Houston, TX

Houston's gardening calendar is defined not by winter cold but by summer heat and humidity. With a last spring frost of February 13 and a first fall frost in early December, the growing season extends nearly 10 months, one of the longest in the continental United States. Winter temperatures rarely drop below 25°F, making the zone's lower bound a minor constraint for most crops.

The real boundary here is heat. Summer temperatures regularly exceed 90°F, often climbing above 95°F from June through September. This heat advantage means tropical and subtropical crops thrive where they barely survive elsewhere in zone 9b: figs produce heavily, jujubes flourish, pomegranates set abundant fruit, and Asian persimmons color without winter dormancy stress. Goji berries adapt well to the climate.

But heat also eliminates or complicates crops that need cold dormancy or cool-season growth. Traditional cool-season vegetables (lettuce, peas, broccoli) must be planted in fall and harvested before summer heat arrives, then replanted in late summer and fall again. Summer tomatoes and peppers are standard fare, but the opposite problem arises: many traditional varieties bolt, sunscald, or stop setting fruit in July heat. Houston gardening is really two seasons: a long, mild winter and spring (February through May), and a long, hot summer and fall (June through December), with a brief cooldown in January.

Humidity is the persistent enemy. Year-round warmth and high moisture from the Gulf create ideal conditions for powdery mildew, downy mildew, and fungal leaf spots that would be winter-killed farther north. Pruning for air circulation and avoiding overhead watering help but rarely eliminate the pressure.

A second hazard is the late February warm spell followed by frost. Seeds and transplants go in after February 13 (statistically frost-free), but a March freeze can devastate tender new growth. This pattern recurs most years. Starting too early in February is a common mistake.

Third, summer heat stress stops many crops mid-season. Cool-season crops planted in spring bolt and die by late May. Tomato and pepper flowers drop in sustained 95°F or higher heat. Shallow soils dry out in weeks. Gardeners often abandon summer vegetable growing altogether, an unnecessary surrender given the fall abundance.

Plant cool-season crops (brassicas, lettuce, peas) twice a year: fall (September through October for winter harvest) and late summer (late July and August) for spring. Use 30 to 50% shade cloth in May through September if growing tomatoes, peppers, or leafy greens in summer; full sun works in winter and spring.

Take advantage of the March through May window for warm-season crops. Transplant tomatoes and peppers in late February (shortly after the last frost date of February 13), and they'll establish strong root systems before heat arrives. A mid-May mulch refresh and drip irrigation setup pays dividends in June heat.

Monitor the December first-frost date (around December 9) for late-season frost-sensitive crops like tropical figs or recently planted tender perennials. A frost cloth or water spray application can extend the frost-free date by several weeks if a sudden cold snap threatens.