What to Plant in Santa Cruz & the Bay Area in September

Seasonal Planting
Written By Adrienne Gaughan

September in Santa Cruz County is still full-on summer in many areas. While days are getting shorter, temperatures are often at their hottest - regularly hitting the 90s and even 100s in inland valleys and sunny mountain areas. Coastal areas stay cooler but are still warm.

This is NOT yet fall weather, but it IS an important planting month. You're planting cool-season crops that will grow slowly in September heat, then take off when temperatures finally cool in October and November.

Why September Temperatures Matter

Don't let the calendar fool you - September is often our hottest month, especially inland:

  • Sunny mountain areas (Boulder Creek ridges, Ben Lomond chaparral, Scotts Valley hills): Regular 90-100°F days, low humidity

  • Under redwoods (Felton canyons, shaded Ben Lomond areas): 10-15°F cooler, more moisture

  • Inland valleys (Scotts Valley, Soquel): High 80s to mid-90s

  • Coastal (Aptos, Capitola, Santa Cruz): 70s-80s, more stable temps

  • Watsonville/Pajaro Valley: Mid-80s to low 90s

You're still harvesting summer crops heavily, and tomatoes are absolutely still producing. In warm microclimates, they'll continue through October and even into November.

Direct Seed These in September

Cool-Season Crops (will germinate slowly in heat)

  • Lettuce (shade it, choose heat-tolerant varieties early month)

  • Arugula

  • Spinach (late September better than early)

  • Mustard greens

  • Chard

  • Mizuna

  • Asian greens (bok choy, tatsoi - late September)

  • Mâche (wait until late September)

Root Vegetables

  • Radishes (quick varieties)

  • Turnips

  • Beets

  • Carrots (all month)

Legumes

  • Peas (late September in cooler areas)

  • Fava beans (late September)

Herbs

  • Cilantro (finally won't bolt immediately!)

  • Dill

  • Parsley

Cover Crops

  • Fava beans

  • Clover

  • Vetch

Transplant These in September

Brassicas (if you started in July/August):

  • Broccoli

  • Cauliflower

  • Cabbage

  • Kale

  • Collards

Other Transplants:

  • Lettuce (give afternoon shade)

  • Onions (from sets for spring harvest)

  • Strawberries (excellent month!)

What to Harvest in September

Peak summer harvest - September is NOT winding down yet:

  • Tomatoes (still going strong!)

  • Peppers (peak production)

  • Eggplant

  • Summer squash and zucchini

  • Beans

  • Cucumbers

  • Melons (late varieties)

  • Early fall greens (if you planted in July/August)

  • Apples and pears

September Garden Tasks

  • Continue harvesting summer crops heavily

  • Direct seed fall greens and root vegetables

  • Transplant brassicas started earlier

  • Plant strawberries

  • Succession plant beans and summer squash if you're in a warm microclimate

  • Water deeply - September is still dry and hot

  • Shade new plantings of cool-season crops from afternoon sun

  • Start planning fall garden but don't pull summer crops that are still producing

  • Save seeds from heirloom tomatoes and peppers

Microclimate-Specific Advice

Coastal (Aptos, Capitola, Santa Cruz beaches, Live Oak): You have the most stable temperatures - warm but not extreme. September is excellent for planting cool-season crops. Your tomatoes are still producing but may slow down earlier than inland areas. Plant everything on the list. Fog has largely cleared but afternoons are pleasant.

San Lorenzo Valley & Scotts Valley - Sunny Ridges/Chaparral (Boulder Creek mountains, Ben Lomond sunny exposures, Scotts Valley hills, sandstone areas): You're experiencing 90-100°F days regularly. Summer crops are thriving - don't pull them! Your tomatoes will produce through October and possibly into November. Plant cool-season crops, but give them afternoon shade and consistent water. They'll grow slowly now but take off in October. You have huge temperature swings from day to night.

San Lorenzo Valley & Scotts Valley - Under Redwoods (Felton canyons, Ben Lomond shaded areas, Scotts Valley valleys): You're 10-15°F cooler than the sunny ridges nearby - maybe high 70s to mid-80s. Better conditions for cool-season crops. You may have more moisture retention. This is a great time to plant greens and brassicas. Less temperature swing than sunny areas.

Inland Valleys (Soquel hills, inland Santa Cruz): High 80s to low 90s. Similar to sunny mountain areas - still hot! Summer crops are producing well. Plant cool-season crops with shade and good watering.

Watsonville/Pajaro Valley: Mid-80s to low 90s, warm and sunny. Your agricultural climate means excellent conditions for both late summer crops AND fall plantings. You have the longest season - take advantage of it.

Common September Questions

Is it too late to plant tomatoes? No! In warm microclimates (sunny mountain areas, Watsonville), tomatoes planted in early September can still produce in November. But you need fast-maturing varieties and transplants, not seeds.

Should I pull my tomato plants? Absolutely not, unless they're diseased or you desperately need the space. September tomatoes are at their peak in most areas. In warm microclimates, they'll keep going through October and even into November. Let them produce!

Why aren't my lettuce seeds germinating? It's too hot! September soil temperatures are still in the 70s-80s, which is above ideal germination temps for lettuce. Try pre-sprouting seeds indoors, planting in shade, or waiting until late September. Coastal gardeners have better luck than inland.

Is it too late to plant brassicas? Early September? You're fine with transplants. Late September? You can still plant kale and collards, but broccoli and cauliflower might not have enough warm days to head up before winter.

When should I plant garlic? October is traditional, but late September works in warmer areas. Wait for the heat to break slightly.

The September Reality Check

Most gardening advice says "September is fall." Not here! September is:

  • Still summer temperatures

  • Peak harvest for summer crops

  • Planting time for fall crops (that will grow slowly until October/November)

  • Continued need for irrigation and pest management

  • NOT the time to pull productive plants

Heat Management for September Plantings

Since you're planting cool-season crops in summer heat:

  • Shade new plantings from afternoon sun

  • Water consistently - soil is still drying out quickly

  • Choose heat-tolerant varieties of lettuce and greens for early September

  • Wait until late September for most cold-hardy crops

  • Pre-sprout seeds indoors before planting

  • Mulch heavily to keep soil cooler

Make September Count

September is a transition month, but the transition is slow. You're simultaneously:

  • Harvesting summer crops at their peak

  • Planting fall crops that will grow slowly now, rapidly later

  • Still dealing with summer heat and dry conditions

  • Preparing for the eventual arrival of fall weather (November)

Don't rush to pull summer plants. Don't expect fall weather. Work with the heat you have.

Adrienne Gaughan
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