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Today
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Soil 6 cm
31°C
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Gardening in San Diego
AI field guide · refreshed weeklySan Diego Gardening: Early Fall Planting & Heat-Loving Harvest
Zone 10b means frost is nearly absent—your last spring frost was months ago, and your first fall frost won't arrive for many months (if at all). Soil at 30°C (86°F) is still warm enough for heat-loving crops but cooling into the sweet spot for fall planting. You have roughly 366 frost-free days annually, so timing here is about heat tolerance and water availability rather than frost protection.
Sow outdoors now
Leafy greens (lettuce, spinach, arugula)
Direct sow now as heat begins to break; choose heat-tolerant varieties like 'Jericho' lettuce or 'Space' spinach for September germination. Expect germination in 7–10 days with consistent moisture.
Radishes (Cherry Belle, Icicle)
Sow directly into beds; mature in 25–30 days and tolerate the remaining heat well. Keep soil evenly moist to prevent cracking.
Peas (sugar snap, snow pea)
Sow now for winter/spring harvest; they'll germinate slowly in warm soil but establish roots before cooler weather arrives. Inoculate seed with rhizobium if soil is new.
Carrots (Nantes, Chantenay types)
Direct sow in loose, well-draining soil; germination is slow (14–21 days) in warm soil, so keep seed bed consistently moist. Thin seedlings to 5 cm (2 in) spacing.
Brassicas (broccoli, cabbage, cauliflower transplants)
If buying transplants, plant them now so they establish before winter; direct seeding is slower and riskier in residual heat. Space 45–60 cm (18–24 in) apart.
Start indoors now
Tomatoes (fall crop: 'Sungold', 'Black Cherry')
Start seed indoors now for transplanting in 4–5 weeks; fall tomatoes mature as temperatures drop, concentrating flavor. Use a heat mat to maintain 24–27°C (75–80°F) soil.
Peppers (long-season: 'Anaheim', 'Serrano')
Start seed indoors; peppers need 60–90 days to transplant size and will fruit through winter in San Diego's mild climate. Keep soil warm and moist.
Herbs (cilantro, parsley, dill)
Start indoors in small pots for transplanting in 3 weeks; cilantro especially bolts quickly in heat, so getting a head start indoors lets you plant out as temps drop. Succession-sow every 2 weeks.
Harvest now
Summer squash (zucchini, yellow crookneck)
Pick daily when 15–20 cm (6–8 in) long to encourage continued production; plants are still vigorous in early September heat.
Eggplant (Japanese, Italian types)
Harvest when skin is glossy and firm; cut with pruners to avoid damaging the plant. Plants will keep producing through October.
Basil
Pinch flower buds and harvest leaves regularly to extend the season; basil thrives in current heat and will decline as temperatures drop below 15°C (59°F).
Tasks this week
- Water deeply and early morning—soil at 30°C dries fast; mulch beds with 5 cm (2 in) of compost to retain moisture and cool roots.
- Scout for spider mites and whiteflies on heat-stressed plants; spray neem oil in early morning or late evening if populations spike.
- Deadhead spent flowers on ornamentals and herbs to redirect energy into new growth before fall planting intensifies.
- Prepare beds for fall crops by amending with compost; remove spent summer plants and dispose of diseased foliage.
- Check drip irrigation for leaks and clogs; September heat can stress systems, and consistent moisture is critical for germinating seeds.
Watch out for
- Powdery mildew: High humidity (40%) combined with warm days and cool nights favors fungal growth; ensure good air circulation and avoid overhead watering.
- Transplant shock: Seedlings started indoors need hardening off (7–10 days of gradual outdoor exposure) before planting in full sun.
- Soil compaction: Heavy watering and foot traffic in warm, moist soil can compact beds; work in organic matter and avoid walking on planted areas.
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