for valuable plants, while a 50% risk (February 28 date) demands covering anything frost-sensitive. Water plants thoroughly before expected frost — moist soil holds more heat than dry ground. Remove covers once temperatures rise above freezing to prevent overheating. Plastic directly touching plant tissue causes more damage than no protection at all.

What Can You Plant After the Last Frost?

Plant tomatoes, peppers, and eggplant 2-4 weeks after your March 22 safe date — typically mid-April for San Antonio. These warm-season crops need soil temperatures above 60°F to establish properly. Okra, sweet potatoes, and melons require even warmer conditions; wait until early May when soil hits 65°F consistently.

Beans and squash can go in 1-2 weeks after the safe date, around early April. These crops tolerate light frost better than tomatoes but still prefer warm soil. Corn plants well from mid-March through April, with successive plantings every two weeks for continuous harvest.

Herbs like basil, oregano, and rosemary transplant safely after the last frost date. Basil is particularly frost-sensitive — one cold night ruins an entire planting. Start these herbs indoors 6-8 weeks before your safe date for transplanting in mid to late March. [INTERNAL_LINK: when-to-plant-tomatoes-san-antonio-tx]

By mid-April, San Antonio accumulates approximately 1309 Growing Degree Days (base 50°F) — 18% of your annual total of 7349 GDD. This rapid heat accumulation explains why warm-season crops establish quickly once planted at proper timing.

Your Fall Planting Window

Work backward from your November 30 first frost date to determine fall planting schedules. Frost-tolerant crops like broccoli, kale, and carrots need 10-14 weeks to mature, placing their planting window in early to mid-August. These vegetables actually improve in flavor after light frost exposure.

Frost-susceptible crops like tomatoes, peppers, and eggplant require 12-16 weeks before first frost to produce meaningful harvests. Plant these by early August for fall production, though summer heat stress makes spring plantings more reliable in San Antonio’s climate.

Heat-loving crops like okra need different calculations entirely. Okra continues producing until hard freeze (28°F or below), often extending harvest into December. Plant okra by late July for fall production, giving it 16+ weeks of growing time. This timing captures the September-October sweet spot when temperatures moderate but frost hasn’t arrived.

Spinach, lettuce, and other leafy greens tolerate light frost well. Plant these 8-10 weeks before first frost — typically early September. San Antonio’s mild winters often allow continuous harvest of cold-hardy greens through February, bridging the gap to spring plantings.

Your Frost Date Comparison Table

The 90% spring date (February 3) represents extreme early frost — only one year in ten sees frost this late. Use this date for cold-hardy vegetables like cabbage and peas that tolerate frost well. The median dates (February 28 spring, November 30 fall) represent typical years where half experience frost earlier and half later.

Your 90% safe spring date (March 22) provides crucial guidance for frost-sensitive plantings. Only one year in ten experiences frost after this date, making it the standard recommendation for tomatoes, peppers, and other tender crops. The corresponding fall safe date (November 3) shows when frost becomes highly likely — 90% of years see frost by this date.

This data comes from weather station USW00012921, representing San Antonio’s specific microclimate conditions. Suburban heat islands may extend your frost-free period by several days, while rural areas or low-lying spots may experience frost earlier than these station-based dates indicate.

Your Monthly Growing Degree Days

Growing Degree Days (GDD) measure heat accumulation above 50°F — the base temperature for most vegetable growth. San Antonio accumulates 7349 GDD annually, supporting both cool-season and warm-season crop production. January’s 142 GDD allows slow growth of cold-hardy vegetables like kale and spinach planted the previous fall.

March’s 388 GDD creates ideal conditions for cool-season crops like broccoli, lettuce, and peas. These vegetables prefer moderate heat accumulation without summer’s intensity. June’s 973 GDD represents peak growing conditions for warm-season crops, though some vegetables begin showing heat stress as temperatures climb.

August’s 1096 GDD — the year’s highest monthly accumulation — pushes heat-sensitive crops to their limits. Cool-season fall plantings struggle during this period, requiring shade protection or delayed planting until September. December’s 166 GDD maintains slow growth of cold-hardy vegetables through winter months, allowing continuous harvest in many years.

Your Fruit Tree Compatibility Guide

San Antonio accumulates 350 chill hours in a typical year (range: 200-450), satisfying requirements for 8 of 8 listed fruit species. Chill hours measure time below 45°F needed for proper fruit development. This moderate accumulation eliminates high-chill fruits like standard apples and cherries while supporting excellent low-chill and no-chill alternatives.

Apple varieties like Anna, Dorsett Golden, and Ein Shemer thrive with San Antonio’s chill hour pattern. Standard Northern apples requiring 800+ chill hours fail to fruit reliably here. Southern highbush blueberries like Misty, O’Neal, and Star perform far better than Northern varieties needing 1000+ chill hours.

Avocados and bananas represent no-chill options that leverage Zone 9a’s warm winters while requiring protection during occasional hard freezes. Dragon fruit and figs combine heat tolerance with minimal chill requirements, making them ideal permanent landscape additions. [INTERNAL_LINK: san-antonio-tx-hardiness-zone]

Your Zone 9a Growing Advantages

Zone 9a designation means your minimum winter temperatures stay between 20-25°F, eliminating many cold-damage risks that plague northern gardeners. This classification opened up in the 2023 USDA Plant Hardiness Zone Map update, reflecting documented warming trends across the region. Most perennial herbs, fruit trees, and ornamental plants rated for Zone 9 survive your winters without protection.

The real challenge isn’t winter cold but summer heat. Zone 9a tells you what survives winter minimum temperatures, but July and August highs above 95°F stress cool-season crops and some warm-season varieties. This two-axis climate reality — mild winters, intense summers — shapes your entire growing strategy.

Your 275-day frost-free growing season ranks among the longest in the continental United States. This extended season allows two complete crop cycles for fast-maturing vegetables like lettuce, radishes, and beans. Many gardeners run continuous succession plantings from March through October, maximizing production from available space.

Bexar County’s 2.0 million population includes 428,306 owner-occupied households, representing substantial potential garden space across suburban and rural areas. This large gardening community supports extensive local nursery infrastructure and active extension service programming tailored to Zone 9a conditions.

Your Seasonal Planting Calendar

January through February focuses on cool-season crop establishment. Plant onions, garlic, and shallots by mid-January for summer harvest. Peas, lettuce, and spinach can go directly in the ground by late January, taking advantage of your median February 28 last frost date. These crops actually prefer cool soil and air temperatures.

March represents transition season when cool-season crops reach maturity while warm-season preparation begins. Direct-seed carrots, radishes, and beets through mid-March. Start tomato and pepper seeds indoors around March 1 for transplanting after your April safe date. Cool-season crops planted in January reach harvest stage during March’s moderate temperatures.

April through May launches warm-season planting in earnest. Transplant tomatoes, peppers, and eggplant after soil temperatures stabilize above 60°F — typically mid-April. Direct-seed beans, squash, and cucumbers from mid-April through May. These crops establish rapidly as Growing Degree Day accumulation accelerates through spring.

August through September focuses on fall crop establishment. Plant broccoli, kale, and cabbage by early August for fall harvest. September planting of lettuce, spinach, and other leafy greens provides continuous harvest through winter months. This timing captures the September-October sweet spot when heat moderates but frost remains months away.

Planning for Occasional Zone 7-8 Events

Winter Storm Uri in February 2021 brought San Antonio temperatures to 6°F — far below typical Zone 9a minimums of 20-25°F. The January 2025 freeze event similarly pushed temperatures into Zone 7-8 territory, damaging plants rated for normal San Antonio conditions. These outlier events occur roughly once per decade but require resilience planning.

Select cold-hardy cultivars as insurance against extreme events. Choose citrus varieties grafted onto trifoliate orange rootstock, which survives brief exposure to 15°F. Plant backup quantities of tender perennials like rosemary and sage that can be easily replaced after severe freezes.

Maintain portable protection materials year-round — frost cloth, old sheets, and small space heaters stored for emergency deployment. These outlier freezes often arrive with little warning, making preparation essential. Established fig trees and muscadine grapes typically recover from Zone 7 events, while tropical plants like bananas and avocados may die back to roots but often regenerate.

Your Heat Management Strategy

San Antonio’s summer heat — peaking at 85.3°F average in August with 1096 Growing Degree Days — creates different challenges than winter cold. Cool-season crops like lettuce, spinach, and peas shut down once temperatures consistently exceed 80°F, typically by late May. Plan these crops for fall through spring windows, avoiding summer entirely.

Warm-season crops require heat management strategies during peak summer. Tomatoes stop setting fruit when night temperatures stay above 75°F — common in July and August. Choose heat-tolerant varieties like Heatmaster, Phoenix, and Homestead 24 that maintain production through extreme heat. Afternoon shade cloth reduces heat stress on peppers and eggplant during 100°F days.

Water management becomes critical as heat accumulates. Deep, infrequent watering encourages root development that supports plants through heat stress. Mulching reduces soil temperature fluctuations while conserving moisture. Many gardeners shift to early morning or evening garden work during peak summer, avoiding midday heat that stresses both plants and people.

Heat-loving crops like okra, Armenian cucumber, and Malabar spinach actually prefer San Antonio’s summer conditions. These alternatives provide fresh vegetables when traditional crops struggle, diversifying harvest through the challenging summer months. [INTERNAL_LINK: san-antonio-tx-growing-season]

About This Data

This frost date information comes from NOAA’s 1991-2020 climate normal dataset, representing the most current 30-year average for weather station USW00012921 in San Antonio. This station provides the official temperature record used for agricultural and horticultural planning throughout the region.

USDA Plant Hardiness Zone classifications reflect the 2023 update, which incorporated recent climate data showing warming trends across Texas. Growing Degree Day calculations use the standard base temperature of 50°F employed by agricultural extension services nationwide. Chill hour accumulations represent typical years, though individual seasons may vary significantly from the 200-450 hour range.

Fruit tree compatibility ratings combine hardiness zone data with chill hour requirements published by university extension services and commercial nurseries. Demographic data comes from U.S. Census Bureau estimates for Bexar County, Texas. All statistical projections assume continuation of current climate patterns, though individual years may deviate substantially from these averages.