Upland, CA

Upland's growing season never stops. With a last spring frost of January 4 and a first fall frost of December 30, the frost-free period runs virtually the entire calendar year. Frost is almost never a limiting factor; gardeners here can plant warm-season crops (tomatoes, peppers, eggplant) from January onward and maintain productive plantings without interruption.

The real constraint is summer heat. Upland sits in the San Gabriel Valley foothills, where summer temperatures regularly exceed 95°F and often push past 100°F in peak July and August. Unlike coastal Southern California, the inland location means low humidity and intense direct sun. Cool-season crops like lettuce, broccoli, and peas thrive in the mild winters but face significant stress during summer months.

Mediterranean and heat-adapted crops show their worth here. Figs, pomegranates, and Asian persimmons handle the heat without complaint. Goji berries are naturally adapted to this climate. Peppers, both sweet and hot, flourish when summers are hot and water-stressed; so do eggplants. Citrus from zone-hardy varieties also performs well.

Water availability is the secondary constraint. Upland's semi-arid location means irrigation is essential, not optional. Gardeners relying on supplemental water should plan accordingly, particularly for the April-through-September stretch when rainfall is minimal and temperature peaks.

The year-round growing season is an asset. It's possible to plant continuously, to succession-plant vegetables for staggered harvest, and to maintain overlapping harvests throughout the year.

The summer heat window (June through September) defeats many home gardeners. Tender crops like lettuce, spinach, and peas cannot tolerate sustained 95°F+ temperatures and require shade cloth or complete replanting schedules. Even heat-loving tomatoes can drop flowers in extreme heat if irrigation lapses or humidity stays too low. Peppers actually thrive in this heat, but only if soil water is consistent.

Water access and cost are the second critical issue. Southern California's water restrictions mean many gardeners cannot simply run drip lines continuously through the hot months. Deficit irrigation (allowing some water stress to concentrate flavors) works well for Mediterranean crops like figs and olives, but it's a conscious strategy, not a default fallback.

Pest and disease pressure never truly drops here. Codling moth in apples, mites on pomegranates, and thrips on peppers can breed year-round without the hard frost kill-off that other zones enjoy. This requires either preventive spray programs or careful variety selection for pest-tolerant cultivars.

Shade cloth protects summer tender crops. Starting April, heat-sensitive crops benefit from 30% shade cloth (or heavier shade for lettuce and leafy greens). This extends the harvest window for cool-season crops and prevents heat stress on transplants. Remove shade cloth in November when direct sun is gentle and day length drops.

Plant in two windows, not one. Upland doesn't have a single spring planting and summer dormancy. The optimal tomato planting window is February through March (harvest by June before peak heat) and again in August (harvest through winter). Peppers go in from February through April. Winter crops (lettuce, broccoli) are planted in September and October. Map out succession timing to overlap harvests year-round.

Amend soil for drainage. High desert soils in this region are often alkaline and compact. Work 3 to 4 inches of compost into planting beds annually to improve drainage, add organic matter, and buffer pH. This is especially critical for figs and pomegranates, which need good drainage to avoid root issues in irrigated settings.